low and high speed damping

[Apricot Slice]

Hi all,
Does anyone have an interest in hi and low speed damping?
And got any ideas why manufactures have not come up with anything yet?
Apricot Slice

[mole2k]

Our shocks at the moment have adjustable high and low speed damping... ?

[Apricot Slice]

Our shocks at the moment have adjustable high and low speed damping... ?

err.. is that a question or a statement?

[crashingbird]

Hi all,
Does anyone have an interest in hi and low speed damping?
And got any ideas why manufactures have not come up with anything yet?
Apricot Slice

I think it's been done yet, RPM used to make "2stage dampers", and at the moment there's the popular high end brand GHEA, who makes the 'tapered pistons' for several 1/10 en 1/8 kits, for the same purpose (low in, high out)

http://www.rpmrcproducts.com/faq/pistons.htm

http://www.ghea.se/index.php

http://www.oople.com/forums/showthread.php?t=29087&page=5

[mole2k]

It's a statement, the question mark was in case I had picked up the wrong end of the stick and you had meant a difference in the car speed or something like that.

Any r/c shock out there reacts differently in high speed and low speed damping due to the laminar and turbulent flow of the oil.

[Apricot Slice]

I have seen the rpm pistons. you can use them as they state in the instructions to give more damping on the bound stroke and less on the rebound. this will help out on landings from big jumps. It will not improve handling though.
Fitted up side down it would act like typical low speed damping on a full sized car shock.



""It's a statement, the question mark was in case I had picked up the wrong end of the stick and you had meant a difference in the car speed or something like that.
Any r/c shock out there reacts differently in high speed and low speed damping due to the laminar and turbulent flow of the oil. ""

Yes, of course. the flow of oil passing through an aperture at different speeds has different reactions.
Take for example a B4 shock, or even a Tamiya Hotshot shock absorber which has a valve in it.. its all low speed damping.
Please take a look at the link to understand better the term high and low speed damping.
http://www.blackartdesigns.com/id4.html

[James]

A few have tried staged springs also, thats never really seemed to catch on though.. yet

[The Pookster]

Nothing about at the moment that I know of that allows you to tune high and low speed damping independently.

There are pistons about that allow you to adjust bump and rebound independently, such as Ghea and RPM.

I'm just starting to work on this for the RC world starting with proper damper dyno characterisation of all the current different damper pistons out there, will take a while to get results.

[Si Coe]

I assume you are refering to something like the platform damped shocks used on mountain bikes - which actually originated on real offroaders. These use variable pressure valves on the pistons to make the shock massively stiff (due to being over damped) to slow compression forces (such as those in cornering or accelerating) , but can be very soft and smooth for fast impacts (such as a bump).
Perfected it would allow you to set the car really soft for riding over bumps, without fear of it pitching and rolling into corners.

Basically the technology is simple enough that it could be fitted into an RC sized shock, but it wouldn't be possible to fit external adjustments (as on mtb shocks) and it would have to be a sealed unit (no oil changes) so ulitimately its not as good as we have now.

[Apricot Slice]

I assume you are refering to something like the platform damped shocks used on mountain bikes - which actually originated on real offroaders. These use variable pressure valves on the pistons to make the shock massively stiff (due to being over damped) to slow compression forces (such as those in cornering or accelerating) , but can be very soft and smooth for fast impacts (such as a bump).
Perfected it would allow you to set the car really soft for riding over bumps, without fear of it pitching and rolling into corners.

Basically the technology is simple enough that it could be fitted into an RC sized shock, but it wouldn't be possible to fit external adjustments (as on mtb shocks) and it would have to be a sealed unit (no oil changes) so ulitimately its not as good as we have now.
What I'm talking about is shock absorbers that work as they should.
Shock absorbers that allow the wheel to ride over the bumps and dips and maintain ride height and keep the tire in contact with the ground. Shocks that will bound rapidly without pack or over resistance to cope with the big bumps at speed without launching the car skyward.
So yes. like mountain bike shocks, racing car shocks etc.

If some sealed shocks appeared, as if by magic, on your car, (shocks that perform as their larger brothers do) it would be highly likely that they would out perform the competition in all situations anyway and negate adjustment.

External adjustment and sealed units pressurized with gas would not be manufacturable and be extremely complex. not to mention wildly expensive.

But however, there is a way of doing it cost effectively and maintaining the ease of use.

[Apricot Slice]

Nothing about at the moment that I know of that allows you to tune high and low speed damping independently.

There are pistons about that allow you to adjust bump and rebound independently, such as Ghea and RPM.

I'm just starting to work on this for the RC world starting with proper damper dyno characterisation of all the current different damper pistons out there, will take a while to get results.
This sounds very interesting. Are you testing just competition shocks. Any particular scale?
What kind of equipment do you use to test them?

[The Pookster]

This sounds very interesting. Are you testing just competition shocks. Any particular scale?
What kind of equipment do you use to test them?

I'm going to be testing an AE shock with bleed cap with a variety of pistons, AE, 1,2,3, LOSI, Ghea etc and oils to measure what the real differences are rather than any conjecture.

Will be done on a full size Roehrig damper test machine such as this:

http://www.roehrigengineering.com/Products/4K-EMA-magnetic-linear-actuator-research.htm

[Chrislong]

How about something like the British Leyland Hydro-spastic? With a single oil reservoir, it'd be nuts, crap, oh and nuts.

It is possible to create a shock absorber from magnetic fields rather than oils, and the possibility is endless. But for me some of the enjoyment comes from the tuning of things like shocks, to remove this would remove it as a tuning factor, and remove any reward for making the car handle extremely well.

[Apricot Slice]

I'm going to be testing an AE shock with bleed cap with a variety of pistons, AE, 1,2,3, LOSI, Ghea etc and oils to measure what the real differences are rather than any conjecture.

Will be done on a full size Roehrig damper test machine such as this:

http://www.roehrigengineering.com/Products/4K-EMA-magnetic-linear-actuator-research.htm

I will be interested to see the results. especially the comparisons with with the larger bore shocks.

Will you be testing for durability also?

[Apricot Slice]

How about something like the British Leyland Hydro-spastic? With a single oil reservoir, it'd be nuts, crap, oh and nuts.

It is possible to create a shock absorber from magnetic fields rather than oils, and the possibility is endless. But for me some of the enjoyment comes from the tuning of things like shocks, to remove this would remove it as a tuning factor, and remove any reward for making the car handle extremely well.
Personally I like innovations and new stuff that makes things better and faster.

[Legacy555]

You could take existing real car technology.
Put a solid piston in, have a valve (or 2 stage/twin valve set) at each end of the shock, adjust them to activate at different pressures. Run a tube from top valve(s) to bottom valve to create oil loop. This means you could have fast and slow bump and rebound. Not rocket science.

Probably more advancements to be made with the delevopment of a diff unit that could do away with the slipper assembly rather than such over engineered suspension. Micro Hydradrive that replaces idler gear????

[Apricot Slice]

You could take existing real car technology.
Put a solid piston in, have a valve (or 2 stage/twin valve set) at each end of the shock, adjust them to activate at different pressures. Run a tube from top valve(s) to bottom valve to create oil loop. This means you could have fast and slow bump and rebound. Not rocket science.

Probably more advancements to be made with the delevopment of a diff unit that could do away with the slipper assembly rather than such over engineered suspension. Micro Hydradrive that replaces idler gear????

I would like to see a diagram of that.

doesn't have to be over engineered. I think it could be done with less than half a dozen easily manufactured parts.

er.. what is a micro hydredrive?

[Legacy555]

I would like to see a diagram of that.

doesn't have to be over engineered. I think it could be done with less than half a dozen easily manufactured parts.

er.. what is a micro hydredrive?

is a viscous coupling. Actually that would have to be on the layshaft gear rather than the idler.

[MRD]

The easiest way to make a piston with different bump and rebound is to have a piston with 4 holes in it with a reed valve on the top covering two of the holes. Going up the valve would be forced shut so only two holes are open, going down the valve opens and all four holes are open.

Its as simple as a disk of rubber clamped to the top of the piston using the c clip with only half of the holes in it that the piston has.

Easy peasy. :lol:

[Apricot Slice]

Are there any racers out there that would interested in more advanced shock absorbers?
(assuming of course that they would give you an advantage over the competition)

[InsideLineModels]

The easiest way to make a piston with different bump and rebound is to have a piston with 4 holes in it with a reed valve on the top covering two of the holes. Going up the valve would be forced shut so only two holes are open, going down the valve opens and all four holes are open.

Its as simple as a disk of rubber clamped to the top of the piston using the c clip with only half of the holes in it that the piston has.

Easy peasy. :lol:

This is something that has been available on the Predator Shock absorbers for quite some years. I have to be honest, i've not played with it too much though.

I think the main use was in the front to slow the shocks on rebound to help stop the nose lifting on acceleration.

Kev

[The Pookster]

This is something that has been available on the Predator Shock absorbers for quite some years. I have to be honest, i've not played with it too much though.

I think the main use was in the front to slow the shocks on rebound to help stop the nose lifting on acceleration.

Kev

That was the original intention (I remember trying these with Richard Weatherley when he was developing the Pred in his back garden...), and to copy how road car dampers are set-up where there is more rebound to control the spring recoil force.

[JohnM]

Are there any racers out there that would interested in more advanced shock absorbers?
(assuming of course that they would give you an advantage over the competition)

Whats the point? If it could be done, and If they worked that well, everyone would buy them, and then there wouldn't be an advantage;)

At least now, you can try/hope to get an advantage by setting your car up better then someone else.

[JohnM]

This is something that has been available on the Predator Shock absorbers for quite some years. I have to be honest, i've not played with it too much though.

I think the main use was in the front to slow the shocks on rebound to help stop the nose lifting on acceleration.

Kev

I'm sure that was something you could do on Supershot shocks back in 1986ish.

[Apricot Slice]

Whats the point? If it could be done, and If they worked that well, everyone would buy them, and then there wouldn't be an advantage;)

At least now, you can try/hope to get an advantage by setting your car up better then someone else.


Whats the point.. you said it :- "If it could be done, and If they worked that well, everyone would buy them";)
Also it would be nice to be responsible for some technical advancement in a sport that i really dig.

[Chrislong]

Im with JohnM on this, well and truly.

Things like diffs - im for reducing maintenance/increasing reliability, going with gears etc (still tuneable though!). But for shocks, they should ALWAYS be tuneable.

If something was made, which was sealed, untuneable, worked everywhere and gave a massive advantage over what we have now (I don't see how btw, without re-writting rules of physics, cars handle great when setup well) - yes, we'd all have to use them to not be at a dissadvantage - but I personally would dislike that, and im sure many others would also dislike it. Id hope for the BRCA to not allow them - which id propose and attend AGM to vote on.

[Apricot Slice]

Im with JohnM on this, well and truly.

Things like diffs - im for reducing maintenance/increasing reliability, going with gears etc (still tuneable though!). But for shocks, they should ALWAYS be tuneable.

If something was made, which was sealed, untuneable, worked everywhere and gave a massive advantage over what we have now (I don't see how btw, without re-writting rules of physics, cars handle great when setup well) - yes, we'd all have to use them to not be at a dissadvantage - but I personally would dislike that, and im sure many others would also dislike it. Id hope for the BRCA to not allow them - which id propose and attend AGM to vote on.



I think you kinda got the wrong end of the stick there mate. Maybe i didn't make the point clearly.

I'm pretty sure though that if you had a shock absorber that behaved exactly like the full sized ones do only scaled down, then it would out perform any shock with a simple piston with some holes drilled in it. (even one that is well dialed in)
okay, so you may have to re write the laws of physics or something to prove it. but hay, it a hypothesis. Lets not take things out of context.

Actually I would vote the same way. If some magic shock arrived on the seen that were very very expensive it would make the high end of the sport inaccessible. which is not.. well, sporting.

As i said earlier, I think a better solution is possible with less than half a dozen easily manufactured parts and be inexpensive.
The design is quite simple and would allow me to adjust the shocks in the same way as usual and have some additional options.
The only big difference would be using bump stops to cushion landings instead of using pack.

[MRD]

I think the general idea of adjustable rebound shocks has been lost in this thread. Somewhere along the line these magic sealed ultimate shocks have been drempt up that will walk all over standard shocks, this is pure fantasy. Even with adjustable bump and rebound the oils and pack would need to be changed depending on the track, all it would do is improve the current setup, so if you cant set up shocks for toffee then they wont help.

As far as cheating, whats to say what is and isn't? Big bores seem to be the big thing at the mo and at £80 they are pricey and out of reach of some racers so do we ban these too?

If they could make these magic dampers then they would come with the top end kits so its a bit of a mute point really :lol:

[Apricot Slice]

okay MRD, so you think the idea of improving something floored is ridiculous and that i am a cheat.:thumbdown:



If there is anyone interested in the development of shocks that work better than what is currently available or have something constructive to say, please let me know.

[James]

Are you going to make some?

Would this hi/lo business affect how a car generates mechanical grip through its roll centres? You need the body to roll in order to do this so how would a system treat the forces this would be applying? fast or slow? And if if there is a transit point between hi/lo where the shock stiffens/softens would this affect how the roll centre works?

The only way to know is to try it, ask any R/C company in the world - its great on paper but things can be totally different when tested on the track.

I'm all for innovation though.. :thumbsup:

[MRD]

okay MRD, so you think the idea of improving something floored is ridiculous and that i am a cheat.:thumbdown:



If there is anyone interested in the development of shocks that work better than what is currently available or have something constructive to say, please let me know.

:lol: Wrong end of the stick mate, I'm saying its NOT cheating. Please re-read my post ;)

I am sayin that people worried that there will be an all conquering shock have nothing to worry about as it isn't going to happen, what will happen is that there will be improvements to standard shocks that will make them better but will still need setting up properly.

I used the big bores as an example of improvements that are happening right now which are expensive but still aceptable, in reponse to people that say expensive tuning options are cheating and shouldn't be allowed.

I'm all for improvements in the hobby.

Like I said, re-read my post.

[Apricot Slice]

Are you going to make some?

Would this hi/lo business affect how a car generates mechanical grip through its roll centres? You need the body to roll in order to do this so how would a system treat the forces this would be applying? fast or slow? And if if there is a transit point between hi/lo where the shock stiffens/softens would this affect how the roll centre works?

The only way to know is to try it, ask any R/C company in the world - its great on paper but things can be totally different when tested on the track.

I'm all for innovation though.. :thumbsup:


I have some designs that i think will be effective. whether i actually go balls out and commit myself to making parts and a test rig depends on if i can manage it on my own.

you have got some good questions there... blimey! where do i start.

first of all, slow speed.(slow speed damping is what we have on the standard shocks) that is the main part of the damping that is responsible for the pitch and roll effects on the chassis.
too soft and it gets wollowy and too firm and it gets bouncy and you lose the weight transference and traction etc. so somewhere in the middle keeps the tire where its supposed to be and maintains feel and response.
(typically 'pack' is incorporated into the shocks as its a very effective way of surviving landing impacts but has detrimental effects to the handling at speed when traversing bumps for obvious reasons.)

the slow speed damping would incorporate heavier damping on the rebound stroke. something like 60/40. (many full size cars have twice the damping on the rebound) its a starting point.
this 60/40 ratio is designed to maintain spring compression so that the 'average' ride height is maintained even wile the suspension is waggling up and down over ripples n stuff.

high speed damping. basically this is the opposite of pack.
imagine you are going at speed and you hit a bump. the wheel shoots upward at great speed as it goes over the bump, this fast movement makes the shock 'pack' and too much energy, too quickly, is transferred to the chassis.
this situation will unsettle the chassis and raise the average height and over continued bumpiness will have the buggys wheels off the ground.
high speed damping relieves the shock of this massive load by backing off with the damping effect and allows the length of the suspension to comply with the offending bump and maintain chassis equilibrium.

bump stops would have to be used in the absence of pack to survive heavy landings.

the aim is to improve ride height stability and to keep the tyres in contact with the ground. and if the shocks allow this, then the handling results should reflect your setup.

of course, the theories have to be tested. I would make a test rig to do this. i couldn't rely on my driving skills as they are not too good. i would have to find someone good to do track testing for me.

[Matt Airbrushing]

Thanks for such an informative post Apricot :)

So this could be acheived on an RC car with some sort of pressure relief valve for high speed damping? Either on the piston or as a bypass from one "side" of the shock to the other.

Very interesting thread :D

If you could make this work then it wont result in uber dampers that work everywhere but would make damper tuning much more complex.

[James]

high speed damping. basically this is the opposite of pack.
imagine you are going at speed and you hit a bump. the wheel shoots upward at great speed as it goes over the bump, this fast movement makes the shock 'pack' and too much energy, too quickly, is transferred to the chassis.
this situation will unsettle the chassis and raise the average height and over continued bumpiness will have the buggys wheels off the ground.
high speed damping relieves the shock of this massive load by backing off with the damping effect and allows the length of the suspension to comply with the offending bump and maintain chassis equilibrium.

I like this ^^

bump stops would have to be used in the absence of pack to survive heavy landings.

I very much dont like this ^^

the aim is to improve ride height stability and to keep the tyres in contact with the ground. and if the shocks allow this, then the handling results should reflect your setup.

I like this ^^


Something that strikes me is the reference to full size cars, but you dont often see full size vehicles jumping 10 times their own height regularly on a race, the useable stroke on a full size car will be very little methinks compared to an R/C car, i would imagine the forces are exponential too ? Will the hi/lo work on such an extreme action?

[Matt Airbrushing]

I dont see why not.

It depends on how clever the shock design is.

The bump stops dont have to be solid, you could use secondary springs that are only used at the extremes of suspension travel, although this would negate some of the advantage of the high speed damping.

At the moment you are having to ballance damping between jumps, bumps and roll, so its all a compromise.
If you could set low and high speed damping you will still have to compromise, but you will have more options... and the possibility of a better setup.

[MRD]

The nearest thing I can see to 1/10 off road in the full size world is proper short course trucks, they seem to handle very large drops with an element of stability in the bends so maybe this scaled down would work?

[Matt Airbrushing]

The nearest thing I can see to 1/10 in the full size world is proper short course trucks, they seem to handle very large drops with an element of stability in the bends.

Paris - Dakar rally trucks also face big drops and need good high speed handling.

Im not sure if these vehicles have anything unusual in terms of suspension setup, I wonder if we can find any technical information.

[SlowOne]

Fascinating thread. Couple of things to throw in the research...

First, it isn't the height the car gains that counts, it's the energy that you are trying to dissipate. Despite the height, the videos I've recently seen of Off-Road cars seems to show that, despite the height, the landing is quite soft, as you guys try to catch the downslopes of jumps and land the car like an aircraft. In those situations the spring/damper isn't doing a great deal of work.

Second, the main reason that this has never happened before is because whilst we can scale the size of the cars, we can't scale the Laws of Physics. All the ideas from full-size shocks rely on oils working in large spaces with large strokes, whereas we work in small spaces with short strokes. The basic characteristics of the oil remain, so, for example, the reaction time is slower relative to the movements of the suspension for our cars than a road car.

I tried the idea MRD wrote about with small flaps on piston holes back in the day. It did alter the compression/rebound ratio, but despite all sorts of testing, we never could get it to react fast enough, and eventually we abandoned it. I remain sure that the first person/company to crack a variable rate damper will sell their product like hot cakes, as it will improve handling and roadholding.

However, there will be no silver bullet, nor product monopoly - if there were only one killer way of doing it, there would only be one damper for all road cars, race cars and bikes. Since changing damper suppliers is a regular feature of race teams and road car manufacturers, it's clear that there is a lot remaining to be developed in damper world. There is constant change in the damper market, so once this is started, it will be the same in off-road RC. You might want a better damper, but be careful what you wish for!! :)

[Apricot Slice]

bump stops would have to be used in the absence of pack to survive heavy landings.

I very much dont like this ^^



Something that strikes me is the reference to full size cars, but you dont often see full size vehicles jumping 10 times their own height regularly on a race, the useable stroke on a full size car will be very little methinks compared to an R/C car, i would imagine the forces are exponential too ? Will the hi/lo work on such an extreme action?


Bump stops V's pack
because pack is effective for the most part of the piston stroke its effectiveness is hard to beat for a smack down landing.
It is something i have thought quite a lot about and have come up with various ideas like broaching the side walls inside the shock body to give variable damping but am not sure about the manufacturability of this.

your mention of not seeing full size cars doing massive jumps is a good point.
at tenth scale though, impacts from massive jumps are not nearly as destructive.

you can see quite a meaty bump stop nugget towards the end of this vid
these things take quite a bashing.
http://www.youtube.com/watch?v=3N-YOLjZg-8

Some folks mention the difficulty of setting up more complex shocks.
sure, it would make things more complex.
but its child's play compared to most normal motor sport.

personally i like all the technical challenges in r/c racing and would hate to see something dummed dowm because it might be difficult to understand.

[The Pookster]

Without question RC dampers could be much more advanced in terms of how the damping forces are achieved and in what direction. I also think it would not be too difficult to make some real gains on the track as it would improve the handling/large jump/bumpy track compromise.

But this needs to be developed carefully using real data as a guide and using real road/race car damper experience. Not wishing to upset anyone but it is plainly obvious on this thread that no-one has this understanding. I feel in a position to say this as I'm currently employed as a steering/handling technical specialist for a major car company.

Lastly, gains that could be made with the dampers would be at the expense of complexity, i.e. the number of options and interactions of damper internals would be so complex most racers would struggle to get a good balance. Sometimes keeping it simple means you get slightly less performance but for more of the time.

[MHeadling]

It seems there are already these adjustable shocks out there, I know the 5th scale lads run similar shocks to these but they are about £400 a set for the 5th scales:

http://www.neobuggy.net/modules/news/article.php?storyid=6654

http://www.expertmodel.com/

[MHeadling]

English link to website:

http://www.expertmodel.com/eng.html

[Apricot Slice]

It seems there are already these adjustable shocks out there, I know the 5th scale lads run similar shocks to these but they are about £400 a set for the 5th scales:

http://www.neobuggy.net/modules/news/article.php?storyid=6654

http://www.expertmodel.com/

These are some pretty cool looking shocks.
look like a solid piston. with all of the oil passing the needle valve.

[Apricot Slice]

Without question RC dampers could be much more advanced in terms of how the damping forces are achieved and in what direction. I also think it would not be too difficult to make some real gains on the track as it would improve the handling/large jump/bumpy track compromise.

But this needs to be developed carefully using real data as a guide and using real road/race car damper experience. Not wishing to upset anyone but it is plainly obvious on this thread that no-one has this understanding. I feel in a position to say this as I'm currently employed as a steering/handling technical specialist for a major car company.

Lastly, gains that could be made with the dampers would be at the expense of complexity, i.e. the number of options and interactions of damper internals would be so complex most racers would struggle to get a good balance. Sometimes keeping it simple means you get slightly less performance but for more of the time.


I think there is a sensible compromise between complexity and better results. (not forgetting that everyone is using piston damping in its most basic form) and that this avenue is ripe for development.

Of course my designs may be doomed to failure because of a lack of understanding and bad design, etc.
If my designs are good and my understanding is on track, no pun intended, as you say, careful development would have to take place of which I have little experience.
Were i to do it on my own, a hands on, trial end error type testing is the only way forward as maths and science isn't what I'm good at.

Ultimately I'd like to be able to make a manufacturer/team an offer they would find hard to refuse and see them get big results.

[gps3300]

bump stops would have to be used in the absence of pack to survive heavy landings.

I very much dont like this ^^


Technically speaking, modern full size cars don't have bump stops anymore but "spring aids". On older vehicles a bump stop was simply a lump of rubber placed to stop a metal to metal clash at full jounce. Modern suspension designs tend to use a carefully tuned tapered cone of elastomer which engages much earlier than a bump stop and as I understand it works a bit like the concept of a dual-rate spring as the suspension arm loads up.

This idea can easily be recreated on a 1/10th buggy, however I'm not sure if a full size car uses them for handling or ride comfort (or perhaps both?).

[Apricot Slice]

Technically speaking, modern full size cars don't have bump stops anymore but "spring aids". On older vehicles a bump stop was simply a lump of rubber placed to stop a metal to metal clash at full jounce. Modern suspension designs tend to use a carefully tuned tapered cone of elastomer which engages much earlier than a bump stop and as I understand it works a bit like the concept of a dual-rate spring as the suspension arm loads up.

This idea can easily be recreated on a 1/10th buggy, however I'm not sure if a full size car uses them for handling or ride comfort (or perhaps both?).

I like this red one http://www.off-roadweb.com/tech/0904or_bump_stop_tech/photo_11.html
Its a very agreeable colour yes?

[Matt Airbrushing]

Does anybody know if gas shocks have ever been tried on an RC car?

I did some designs for oil shocks but they will be very complicated (similar to the design shown in the link above)

A gas shock might be simpler to manufacture, but im not sure if they would work very well (if at all)

[The Pookster]

Technically speaking, modern full size cars don't have bump stops anymore but "spring aids". On older vehicles a bump stop was simply a lump of rubber placed to stop a metal to metal clash at full jounce. Modern suspension designs tend to use a carefully tuned tapered cone of elastomer which engages much earlier than a bump stop and as I understand it works a bit like the concept of a dual-rate spring as the suspension arm loads up.

This idea can easily be recreated on a 1/10th buggy, however I'm not sure if a full size car uses them for handling or ride comfort (or perhaps both?).

Spring aids is the correct modern term and they create a compound spring rate curve in combination with the spring. They are better than having a progressive spring as you have more options in terms of their characteristic and where they contact in the travel.

They perform multiple functions for handling in terms of balance and smoothness of breakaway as well as ride control on large bumps and providing the end stop for the suspension on potholes and such like. Quite time consuming and complicated to develop.

For an RC application the material simply can't be made soft enough to act as a spring aid but if it could then they would be quite advantageous.

[The Pookster]

Does anybody know if gas shocks have ever been tried on an RC car?

I did some designs for oil shocks but they will be very complicated (similar to the design shown in the link above)

A gas shock might be simpler to manufacture, but im not sure if they would work very well (if at all)

Not sure what you mean?

Gas shocks have oil in them, they provide the damping as normal with a piston moving through oil. The gas part is a seperate chamber that is pressuized with gas and has a floating piston that pushes on the oil. Basically it means the damper is capable of producing higher forces without the oil cavitating as it moves though the piston at high speed.

Practically all cars sold these days have gas shocks of this type. Some cheaper aftermarket dampers use the gas dispersed through the oil.

[The Pookster]

It seems there are already these adjustable shocks out there, I know the 5th scale lads run similar shocks to these but they are about £400 a set for the 5th scales:

http://www.neobuggy.net/modules/news/article.php?storyid=6654

http://www.expertmodel.com/

This discussion thread is about shocks that are much more complicated than those on the link.

They basically have an adjustment that bleeds off oil during the stroke so you can have a finer control over the amount of damping, rather than just step change between piston hole size. But they don't offer any advantage in terms of differences between bump and rebound or low and high damper speeds.

[SlowOne]

The bump stops idea we used (back in the day!) by putting fuel tubing over the shock shaft. The tubing could be adjusted for length, and by taking 'nicks out of the sides with a scalpel, we could change the 'rate' of the bump stop to be more like the spring assist.

The 'gas' shock Pookster describes we already have, albeit only at atmospheric pressure. The bladder in the top of a lot of shocks acts like the gas piston on top of the oil, its just that we don't put any pressure behind it above atmospheric pressure.

[Apricot Slice]

If only one of the damper speeds can practically be made to have differing rates of bound and rebound. which would you say is the most important to have it on?
(I would assume that the high speed side would be far more important.)

[The Pookster]

The 'gas' shock Pookster describes we already have, albeit only at atmospheric pressure. The bladder in the top of a lot of shocks acts like the gas piston on top of the oil, its just that we don't put any pressure behind it above atmospheric pressure.

Actually this isn't quite right. The diaphram is there to prevent the damper from hydraulically locking when it is compressed. This is because as the piston rod enters the damper it takes up space, and oil is incompressible, so the diaphram and air behind it allows for this. Any change in pressure is so small is has pretty much no effect.

If you take a bleed type damper like an AE with bleed cap and lock the bleed screw before the damper is compressed fully you won't be able to push it in any further.

[The Pookster]

If only one of the damper speeds can practically be made to have differing rates of bound and rebound. which would you say is the most important to have it on?
(I would assume that the high speed side would be far more important.)

You need to think about this a bit more and understand the damper.

All dampers produce different damper forces at different damper speeds, so they are already variable. Best practical way to experience this is simply to take the damper off the car and push the rod in and out at varying speeds to feel the difference.

The events on the track happen at different damper speeds, handling is fairly low speed, bumps can be mid to high speed and landing off a big jump is high speed.

The compromise with an RC damper is there because this relationship is fixed, i.e. it produces more force as you move it faster exactly the same way no matter what oil and piston you use, it's just the overall amount that changes. If you had a more complex piston you could start to change these relationships to tune one bit for handling, one for jumps and one for ride on the bumps based on different dampers speeds on different events as above.

[ghea]

Hi Guys,

First I like to say this thread is awesome.

When we first started making pistons I was not sure how they really worked,so I figured that I had to measure them to fully understand what happens.

With some help from a friend we started to build this machine for measuring low to high speed damping forces and we can also simulate different pack situations.

When you measure for example a 16mm big bore piston from low to high speed you will find them to be quite linear up to the high speed area where the damping force gets more progressive.

With our pistons we make the damping force more linear than standard pistons and that's what make the cars calm down.

Today we are testing what we call "pack control" that means you just change oil with outside temperature to get the right low speed damping and choose the piston depending on what high speed damping you need.

Thanks/Ronny Guta
GHEA

[Apricot Slice]

Hi Ronny,
That's a great looking workshop you have.

The first thing that came to mind for a test rig was a large rolling road. and have a camera mounted so results can be examined in slow motion.
Not very scientific.

It would be very interesting to hear about your machines.

Phil

[TSewell]

I agree with Ghea, this thread is awesome.

To me, the aspect that is missing in all of this is real data. Having a shock dyno is great, and they are fairly straightforward (but not cheap) to build for RC use ....However the missing components are things like damper speeds (how often does the shock go up and down in 1 second on the track? Some 1:1 road race cars have damper speeds of 20in/s!) and how they relate to lateral accelerations.

The way to get this is with an onboard datalogger with 3 axis accelerometers and shock position measurement (probably linear potentiometers as used in full scale). With this, and a shock dyno, real repeatable results can be attained.

Sound impossible? A few years ago it might have been, but digital electronics have made huge strides in the past few years. I am attempting to do this very thing. I have the following so far:


http://www.sparkfun.com/commerce/product_info.php?products_id=8627

http://www.sparkfun.com/commerce/product_info.php?products_id=9431

I am still looking for a way to measure shock position in real time. Linear pots are expensive..anyone want to whip me up some custom hall sensors that I can run in the preload collars ?

Travis Sewell
Mechanical Engineer

[SlowOne]

Actually this isn't quite right. The diaphram is there to prevent the damper from hydraulically locking when it is compressed. This is because as the piston rod enters the damper it takes up space, and oil is incompressible, so the diaphram and air behind it allows for this. Any change in pressure is so small is has pretty much no effect.

If you take a bleed type damper like an AE with bleed cap and lock the bleed screw before the damper is compressed fully you won't be able to push it in any further.Mmmmm... So what's the difference between a piston sat on top of the oil with gas pressure behind it (as described in your earlier post), and a diaphragm sat on top of the oil with atmospheric pressure behind it? I get that the road damper has a pressure greater than atmospheric which helps, but...

Isn't the theory the same? Without the compressible gas behind the piston, the increasing volume in the oil of the advancing piston rod would cause both systems to hydraulic, wouldn't they? I think you're confusing application with theory here...

One thing's for sure; once someone does come up with a more tunable damper, that particular genie will be out of the box and may well turn into a source of regret for your class. Whenever things get more technically complex, and makes it more difficult for the average Joe or Jane to go racing, the class suffers. Off-Road is the ideal class right now, since you have that greatest of all levelers - more power than grip. As I said before, be careful what you wish for!

[Apricot Slice]

Mmmmm... So what's the difference between a piston sat on top of the oil with gas pressure behind it (as described in your earlier post), and a diaphragm sat on top of the oil with atmospheric pressure behind it? I get that the road damper has a pressure greater than atmospheric which helps, but...

Isn't the theory the same? Without the compressible gas behind the piston, the increasing volume in the oil of the advancing piston rod would cause both systems to hydraulic, wouldn't they? I think you're confusing application with theory here...

One thing's for sure; once someone does come up with a more tunable damper, that particular genie will be out of the box and may well turn into a source of regret for your class. Whenever things get more technically complex, and makes it more difficult for the average Joe or Jane to go racing, the class suffers. Off-Road is the ideal class right now, since you have that greatest of all levelers - more power than grip. As I said before, be careful what you wish for!

the main difference is that the nitrogen filled jobs of full size car shocks prevent cavitation as oils passes through the various valves and holes etc. as the Pookster said.
i suspect that if you tried the same thing on tenth scale shocks, the rods would get shoved frimley out to their fullest extent. i suspect also that forces aren't big enough on model cars to get cavitation.
other than that, i think the purpose is very similar.
But I aint no expert..

[elvo]

Off-Road is the ideal class right now, since you have that greatest of all levelers - more power than grip. As I said before, be careful what you wish for!

Or more power than thumbs :thumbsup:

I'm not wishing for scaled down adjustable 1:1 shocks. As someone posted before, the cars scale down, but the physics don't. 1:5 scale cars and planes are still close to realistic - I think wind tunnel tests are often done on scale models that are ~1:5. But anything 1:10th or smaller, forget realistic shapes or realistic handling. Water especially doesn't scale. For example: a 1/10th model of a speed boat doesn't work. A 1:10th speed boat that does work, does not look like a boat at all. Dirt doesn't scale either: realistic-looking dirt tyres don't grip, and real off-road trucks don't use spikes or pins.
Oh, and it works the other way as well: I don't think the jumps we have in off-road racing scale up :woot:

I don't think we want shim stacks to soften high-speed damping.

Needle-adjusted low speed damping and a floating piston look interesting, but sealing any kind of pressure on a 3mm shaft will be challenging...

[ollie]

Our shocks are just plain to small to even consider some of the damper technology that’s been posted within this thread.

You also have to consider an R/c cars scale speed if you transferred this up to full size then I am afraid your full size cars suspension would react the same as your R/c car.

[Apricot Slice]

Racing today was fun. perfect weather for it up here in oil country.
One of the new guys had a Schumacher Cat SX2. Schumacher sure do make cars that look good. like an engineers wet dream. I want one.
The shocks are mega silky smooth and the springs dead run true. nicely made.

Our shocks are just plain to small to even consider some of the damper technology that’s been posted within this thread.

Most likley there were ques of people lined up to tell Patek Phillippe, in the late 18th century, that his idea was utterly impossible.

You also have to consider an R/c cars scale speed if you transferred this up to full size then I am afraid your full size cars suspension would react the same as your R/c car.

I don't understand what you mean. Can you explain please?

[Col]

I think Ollie means that for all our cars are "10th"scale they only weigh approx 1/100th that of full size?

[SlowOne]

I think what he means is that if we were truly 10th or 12th scale then the full-size version would be doing something like 250 to 350mph. Imagine what the suspension of a Baja buggy doing 250mph would be doing - apart from tearing itself to pieces!!

If a 1:1 WRC car on something like the Acropolis Rally was doing 100mph across rough terrain, then our cars should be doing something like 10mph. If you drive your car at that speed, the suspension is very well behaved!! I'm guessing Off-Road cars do something like 25mph, and at least 5mph in the tightest turns. That would mean the WRC car doing 250mph on the straights, and about 50mph in a tight turn. Just imagine what that would do to the suspension!!

[Apricot Slice]

A 10th scale car doing 10mph does not equate to a full size car doing 100mph. Simply multiplying the speed by the scale does not work.

An example from the real world:-
A whippet can reach speeds of 35 mph and is very close to a half scale grey hound. Yet you do not see a grey hound running at 70mph. More like 40mph.
Similarly, the top speed of a humming bird is equal to that of a goose.

The scale speed calculation which provides the most realistic performance where the scale model performs in a realistic manner:-
The speed is found by multiplying the 'real' speed by one over the square root of the scale.

A 10th scale model doing 25mph equates to a full scale speed of about 75mph.


I think Ollie means that for all our cars are "10th"scale they only weigh approx 1/100th that of full size?

maybe 1000th even?

(thats weird.. i think my spell check messed with the 'th')

[Col]

Sorry, dude, you're going to have to provide evidence on all that above.
I've not spoken to a whippet recently, but I also don't remember a whippet ever claiming it was a 1/2 scale greyhound

[Apricot Slice]

Sorry, dude, you're going to have to provide evidence on all that above.
I've not spoken to a whippet recently, but I also don't remember a whippet ever claiming it was a 1/2 scale greyhound
Ok. I will give it my best shot. or to be more specific, I will give it Bob's best shot.
First check out Bob's creds.http://www.astroflight.com/index.php?main_page=product_info&cPath=29&products_id=166
here is a link to a PDF file that Bob wrote on scale.http://docs.google.com/viewer?url=http%3A%2F%2Fwww.astroflight.com%2Fpdfs %2FScaleSpeed.pdf
Not all of this stuff applies but none the less an interesting read.

[Gayo]

Some of you may remember the Micro-Racing Cougar, an 80's 1/8th nitro buggy with adjustable oil loop shocks.
http://www.twf8.ws/new/other/museum/cougar.jpg



Wouldnt it be (kind of) easier to scale down Bose-type suspension? Electromagnetic computer-driven suspension, that is.

<object width="480" height="385"><param name="movie" value="http://www.youtube.com/v/eSi6J-QK1lw&hl=fr_FR&fs=1&rel=0"></param><param name="allowFullScreen" value="true"></param><param name="allowscriptaccess" value="always"></param><embed src="http://www.youtube.com/v/eSi6J-QK1lw&hl=fr_FR&fs=1&rel=0" type="application/x-shockwave-flash" allowscriptaccess="always" allowfullscreen="true" width="480" height="385"></embed></object>

That's so cool BTW :woot:

[SimonW]

The way i see it is, If your 2.2 inch 1/10th wheel and tyre hit a 10mm bump at 30mph on your model car that would equate to your average 15 inch wheeled 1/1 scale car hitting a bump of about 70 mm. With a model car you would struggle to notice the bump, if you drove your family saloon up a kerb at 30mph you would at least smash your alloy wheel and worst case push the strut through the bonnet. You would need a monster truck like the Gravedigger to get a reaction similar to that of a model car and those monster trucks DO have great big disproportionately large dampers and 2 for each wheel at least. Our little toys have simple yet highly effective dampers really all things considered.

[TSewell]

Any active suspension is illegal per ROAR, EFRA, and IFMAR rules. As per the scaling factor, prove to me that it exists in fluid dynamics and win a nobel prize :thumbsup:

Honestly though, we run a power to weight ratio in excess of F1, with chassis stiffness that they could only dream of in relation to their damper rates. From an engineering perspective, it is a very interesting design problem.

I have decided to build a shock dyno. I plan to use a real time force measurement device (load cell on datalogger) and get real data. I have a full CNC machine shop at my disposal, and CAD software. This is the best comprise, aside from a 7 post shaker ( which I hope to someday build, someday:drool:).

Fluid mechanics are really, really complicated. Aside from doctorate level math, I really think the only way is trial and error on a repeatable test device.

FYI; the spring damper equation is:

Force= Spring Rate (K, in lb per inch) times spring compression (X, in inches) + Damping Coeffecient (C, in lbs per inch speed) times velocity ( in inches per second)

So

F= KX+CV

The objective of the shock dyno is to find a graph of C versus velocity . I plan to post these for most popular piston/oil combos, but if anyone else has this info, please share :)

[ghea]

thought i could share some pictures of our rigg.
we can measure 1.5hz(stroke per second)to 55hz
thats about 2meter/second
To simulate a car dropping from 0.5 to 1 meter we have the weight with
the wheel on.
I will post testresult on our homepage when i have some time over.

[elvo]

r we have the weight with
the wheel on.

Brilliant!

[elvo]

As per the scaling factor, prove to me that it exists in fluid dynamics and win a nobel prize

From http://en.wikipedia.org/wiki/Microfluidics:

"The behavior of fluids at the microscale can differ from 'macrofluidic' behavior in that factors such as surface tension, energy dissipation, and fluidic resistance start to dominate the system."

[TSewell]

From http://en.wikipedia.org/wiki/Microfluidics:

"The behavior of fluids at the microscale can differ from 'macrofluidic' behavior in that factors such as surface tension, energy dissipation, and fluidic resistance start to dominate the system."


Elvo, exactly my point. Folks were trying to relate what is going on in their shocks to some linear scaling factor, ie 1/10th, 1/2, etc. Microfluidics is really cool subject matter, and there is still a ton to be learned ie fluid behaviour.

[SlowOne]

My point exactly - you can scale the size and weight but you can't scale the Laws of Physics. All these phenomena are present in full-size cars, gas turbines, etc.

Scale is an easily defined word, it means to use numbers to measure or compare the level of something. In that sense, we can scale everything that we do in modeling and make comparisons. However, it doesn't work that well when things start to move. However, you can't say there is no comparison since, if there weren't, none of the experiments above would be worth doing!!

The last time I looked a whippet was about 20" tall and a greyhound about 28", so hardly half-scale. And, according to Science Daily, their high athletic ability is probably due to a genetic mutation. Apart from that, great analogy!! :p

[Apricot Slice]

Hi Ronny,
Thank you for posting those pictures. That's a nice setup you have there.
Looks easy enough to make but would be a whole new project deciphering results!


My point exactly - you can scale the size and weight but you can't scale the Laws of Physics. All these phenomena are present in full-size cars, gas turbines, etc.

Scale is an easily defined word, it means to use numbers to measure or compare the level of something. In that sense, we can scale everything that we do in modeling and make comparisons. However, it doesn't work that well when things start to move. However, you can't say there is no comparison since, if there weren't, none of the experiments above would be worth doing!!

The last time I looked a whippet was about 20" tall and a greyhound about 28", so hardly half-scale. And, according to Science Daily, their high athletic ability is probably due to a genetic mutation. Apart from that, great analogy!! :p

I would like to apologise to any disgruntled whippets.

[The Pookster]

What are people's understanding of the term 'pack' in regards to damping levels?

[Bomberpilot]

Hello Guys,
this thread is very intersting, so my 5 cents:
the " problem " of our shocks seems to be, that high-speed ist to strong, which unsettles the car. But we need strong damping in low speed ( 0.5-1.5 Hz ) to give a driveable feeling and controlling wheigt transfer.
Some companies like Asso or Tamiya and Losi have these shocks witout blades, there is an oil/air mixture in it, which helps to soften the highspeed because the air bubbles expand under the piston.
Shocks like that have been used in those stadium trucks ( the real ones) in the 80is. The where position sensitive too...some iteresting books about that are availible

As somebody said, chaning stacks and stuff would make our cars very hard to setup, so the way is to think about floating pistons, maybe to slow down the last few mm's in rebound and to use an air/oilmixture in the shock.

One thing, chassis roll does not induce weight transfer, otherwise a pan car would not have weight transfer...its the moments which make the weight transfer.

Sorry for my english.

Maurice

[Apricot Slice]

What are people's understanding of the term 'pack' in regards to damping levels?
I figured it may be something like this.
http://www.oople.com/forums/[IMG]http://i471.photobucket.com/albums/rr74/Zogg538/pack.jpghttp://www.oople.com/forums/[IMG]http://i471.photobucket.com/albums/rr74/Zogg538/pack.jpghttp://www.oople.com/forums/[IMG]http://i471.photobucket.com/albums/rr74/Zogg538/pack.jpghttp://www.oople.com/forums/%3Ca%20href=http://s471.photobucket.com/albums/rr74/Zogg538/?action=view&current=pack.jpg%20target=_blank%3E[IMG]http://i471.photobucket.com/albums/rr74/Zogg538/th_pack.jpghttp://www.oople.com/forums/[IMG]http://i471.photobucket.com/albums/rr74/Zogg538/pack.jpghttp://i471.photobucket.com/albums/rr74/Zogg538/pack-1.jpg

[MrWolf808]

Firstly can i see i have read through this thread a few times now and find it completely fascinating, both the mechanical and the fluid dynamics guys seem to be getting there point across.
So can i please just ask a (relatively) simple question, where are you now. are we looking at a 2 stage piston with a external reserve, or link from one to another. a different internal piston design or mix of the both. you have all been talking about dampers and of course it is a major component but i think that the "bump stop" issue was a bit lightly glossed over and is still a very important part of the whole situation as is spring rate. which does of course effect shock shaft speed, and hence low and high speed shaft speed.
Please forgive for intruding on a highly fascinating thread but racing 1/8th rallycross i find striking the right damper rate imperative. and would love to gleam all the information i can.

[mrspeedy]

Definately interesting stuff .....

I under stand the low speed damping thing, but what exactly is the difference between "pack" and high speed damping ? or is it the same thing ?

[elvo]

Bump stops are a no-no. The chassis has got to hit the ground before anything in the suspension starts to bind. More so, even, even with the chassis flat on the ground you need ~5mm of extra uptravel. It's easy to see why when looking at some of Jimmy's fabulous action shots: our cars roll hard and far, and tracks are not flat.
(The 1:1 dune buggy / sand rail / desert racer crew will disagree though: they'll consider it a sin if the chassis hits the ground before the shocks hit the rubber bump stops.)
Even similar things to bump stops, like increasing the spring and/or damper rates near full compression: doesn't really work. It's been tried a number of times, results have never been 100% satisfying. Often it's very nice on bumps and rough stuff, but there's always a downside when it comes to control, and 'centering up', like when lining up for jumps and flying through chicanes. It's similar to what happens if rebound and compression damping rates are too far apart: roll and pitch movements become asymmetrical and a bit weird.

This may be far out, but who says R/C cars need 'ideal' damping rates? R/C drivers' bums and spines are safely on the rostrum, they don't really care about jolts as long as the car stays in control.

[Apricot Slice]

Definately interesting stuff .....

I under stand the low speed damping thing, but what exactly is the difference between "pack" and high speed damping ? or is it the same thing ?


As the piston moves through the shock body the oil passes through holes in the piston. this gives a damping effect.
The effect is smooth and progressive for the most part.
When a certain speed is reached the flow characteristics of the oil passing through the holes change and a much higher rate of damping is the result.
This is called 'Pack'

High speed damping is damping specifically aimed at handling the effects of high speed suspension movement independently from low speed suspension movement.

(or at least that's my understanding of it. please correct me if i am wrong)

[baw888]

This is the thread I've been waiting for.

After working on numerous Mounain bike suspension systems and creating some great acting forks in the process. I though shim stack pistons in an RC car would be a breeze.
I did make some great looking pistons using Stainless steel shim material. placed above and below the piston. Covering some of the rebound holes and most of the compression holes.
After trial end error and months of rebuilding with various shims I came to the following conclusion:

It would stiffen the slow speed compression, so the car would behave like the oil was too stiff. Felt like the suspension was binding. Equals terrible handling on the bumps.
On jump landings if would let the oil flow, and the car would slap the ground.

It seemed like I had made a shock with the worst of both worlds.

So if we(you) are to ceate a damper of the next level. We need to establish what we need the shock to do, eg, what is the graph of piston speed/resistance of the ideal damper. If we can work this out, then we can engineer the rest.
Maybe we will come the the conclusion that the damper needs a linear resistance up to a point, then a higher resistance to help in landings, ie exactly what we already have.

I have had a different line of thought, Rock Shox in the Moutain bike world created a fork that basically disconnected the dampers from the wheel, and inbetween had a very stiff, short spring, that would smooth out the transition between compression and rebound. It was like riding on a very large balloon tire, But still retained the same levels of damping throughout the rest of the stroke.

Could we use this theory to let the wheel quickly react to bumps on the ground, and then be able to increase the overall stiffness of the shock.
In other words, stiffer suspension to stabalise the car and make it more drivable, but still allow the tyre to follow the ground and keep traction. Much like a Yokomo Bmax and Kyosho FS. (By using flex)

[The Pookster]

So based on Ghea's info that their measurements showed a progressive damper characteristic (getting stiffer, providing progressively more and more force) at high damper velocities this is essentially what 'pack' is.

When landing from a jump or on larger bumps the damper will be travelling at high velocities so pack in compression is useful. But because an RC damper is simple you'll also get 'pack' in rebound which is not desired as it unsettles the car on bumps or a rough track. I assume this rebound 'pack' is what the Ghea pistons take away.

I will be measuring AE, Ghea and Losi pistons on a full size cutting edge damper characterisation rig soon so will find out.

And to answer some other trial and error experiments that have not been successful to date, you are setting an impossible task unless you have the damper measurement data to know exactly how it's behaving.

[The Pookster]

Bump stops are a no-no. The chassis has got to hit the ground before anything in the suspension starts to bind. More so, even, even with the chassis flat on the ground you need ~5mm of extra uptravel. It's easy to see why when looking at some of Jimmy's fabulous action shots: our cars roll hard and far, and tracks are not flat.
(The 1:1 dune buggy / sand rail / desert racer crew will disagree though: they'll consider it a sin if the chassis hits the ground before the shocks hit the rubber bump stops.)
Even similar things to bump stops, like increasing the spring and/or damper rates near full compression: doesn't really work. It's been tried a number of times, results have never been 100% satisfying. Often it's very nice on bumps and rough stuff, but there's always a downside when it comes to control, and 'centering up', like when lining up for jumps and flying through chicanes. It's similar to what happens if rebound and compression damping rates are too far apart: roll and pitch movements become asymmetrical and a bit weird.

This may be far out, but who says R/C cars need 'ideal' damping rates? R/C drivers' bums and spines are safely on the rostrum, they don't really care about jolts as long as the car stays in control.

This is a somewhat negative view of the possibilities. You need to understand what bumpstops could offer and how damper performance is not about ride it is about maximising the contact load between the tyre and track for more of the time and therefore going faster. F1 invests a lot in damper technologies for the same reason and I don't think they,re interested in smoothness of ride.

[baw888]

Does anyone make a data logger for shocks this small? If we put this on the track, then we might have an idea of what speeds various bumps are producing.

[Chris Doughty]

Bump stops are a no-no. The chassis has got to hit the ground before anything in the suspension starts to bind. More so, even, even with the chassis flat on the ground you need ~5mm of extra uptravel. It's easy to see why when looking at some of Jimmy's fabulous action shots: our cars roll hard and far, and tracks are not flat.
(The 1:1 dune buggy / sand rail / desert racer crew will disagree though: they'll consider it a sin if the chassis hits the ground before the shocks hit the rubber bump stops.)
Even similar things to bump stops, like increasing the spring and/or damper rates near full compression: doesn't really work. It's been tried a number of times, results have never been 100% satisfying. Often it's very nice on bumps and rough stuff, but there's always a downside when it comes to control, and 'centering up', like when lining up for jumps and flying through chicanes. It's similar to what happens if rebound and compression damping rates are too far apart: roll and pitch movements become asymmetrical and a bit weird.

This may be far out, but who says R/C cars need 'ideal' damping rates? R/C drivers' bums and spines are safely on the rostrum, they don't really care about jolts as long as the car stays in control.

100% agree with this.

having our chassis scrape the floor on the face of the jumps is pretty much how our cars jump nicely on the big hit jumps. especially so in 8th scale, if you have one wheel hit its bump stop it will throw the car to one side.

in an ideal world without the laws of physics I'd like the following

low speed damping - slow (for body roll and cornering)
high speed damping - fast (to deal with stutter bumps)
(now here is the catch)
high speed damping - slow (to land the big jumps)

unless there is a way to differentiate between high speed 'bump' and high speed 'landing jump' then I will stick with what I've got and put up its limitations.

adding in a curve ball, can a cars suspension geometry help to overcome what we are lacking in our current shocks and a 'magic' set of shocks not work until the geometry changes to catch up with magic shock technology?

[Chris Doughty]

This is a somewhat negative view of the possibilities. You need to understand what bumpstops could offer and how damper performance is not about ride it is about maximising the contact load between the tyre and track for more of the time and therefore going faster. F1 invests a lot in damper technologies for the same reason and I don't think they,re interested in smoothness of ride.

I don't think Elvo is being negative, I'd call is realistic, I know Elvo and I know that all of his opinions come from real-world test experiences, I've also experienced similar effects to what Elvo describes.

if you have ever driven a car where the suspension travel does not allow the wheel past the chassis when the chassis is flat on the floor you will know how garbage it really is, especiallyf if it happens to be the rear wheels!

[c0sie]

the top speed of a humming bird is equal to that of a goose.

Best sentence ever! :thumbsup:

[MrWolf808]

i dont think its a case of being right or being wrong, realistically we are not trying to stop the chassis from hitting the floor, considering the speeds and flight times especially at high speeds and not taking into consideration driver error (a high factor in my driving), we have to expect the chassis to hit floor, its just a case of making the shift from big landing to control again that matters. surely the same theory applies there the slower the transition at full compression at high speed the more effective the "landing" its the speed of the piston at that point that you need to control. surely its the engagement of a second piston or secondary spring, how about a smaller spring at the very top of the stroke internally on the damper.

[baw888]

Quote
low speed damping - slow (for body roll and cornering)
high speed damping - fast (to deal with stutter bumps)
(now here is the catch)
high speed damping - slow (to land the big jumps)

We can make this happen.
What about bump stops that move, or more like a seesaw with the bump stops on each end. If the car is flat then both bump stops engage and stop the car hitting the floor. (In turn leaving the car closer to its natural state ready for th next turn or whatever)
But when cornering, ie, when one arm is raised and the other in droop, the bump stops can move to allow this to happen.

[The Pookster]

low speed damping - slow (for body roll and cornering)
high speed damping - fast (to deal with stutter bumps)
(now here is the catch)
high speed damping - slow (to land the big jumps)


Not sure what you mean?

Low speed is slow damper velocity, measured in metres per second say. Damper force is measured in Newtons.

When you say slow, fast, slow do you mean damper velocity or force?

[Chris Doughty]

I should have been clearer with my descriptions

low speed damping(body-roll) - equivilant of thick oil - slow reaction
high speed damping(stutter bumps) - equivilant of thin oil - fast reaction
high speed damping(jump landing) - equivilant of thick oil - slow reaction

[ghea]

This is a test of a r/c piston with 3 different high speed characteristics.
The one with the most linear curve seams to work best on the track and we believe we can make them even more linear soon.

I am not sure if landings cause the fastest shock speed though?
Maybe its the rough conditions on the fast parts of the track?

To use log equipment on car seams a bit complicated to me but i am sure
some of you will get it to work:)

I think it would be easier with a high speed camera and watch the cars movement in slow motion to see whats really happen and also measure shock speed.

/Ronny

[Chris Doughty]

not the best camera work, but take a look at this
http://www.facebook.com/#!/video/video.php?v=433365433783&ref=mf

FYI - my car was too soft in this clip

[mrspeedy]

As the piston moves through the shock body the oil passes through holes in the piston. this gives a damping effect.
The effect is smooth and progressive for the most part.
When a certain speed is reached the flow characteristics of the oil passing through the holes change and a much higher rate of damping is the result.
This is called 'Pack'

High speed damping is damping specifically aimed at handling the effects of high speed suspension movement independently from low speed suspension movement.

(or at least that's my understanding of it. please correct me if i am wrong)

So hole size and "pack" is a way of increasing the higher speed damping rates then ?

I like things in simple terms :)

Just out of interest can anyone tell me why Associated pistons work differently to the Losi pistons ?

[Chris Doughty]

So hole size and "pack" is a way of increasing the higher speed damping rates then ?

I like things in simple terms :)

Just out of interest can anyone tell me why Associated pistons work differently to the Losi pistons ?

using thinner oil and smaller holes does make the flow of oil more turbulant at high speeds so yes.

light oil + small holes = more pack therefore more high speed damping rate
thick oil + large holes = less pack therefore less high speed damping rate

with the right combitnation of oil and piston both could feel very similar on the bench.

AE pistons are 2 holes, each hole is bigger than the Losi 3 hole pistons. Losi pistons also have rounded edge vs the square edged AE pistons, I'm sure this also has some effect, some oil will always get around the outside of the piston so with that in mind I'd say the Losi piston is more prone to pack

[The Pookster]

Lots of opinion on this thread, everyone's entitled to those.

Very little fact or data though.

The shock speed is not too hard to calculate. Landing from a large jump, i.e full rebound to full compression, will be about the fastest shock speed the car sees. Piston has to travel the full distance, time for this is in the region to 0.05 to 0.08 seconds by my observations and timings. As a sanity check this equates to the region of 3 to 5 Hz, which seems about right (I will be taking some measurements of my B4 to work out its natural suspension frequency soon).

On a B4 the rear shock travel is 26mm, so speed based on the above timings is 0.32 to 0.52 m/s.

If you look at the Ghea data the damper is already starting to be progresive at 0.5 m/s and the difference in the damper force, from highest to lowest, is 50N down to 40N. This is a 20% drop so a significant change and you would expect a real difference (not saying whether it is better or worse) on the car, especially as the change in force at the lower velocities is much smaller.

[MrWolf808]

a very good point but one thing i dont think we are taking into account is the force applied, you would have to have a universal spring rate to be able to calculate the force applied too the damper under each load setting. i am now trying too look up the formula to calculate the above.

[The Pookster]

a very good point but one thing i dont think we are taking into account is the force applied, you would have to have a universal spring rate to be able to calculate the force applied too the damper under each load setting. i am now trying too look up the formula to calculate the above.

Sorry, you've completely lost me.

[Apricot Slice]

Lots of opinion on this thread, everyone's entitled to those.

Very little fact or data though.

The shock speed is not too hard to calculate. Landing from a large jump, i.e full rebound to full compression, will be about the fastest shock speed the car sees. Piston has to travel the full distance, time for this is in the region to 0.05 to 0.08 seconds by my observations and timings. As a sanity check this equates to the region of 3 to 5 Hz, which seems about right (I will be taking some measurements of my B4 to work out its natural suspension frequency soon).

On a B4 the rear shock travel is 26mm, so speed based on the above timings is 0.32 to 0.52 m/s.

If you look at the Ghea data the damper is already starting to be progresive at 0.5 m/s and the difference in the damper force, from highest to lowest, is 50N down to 40N. This is a 20% drop so a significant change and you would expect a real difference (not saying whether it is better or worse) on the car, especially as the change in force at the lower velocities is much smaller.
I'm not too good at the maths side of things but wouldn't the suspension move far quicker when hitting a lump at top speed?
Even landing from a high jump, the impact speed isn't that great.
Cant be much more than 10mph unless it a very high jump.

[The Pookster]

I'm not too good at the maths side of things but wouldn't the suspension move far quicker when hitting a lump at top speed?
Even landing from a high jump, the impact speed isn't that great.

Depends on damper travel for the event. I'm talking proper big ass slapping jump, full damper travel, over very quickly.

If you hit a ridge at top speed this might produce a faster damper speed as it will be a shorter damper travel but over very quickly.

[Apricot Slice]

I hope the load sensor in your machine will register these little shocks.

I have been trying to figure out how to make a shock dyno. mechanically it dead easy. sure does get pricey for software though!

[Agt26]

I saw this video of a durango being dropped from a height in slow motion. It's interesting to see how the car absorbs the landing. If you look closely you can see how some of the wheels bounce of the ground as well.

http://www.youtube.com/watch?v=kZyELY5Eazk&feature=related

[mrspeedy]

This is another neat slo-mo video - http://www.youtube.com/watch?v=KubZ2InQiVY&feature=channel

[Rebelrc]

Just a silly one ....but has any one seen this new type of i can only assume silicone putty that is extremley soft allmost to the point of self leveling when left for a minute or so and can be stretched and compressed very easily but when hit hard becomes very impact resilliant
i saw it on the tv , they played about with it like used bubble gum then wrapped a glass light bulb in it and threw it up high and let it hit the floor ...and light blub was fine , also it retained its shape when being hit with a claw hammer
Thay are experimenting with it for stab proof comfortable clothing for the military and police
i have some ...dont know why i bought it
it sounds like to me we need an oil made from this type of silicone (reactive)
Just a bit of fun;)

[Foppa]

Another slo-mo vid going around Green Hill in Stockhlm Sweden its a bumpy track so the shocks has some work to do

http://www.youtube.com/watch?v=-wnPucyZaIY

[Apricot Slice]

It would stiffen the slow speed compression, so the car would behave like the oil was too stiff. Felt like the suspension was binding. Equals terrible handling on the bumps.
On jump landings it would let the oil flow, and the car would slap the ground.

It seemed like I had made a shock with the worst of both worlds.


This sounds like digressive in the extreme. But in my view, on the right track.

[baw888]

So wht is the conclusion with what we actually are trying to acheive?
A perfectly linear damping curve?

This might be great for corner handling, but what about the big jump landings?

These need more damping than when on other parts of the track.

[baw888]

Apricot Slice - I propose a design that,

Has a shim stack type of piston.
Low speed adjusted by diffent size holes.
High adjusted by more-less shims.

Bound curve is linear in its low speed, then tapers off to a flat line for the rest of its high speed damping.

Rebound damping set independantly.
Could be set by different size holes too.

Bottom out on larger landings is controlled by bumps stops, but stops can move and still allow wheel to move up beyond the chassis line. (in cornering only)

Could look like this.

[Apricot Slice]

So wht is the conclusion with what we actually are trying to acheive?
A perfectly linear damping curve?

This might be great for corner handling, but what about the big jump landings?

These need more damping than when on other parts of the track.
Have been thinking about this and do wonder how important it is to consider jump landing at an early stage.
If say, good results were forthcoming, (and by this i mean something that not only works well but is reliable and tuning increments are useful and in the right area) then it can then be determined if arse slap landings need consideration.

Interesting design you have there.
I like the idea you had with the pivoting bump stops/spring aids. A spot of the old lateral thinking going on there.

this may be of interest to you. http://shimrestackor.com/index.htm

[Apricot Slice]

So wht is the conclusion with what we actually are trying to acheive?
A perfectly linear damping curve?

This might be great for corner handling, but what about the big jump landings?

These need more damping than when on other parts of the track.

A linear curve up to the point where low speed damping ends and high speed begins. Not sure where the knee should be exactly. I guess at about 20mm per second. After that i would be looking for something digressive on the rebound side and linear on the compression.
http://i471.photobucket.com/albums/rr74/Zogg538/curves.jpg

[Apricot Slice]

Parts are arriving. The project is now under way.

The most expensive bit was a high speed camera. (not making a shock dyno...yet) check out the Casio Exilim range. was very surprised to find one with so much bang for buck.

[Alfonzo]

Great thread. Nerdtastic :thumbsup:

High speed camara - excellent idea. Also have a good look through Jimmy's photo's, there's some excellent ones showing the incredible suspension travel used and the behaviour of the cars. I'm always impressed by the amount of travel under braking, and fast cornering, and the squat under acceleration too.

It would certainly be a mistake to make blind direct comparisons between full size car thinking and 1:10th scale. For instance, many RC cars benefit from a degree of tunable chassis flex. I see the new Schumacher Cougar has a range of top deck tuning options for instance. In the full size race car world chassis flex is not something one would normally welcome.

Unless chassis flex is a crude way of overcoming the crudeness of simple piston & oil dampers..mmm..

Keep it up guys :thumbsup:

[SlowOne]

Unless chassis flex is a crude way of overcoming the crudeness of simple piston & oil dampers..mmm..

Keep it up guys :thumbsup:;) Glad to see someone else has worked it out!! :thumbsup:

[Apricot Slice]

Came across these. thought they were quite interesting animations.
http://physics-animations.com/Physics/English/sprs_tmp.htm
http://physics-animations.com/Physics/English/sprn_tmp.htm

[smokes]

You need the damping to work in 3 stages the first stage is called

Critical damping where the car is going over small bumps and ruts usually base on the frequency of the wheel tyre combination and air pressure.
Mountain bike shock don't do this as your body is used to do this we this out when using them on formula student cars they work and then over heat cause they couldn't cope with the Critical damping rate.

Your next stage is Yaw as the car turns this is to control the roll rate of the roll centers you, you want to set the rate so that you enable roll transfer but be to stop the car from rolling over if the tranfer is to fast.

The third is high impact landing of ramps where full stroke of the the damper is used.

This can be done by 3rd damper or 3 or 4 way damper that peugeot use to use or by a fluid that behaves similar to silly putty or custard.

I think will find that the silicon oil will exhibit a strange behaviour in the testing if you do a frequency analysis and full stroke impact loading.
This could also be dependant on how the accumulator behaves this either the air gap in assoiated type shocks or the rubber bladder in tamiya type shocks.


You need to read race car vehicle dynamics by miliken and miliken to understand the maths side of it more and the tyre side as well.

[Apricot Slice]

The project has woken up after a winters hibernation.
Early in the process some miscalculations were made and a bunch of parts had to be scrapped.
New stuff has arrived and the furious building and rebuilding of shocks has taken place.
It looks good so far. Damping rates in both high and low speed damping are easily attainable at both ends (and everywhere in between) of the usable scale.

The low speed damping is set by piston choice and damping is equal in bound and rebound. (same as conventional 10th rc shock)
High speed damping can be set independently for bound and rebound. (although provisions have been made in the piston design so that bound and rebound are proportional (not equal) using the same settings when using a particular oil weight (its complicated))

If all goes as planned, I will post some test rig video where you can see the new shocks in action along side standard ones.

[Alfonzo]

Look forward to seeing that.

[Apricot Slice]

Really great slow-mo vid here.
http://www.youtube.com/watch?v=uAhfxcMXQMU

[Alfonzo]

That's good. If nothing else it gives you a great appreciation of the sort of battering these cars take!

[Apricot Slice]

94 has quite an interesting reaction to that bump.

[Apricot Slice]

http://www.rcrevolution.net/portal/modules/news/article.php?storyid=1781

Interesting design. A little bit like a shim stack.

Anyone used these? any good?