low and high speed damping

[The Pookster]

Originally Posted by 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.

Sorry, you've completely lost me.

[Apricot Slice]

Originally Posted by 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.

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]

Originally Posted by Apricot Slice

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=kZyEL...eature=related

[mrspeedy]

This is another neat slo-mo video - http://www.youtube.com/watch?v=KubZ2...eature=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]

Originally Posted by baw888

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]

Originally Posted by 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.

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]

Originally Posted by 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.

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.

[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

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

[SlowOne]

Originally Posted by Alfonzo

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

Keep it up guys

Glad to see someone else has worked it out!!

[Apricot Slice]

Came across these. thought they were quite interesting animations.
http://physics-animations.com/Physic...h/sprs_tmp.htm
http://physics-animations.com/Physic...h/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.