losi xxx

[greeny]

hi all, i recently brought a losi xxx-ke and i put all my electrics in it and wieghed it. either my scales are wrong or it reli does wiegh 1505 grams is this a normal wieght or is there somethings wrong. is it normal for the XXX to be over weight or do you lot usually have to put weight in it??

if this is not correct how can i get the weight out of my car to put it where i want it?

thanx jordan

[AndyM]

my X6 weighs 16 somethin, so yors is light-weight compared to my tank :wtf: :rolleyes:

[greeny]

lol supose but considering the wieght limit is 1474 or something then i thought the car should be under wieght maybe i was asuming things, but ive raced touring cars for 4 years now and just moved onto 2wd buggies!!and every touring car ive owned (schumacher mission, tc3,yokomo SD,yokomo BD and corally RDX.) have all been under weight so it lets you put the wieght where you want.

ive been looking on helger, losi etc... for the setups and most of them say like 30 grams under fornt bulkhead and soo on. so i was abit worried thatsomething is wrong as i would like to put some wieght at the front!!

thanx jordan

[greeny]

has anyone got any tips or trcks to get the weight down???

thanx jordan:D

[tyreman]

Run the car as it is, then see if YOU feel you need to add weight to it.

I pesonally have 85grams of lead spread out in my XXXcr.

Weight isn't an issue in 2wd, as your not looking for that little bit extra duration to gear up with, dare I say it's not even important in 4wd any more either, with the cells we have today.

[Andrew Simpson]

yeah as he said

i was suprised to wen i swapped from touring car to buggy, but u jus have to forget the weight, i know sum people who run their 2wd at around the 1650 mark and who are still damn quick

i know my b4 weighs in at around 1530 and thats without the 30 grams of extra weight i run and with only piddly 3300's !!!

[bigred5765]

has anyone got any tips or trcks to get the weight down???

thanx jordan:D

weight watchers??

dont bother its fine as is
are xxxcr is closer to 1700grms

[Northy]

Who was it who said: "Light is right" ???? :confused: :confused:

[greeny]

high all im now about to build my shocks has anyone got any tips or anything to help me??

also i havent got the 27.5 oil soo which oil would be better for a bumpy, and quite jumpy track??

thanx jordan

[jcb]

I would start with 25wt in the rear shocks with a red spring and 30wt in the front with a green spring and the red / pink pistons all round. There is quite a lot of info on car set up on www.helgerracing.co.uk (http://www.helgerracing.co.uk).

Losi shocks are some of the easiest to build, fill them with oil to the bottom of the thread inside the body, leave for 10 minutes or so to let the air out. Screw in the cartridge almost all the way, push the shaft fully in and then tighten. Easy as that really. Be carefull not to cross thread the cartridge and also don't over tighten as the threads on the cartridge are quite soft and the shocks will leak if you do.

[greeny]

thats the propeblem i havent got a red spring for the rear yet i will get some when i get some money LOL soo can i do away with another spring i have blue,pink and yellow for the rear and orange, green and silver for the front!!

thanx jordan

[Northy]

Who was it who said: "Light is right" ???? :confused: :confused:

No-one? :confused: :confused: :confused: :confused: :confused:

[matdodd]

Go for 30wt front & rear with green springs on the front & pink on the rear then

[greeny]

ok will do!!!!!!!!!!!!!!

thanx jordan

[matdodd]

no problem let us know how you get on

[Gayo]

Who was it who said: "Light is right" ???? :confused: :confused:

Colin Chapman ?:confused:

[Barry Williams]

Who was it who said: "Light is right" ???? :confused: :confused:

Lena Zavaroni said it!!!!!!!!!!
So did Humphrey Davy although Thomas Edison took it one step further than Davy.

Seriously though our XXXCR's are like bricks (heavier than our XX4) & have no probs at all with speed or handling, so weight doesn't appear to be too much of an issue.

[mattym0310]

to be totally honest. compared to the weight of your CR's my x6 is obese it is so heavy! :p. doesnt affect handling tho.

[Northy]

Right guys, go here:

http://users.pandora.be/elvo/

Click the link "Weight Transfer", read all three pages. Once you understand please tell me how a heavy car handles better than a light one :confused: :confused: :confused:

[Northy]

Just to clear things up, we are really talking about 'mass' here, weight is something different.

G

[bigred5765]

without over complicating thing blow a feather then try it with a brick it sticks better mass/weight in the right place,without over doing it helps.IE why tricky and Danny McGee add weight to a over weight car

[Northy]

So then Carl, is that why all the F1 teams spend millions making their cars light? They make their cars lighter than the weight limit, then add weight where they want it, but keep the car just over the limit. They don't just add weight to the car and say bollocks to the weight limit. :confused: :confused: Or am I wrong?

[paulj]

So then Carl, is that why all the F1 teams spend millions making their cars light? They make their cars lighter than the weight limit, then add weight where they want it, but keep the car just over the limit. They don't just add weight to the car and say bollocks to the weight limit. :confused: :confused: Or am I wrong?

As far as I was aware F1 teams don't have drivers standing at the side of the track to drive the car and with a minimum weight of 600kg they have a little bit more weight than a 1/10 buggy to juggle with :p

Don't forget that weight effectively increases with speed due to the downforce at least as far as the tyre is concerned.

There is more to be gained by reducing the unsprung weight on the car compared to the overall weight too, so lighter wheel/tyre combinations or wishbones/hubs should have more effect than simply replacing all the screws with Ti or alloy but if you get the thing so light it's not staying in contact with the ground over bumps then it ain't going to do well in the corners ;)

[paulj]

Oh and I bet an F1 aero package is a lot more effective at creating downforce and grip than your pred :) ;)

N.B. Honda's current effort excepted ;)

[Dunc]

I suspect the point of adding mass is to calm the behaviour of the car. Particularly nowadays with the high speeds we are able to achieve, which translates to kinetic energy, when we hit a bump some of this energy causes unwanted movement of the car as the suspension tries to compensate. Increasing the mass will help dampen any such response and therefore, as paulj touched upon, help keep the vehicle in contact with the ground, which is where you want it.

It would appear the amount of mass people typically add is insufficient to significantly upset the other handling characteristics, as outlined on the webpage Northy linked to previously. From a brief skim of the webpages in question I suspect this is because the increase in mass of the car is not a significant percentage compared to its total mass (typically 2-5%) and I doubt the CG position is radically altered either.

[bigred5765]

well said and 1700 grms works differently than 600kg on gravity

[bigred5765]

So then Carl, is that why all the F1 teams spend millions making their cars light? They make their cars lighter than the weight limit, then add weight where they want it, but keep the car just over the limit. They don't just add weight to the car and say bollocks to the weight limit. :confused: :confused: Or am I wrong?

and u still havent explained the oil thing ae vs losi

[Northy]

If people are adding mass to keep the car in contact with the ground over bumps do you think the shocks might not be set up correctly?

G

[Dunc]

well said and 1700 grms works differently than 600kg on gravity

Thank you, glad you liked it!

So then Carl, is that why all the F1 teams spend millions making their cars light? They make their cars lighter than the weight limit, then add weight where they want it, but keep the car just over the limit. They don't just add weight to the car and say bollocks to the weight limit. :confused: :confused: Or am I wrong?

Again, paulj has pretty much answered this already, but just to expand a bit:

A Formula 1 car does weigh a lot when you consider the aerodynamic downforce acting upon it. This equates to an increased contact force at the wheels and hence more grip.

It is advantageous to generate increased (vertical) force on the wheels via aerodynamic aids because it will not affect the mass of the car or the CofG (assuming your reference point is on the chassis). Therefore the desirable handling characteristics afforded by having a light vehicle with a low CofG can be maintained whilst still generating prodigious amounts of grip.

You could achieve the same level of vertical force by drastically increasing the mass of the car, but as the link you posted suggests, this would have numerous detrimental affects on the handling characteristics.

The amount of aerodynamic downforce an F1 car is able to produce far outstrips that due to its mass alone, i.e. there is little benefit in saying "bollocks to the weight limit."

[Northy]

Some quick sums......

2wd weight limit: 1474g

A 2wd car weighing 1700g is 15% over the weight limit.

I don't know of any proffesional class of racing where they would dream of running a car that is 15% over the minimum weight limit if they could do something about it. OK, F1 might not the the best example, so lets go to WRC. When Ford first released the Focus WRC car they spent a fortune making it lighter as it was far too heavy!

:D :D :D :D :D

G

[Cockerill]

OK, lets forget F1 cars for a moment.

How about WRC cars, do they add weight to make their cars go over bumps better, or do they try to get as close to the limit as possible, I wouldn't know, best person to ask would be Jim Dixon as he prepares rally cars, I have a feeling he might say no.

[Dunc]

If people are adding mass to keep the car in contact with the ground over bumps do you think the shocks might not be set up correctly?

G

A fair point, but I think the added mass is largely to help cope with hitting perturbations at speed. This is not a dominant requirement in setting up a car; stability in corners is where it counts. These two criteria are likely to be at odds with one another so you've got to try and compromise somewhere.

[Northy]

What Dunc said......

Good post Dunc. Let me just point out here I'm not trying to say I'm right and everyone else is wrong. This is a discussion and I certainly don't want it to end up as a flame war :D :D we're all friends here. :)

F1 was not a good example, which is why in the post above I have mentioned WRC cars which are more like our toys.

Next time I speak to Jim I'll ask if he's ever added weight to a WRC car to make it handle better :D :D

EDIT: Tom beat me to it!

[super__dan]

In fairness G, not many motorsport classes have the same power to weight ratio as us though do they.

Also speak to any chassis designer about a class where they deliberatly run a soft plastic chassis as flex is prefered here rather than in the suspension setup and I guarantee they will think you'r insane, trust me I've done this and he thought I was a simpleton!

I could think of a few more things that make no sense in bugy racing given time ;)

[Northy]

Don't even get me started on flexible chassis's Dan, they're only for lazy people who can't be arsed to set thier shocks up! :D :D :D :D :D

JOKE!!!! (Sort of)

G

[Dunc]

Good post Dunc. Let me just point out here I'm not trying to say I'm right and everyone else is wrong. This is a discussion and I certainly don't want it to end up as a flame war :D :D we're all friends here. :)

F1 was not a good example, which is why in the post above I have mentioned WRC cars which are more like our toys.

Next time I speak to Jim I'll ask if he's ever added weight to a WRC car to make it handle better :D :D

EDIT: Tom beat me to it!

Northy, no flame war (or offence) intended!! :D

I just enjoy a good to and fro of intellectual thoughts, but often get a little over exuberant! :rolleyes:

I think it's hard to make real comparisons, even with similar classes such as WRC, as the way our vehicles behave is quite unique.

Imagine a full-sized vehicle doing correctly scaled speeds and jumps to our buggies! The forces involved from landings and the like would be immense, I'm not even sure it could be done.

[jimmy]

weight adds stability and slows the reactions - which on our crazy-fast cars is a good thing for lesser drivers like myself :)

[elvo]

Jimmy hit the nail on the head there.

The reason some add weight here or there is the same reason a dog licks himself: BECAUSE WE CAN :-)


Not to be disrespectful, but power-wise, WRC are pussies. As Northy might put it: we've got power coming out of our ears. And F1 is more about aero stuff than anything else. So no fair comparisons there.

I think it's just a case of the gains out-weighing (hehe) the losses: a few grammes at the front or back can be enough to bring balance to the force - or a race car, with liçttle ill effect. I've won races with a 2WD car that was 200 grammes overweight. It's not 'quick', not nimble, but 100% controllable and consistent.

And besides, making comparisons is even more difficult, I think, because we rely on a totally different sort of grip than most 1:1 racing classes. We have itty bitty little pins biting into the ground, not knobs or grooves or slicks or anything that looks remotely like a 1:1 tyre.

[xx4-nutter]

I raced my Losi xxx BK2 last night at a local club on a tight track using 4wd fronts with no weight on the front end running an 11x2 and it was awsome, i was into corners so tight and spot on, in the final keeping an X10 behind me until the last lap which i was happy about lol

last time out i was alot slower with it whilst racing with 2wd fronts, comapred to last time what a difference.. also does any one have a good starting point set up for grass for the xxx BK2 ?

Garry D.

[_sleigh_]

If it's the standard BK2 with no mods done to it, then try this.

Front

Losi 27.5wt / Red Piston / Green Spring
Shock - Middle on tower / Middle on Wishbone
Camber link - Middle on bulkhead / Outer on Hub

Rear

Losi 27.5wt / Red Piston / Red Spring
Shock - 3 on Tower / Inner on Wishbone
Camber Link - Middle on tower / Outer on Hub

Wheelbase - Medium

Anti-Squat - 1 shim under front

Ride height - set back at driveshaft level and then the front should be set so the chassis is straight (front to back)

25g in front bulkhead



If you are thinking of modding the car, then certainly look at cutting the brace between the cells and the servo out. Then dremel the area to allow the cells to move right upto the servo. That really helps gain on-power steering.

Another mod that would be worth looking at is swapping the steering to the XXX-CR rack. Again this helps smooth and equal out the steering through the corner.

[xx4-nutter]

thanks phil ill have a go with that :) and see how it goes. ive just had a good close look at my dads xxx-cr hybrid that was paul rotherhams and it has the modified parts on it lol aswell as this brace between the servo and cells done ( which ive never noticed before lol )

so whos going to the regional sunday at duhram ? i hear there is only 60 booked in??!! :confused:

Garry D.

[greeny]

just added 30 grams to the front end of my XXX hoping it will cure the onpower LACK of steering problem!!!! and i correct should this work??

thanx jordan

[tonymon]

going back to the weight thing, one thing u have to remember with our toys (lol) is that we are dealing with scale cars with the same gravitational effects as a normal car and huge power to weight ratio (already mentioned i know).

[Lee]

Very true, its the same with speed, speed is a constant regardless of the scale of the car.

Also the first thing our 2wd cars want to do is flip them selves over due to the power, and the weight distribution, possibly dan or chris could tell us if the X6 is any better?

I have added 25g just in front of my CR and its not to ride the bumps better, its to stop the front wheels lifting when i came of the banking at bury whilst trying to get the power down.

I agree with northy that the shocks should do the work and a lighter car is ultimatley faster, but on the other hand the immense power we have to hand, combined with the layout of the cars, sometimes a little weight is needed.

[paulj]

I can think of one class of racing where some controlled chassis flex is deemed a good thing...

MotoGP :)

look at the problems Yamaha ran into at the start of the '06 season with chassis setup. They stiffened the chassis(frame) from '05 and picked up loads of chatter problems making the bike very difficult even for Rossi to get the best out of it. They then couldn't run the latest 16.5, at least I think it was that size, front Michelins as this gave them more grip and increased the chatter problems.
The answer? They went back to the '05 chassis with modified pickups to suit the '06 running gear and Rossi got very close to pulling the rabbit out of the hat, oh for 0.005 seconds at Valencia...

No full scale race or rally team are going to add weight to the chassis unless they can build it below the minimum weight for the catagory and then play with ballast to fine tune the setup. But I've yet to come across a full scale catagory that has 1700g weight limit including onboard driver ;)

Northy you are comparing apples with oranges :)

[shinytopman]

weight adds stability and slows the reactions - which on our crazy-fast cars is a good thing for lesser drivers like myself :)


Good point and if you put that into context of scale speed then F1 or even WRC teams may well be adding weight !

[SHY]

This is a very complicated issue, and setting up race cars is an endless process of compromising. I will get back with a more in-depth answer. But for now, I just wanna say:

-I think Northy is absolutely right. Any race car in any class will normally be faster when it's as close to the min. weight limit as possible.

Now, one thing that significally separates R/C racing from 1:1 racing is that we in many (not all) classes have power AND run-time in excess. As long as legal we can for instance add monster wings without effecting top speed (no drag penalty).

When push comes to shove it's very much about tyre load. This is our only contact with the ground. More grip = faster.

OK. So what we basically want to achieve is as much tyre load as possible, without having to much mass to carry. That would generate too high G-forces in corners especially. Plus chassis roll. We can achieve this (F1 is extreme in that respect) by generating downforce (and/or ground effect). Since our toy cars are small, full-scale aerodynamical principles don't apply. It's for us simply a matter of:
-shoving air up (and therein generating downforce)
-how the car cuts through the air (jumping and cornering)

In order for a R/C wing to do any good, it must be both steep and large. A tiny, flat aerofoil wing will do no good but look good...

Basically then we would want a bigass wing both front & rear, as long as it is legal. (I'd really like to see in a wind tunnell test how much turbulence the rear wing would suffer from the front one btw)

Now, putting too much downforce on the chassis can also be negative, as it loads the suspension. Have you guys seen how we do it for 1:8 TR? The rear of the shell is resting directly on the rear hubs! Brilliant! Tons of downforce straight onto the rear wheels, without compressing the suspension. I'd like to see that on a buggy as well!

NB! I'm not saying here that adding more weight to the car can't be faster. I'm sure it's true, depending on the track, grip etc. Especially since we have both power and runtime to be able to carry more weight around. But what I want to point out is that it's not the best way to do it. If car A has the same amount of tyre load from high downforce and weighs 1400 grams. And car B has the same tyre load from chassis weights (and minimal wings) and weighs 1600 grams. Then car A should easily both out-accelerate, have higher cornering speed, and be less likely to roll over.

But... there's a limit (rules) to how big wings we can use. So once that's maximum, there may still be more to gain by adding weight. But that's in this class - because grip is often low. For track racing with high levels of grip extra weight is without question slower. Except when you're driving in rain (low grip).

[I'll be back with more...]

[Chris Doughty]

another thing to note....

making the 'chassis' heavier is actually making the weight percentage of un-sprung mass 'less'

sprung 750g - unsprung 750g (50/50 sprung/unsprung)
sprung 1000g - unspring 750g (can't work it out, but sprung mass is higher percentage)

rubbish figures and example I know but I don't have time for details...

whats your htoughts?

[Dunc]

another thing to note....

making the 'chassis' heavier is actually making the weight percentage of un-sprung mass 'less'

sprung 750g - unsprung 750g (50/50 sprung/unsprung)
sprung 1000g - unspring 750g (can't work it out, but sprung mass is higher percentage)

rubbish figures and example I know but I don't have time for details...

whats your htoughts?

That's an interesting point Chris, certainly not something I'd thought of. So by increasing the sprung mass of the vehicle you cause a reduction in the apparent (or relative) unsprung mass. Whether this actually reduces the impact of the unsprung mass I'm not sure....:confused:

Btw, the ratio for your second example is 57/43 ;)

[paulj]

bikes ain't that good an example either as centrifugal force has a lot of effect on handling and direction change. Yamaha run their motor in the reverse direction to Honda and pretty much everybody else in MotoGP to counteract some of the centrifugal force genrated by the wheels. This improve direction change at the cost of top end power as they need to use extra gears to get everything turning the correct way at the gearbox end. One of the reasons the Yamaha can hold a tighter line through a series of corners and and get up the inside of oponents into a corner.

I'm not sure if this would have much effect with RC cars due to the lower forces involved but it should be different in belt as compared to shaft drive 4wd?

F1 engineers would happily pay the penalty of extra weight if it could consistantly produce faster lap times :)
I'd be suprised if the old Brabham 'fan car' was below the weight limit of the time but as it almost literally 'blew' everybody away on the track with it's lap times I don't think the engineers cared about the excess weight too much. Mind you the FIA quickly found an excuse to ban it however dubious the reasons.

Chris it sounds sense to me, but that don't mean much ;) A lower unsprung weight should make the suspension work better but you still have to find the ideal settings to go with a lower weight. We don't have the benefit of suspension dyno's and real time suspension data logging or much in the way of sophisticated damping either...

[SHY]

@Chris: My initial thought is that for OR it's not significant enough. Even for 1:8 TR, which I know well from 12 years of racing and lots of testing, it's not really noticeable on the laptimes. Also lightening the drive-line (rotating mass) is theoretically supposed to give better laptimes, but again: not measurable. What is defo measurable is lightenting the car 100-200 grams (in total)... very noticeable when driving, and very noticeable on the laptimes! Racing is very much about cornering speed - that's where you win or loose IMHO.

@paulj: you mention motoGP and the centrifugal force of the wheels. Wouldn't that produce more grip? (=good stuff). You also mention 'fan cars'. IMHO here you can't put weight into consideration as this was so effective that it outweighted the possible extra weight of the fan & motor. Those (like the Chapparal) were 'vacuum cleaners' on 4 wheels, which actually sucked themselves to the ground = higher cornerings speeds and G-force recordings than ever before. The stupid thing with this solution was that they picked up all the debris on the track and blew it in the face of the drivers coming from behind.

I'd like to add another thought (before I forget). As we have this tremendous speed & power, and these really tiny tires which is our only link to the ground - I think that this is the uttermost important room for improvement in laptimes. I think that these could very well be more sophisticated: tubing, wowen in steel/etc, tyre pressure, balanced rims etc. The tires/wheels we are now using are really 'toy solutions' as I see it (unbalanced both horisontally and vertically). But then again - it might not be significant enough, so only one way to find out... Balancing them with lead etc will take away the worst vibrations and help some, but there is still more to gain I believe.

[Chris Doughty]

imagine a rippled 20 meter stretch of track.

both cars with 'nice' suspension setups on them for the cars weight

1 'barge' that weighs a lot

1 'feather' that is very light

which one would you imagine to be more 'stable' going through this section?

with regard to 'ripples' I mean small bumps that could be absorbed by suspension movement

heavy cars slowing down corner speed I completely agree with, but in off-road its not all about corners

[Dunc]

Refer to post above

First off: back with more?! There's plenty to mull over here already :D

I agree with you that a conventional wing, i.e. aerofoil, scaled down to our off-road vehicles would be next to useless due to the lack of size and speed to generate any meaningful downforce.

I don't quite agree with the mechanism you suggest for generating downforce, i.e. "shoving air up". My personal opinion is that our wings simply act as obstructions to the flow, i.e. drag devices. They cause separation of the air flow behind them (like flow around a cylinder) and therefore a pressure drag. Because the wings are mounted relatively high up, this drag generates a torque on the chassis which ultimately manifests as increased force on the rear wheels. The air being pushed up is just a result of their shape; it's not the main mechanism. The larger the steep sections at the rear of a wing, the more pressure drag you will generate and hence "downforce". I think the large sides of the wings also aids lateral stability, i.e. helps to combat snaking, particularly at low speeds when accelerating out of corners. The drag mechanism I've described will be less important under such conditions as it requires a certain amount of velocity to have any meaningful effect. This is all just guess work on my part by the way!

Very interesting point about loading the suspension, although I'm not sure how practical it would be to mount to the hubs instead on our buggies. Nor whether it's particularly detrimental, as we're not that reliant on aerodynamic effects. Intriguing all the same.....

It's true that increased weight is preferable via aerodynamic effects rather than increased mass, but because our wings are actually very inefficient, adding mass is the only practical way around it. Just my opinion.

I enjoyed reading your comments SHY, you made some interesting and valid points. I look forward to the next instalment :)

[Dunc]

imagine a rippled 20 meter stretch of track.

both cars with 'nice' suspension setups on them for the cars weight

1 'barge' that weighs a lot

1 'feather' that is very light

which one would you imagine to be more 'stable' going through this section?

with regard to 'ripples' I mean small bumps that could be absorbed by suspension movement

heavy cars slowing down corner speed I completely agree with, but in off-road its not all about corners

That's exactly what I was trying to imply in some of my previous posts. I just wasn't able to think of such a nice analogy! :)

[bigred5765]

but in essence were talking about racing in 3d offroad not 2d onroad, were jumps and bumps have a effect on the motion of the vehicle as well,and i think the whole idea of adding the weight was just to help produce front end grip and add steering, which i think can be done in the most buy other methods,
even though we run 20grms upfront in the xxxcr, and a wing

[strobe]

What are the minimum weights for 2wd and 4wd cars to race at regional and national events.

[paulj]

One thought springs to mind here which way does the motor spin in a 2wd? I've not got one to hand here, but depending on the direction of rotation it would want to either lift the front wheels or push them into the ground I'm sure this must have been thought about in 2wd transmission design? Mind you there are forces from the gears and diff spinning in the box and the pinion/spur too any ideas?

[Col]

Paul, good point. When a 2WD car is in the air (mid-jump) and you accalerate, the front wheels lift. When thought about in context to some of the previous posts, this seems to reduce the weight on the front on the car therefore reducing steering abitily. However, I suppose this also has a major benefit in that weight on the rear wheels is increased (therefore grip?) when accelerating.

[SHY]

Much obliged Dunc! ;) You talk about the 'side dams' on the wing: As I see it they mainly for OR do one thing: support & strengthen the 'main wing'. For a closed shell track car they do a lot for stability, we play around with this. But over and behind the wheels of an open wheel car there's a real mess... massive turbulence (look at the 'barge boards' on F1 cars to 'shield' the rest of aero stuff on the car). Unless we can have some molded carbon wings we have to use lexan with side stiffeners. I'm not saying it does nothing, but I bet we could not feel the difference from a stiff enough wing without side dams. (Just guessing! Rules also regulate this. If they were A LOT larger though). For track we used to be allowed to stiffen up the sides of the shell (not anymore). My findings were that flex was actually better as I could feel when the car was close to the limit. With a super stiff shell it 'just went'...

As I said, I will get back with more in-depth. I'm not an engineer, so I had to read up a lot to understand. My very good & very intelligent (sadly for him not very good looking :) ) friend Elvo and I had a very interesting discussion thread on myTSN some years ago. Luckily I kept it, so I'll make a pdf outta it and post it on the net. Before discussing aerodynamics (or more correctly: fluid dynamics) there's a lot of basics to learn first.

Still, theory can be interesting enough, but it's more fruitful to do simple on-track tests with the stopwatch. I only care about how it feels to drive and what laptimes it makes.

First of all let me tell you that track is not that different from OR. It's not 2D vs. 3D, forget that. The supspension on track cars is just as imporant, and the oil is just as black after a few runs, I can guarantee that! The asphalt tracks are far from 2D! And after doing my first 1:10 OR race I must say that the driving style is also not that different - the basic idea is the same IMHO.

Now - turbulence may very well be a more correct explanation of how our wings work, but that's not that important to know in detail. I'm used to using a lot the "Gurney" which does the same, and is very effective. What matters is that a wider, taller, and steeper wing creates more tyre load (a front wing gives more load on the front tyres).

@Chris: 'the float'... This is where I'm on shaky ground, I admit. Still I believe this is a matter of suspension settings combined with not total weight but rather the distribution of it. If they have the same shocks/springs the heavy one might float better and don't bounce around. But if the lighter car had softer shocks/springs it should handle it just as well (keep the wheels on the ground). And be faster on other parts of the track. The actual load on each tire still will be higher of course for the heavier one, which creates more traction. It will on the other hand have to push forward more mass and hence spin more. All in all it will depend on the track so it just has to be tested in each case I believe. Let's make a test and plot it in a diagram!!!

It seems to me that the cars have for a long time been a bit 'frozen' as to placement of battery cells and the motor. But now Chazz and others are finally working on that... Mr. Sideburn's ELCO seems very efficient as well! As I see it, if you go for a mid-motor 2WD and maybe at one track find it has to little rear traction - why not place 1-2 cells behind the rear axle? It's not rocket science to do that...

Mind you guys: you don't wanna end up with a fragile swiss cheese here, so we gotta find (for the believers in low weight) a way to reduce weight without reducing durability. I did my first ever 1:10 OR race last weekend and I went from 6 to 5 cells in both 2WD and 4WD. Better to drive & faster for me. Shorter runtime though, but no problem. I'm gonna try with 4 cells in 2WD as well... I'm furthermore thinking about spreading the cells more also, who says they must be one happy family always? (when I used 5 I had a foam spacer between 2 and 3, worked great). Compared to 1:1 cars our mass is kinda 'lumped together'. As to suspension setting in 2WD I used the softest AE springs and Losi #20 oil. I'd preferred even softer as it got very bumpy. I have a feeling that what's available is dialled in for 6 cells and overweight cars. When the weather is cold the viscosity is also in effect quite higher ('temperature stable' my AE).

Oh! And let me give Northy some credit for also pointing out that it's not necessarily about lowering weight per se. It can be a process of 1) lowering the total 2) putting it where more ideal. Balance is crucial for any race car. This is my goal, the problem is more how to reduce weight - these things are way too heavy and still quite slender. And to finish first, first you have to finish... So for me it's for now a question of testing all kinds of wings front & rear and playing around with 4-5-6 cells and placement.

[Dunc]

SHY, keep it coming!

I am qualified in fluid/aerodynamics, so this aspect does interest me quite a lot. I'm more out of my depth on the dynamics, i.e. suspension and geometry, side of things, so keen to learn more. With off-road it's clearly the latter that is most important in setting up a well-balanced car.

As I suggested before if the air flow separates behind an object, causing increased pressure drag, the flow will be turbulent by nature. I'm pretty sure boundary layer effects (be it laminar or turbulent) are relatively inconsequential with our buggies.

I think an important point to remember with on-road racing, particularly 1/8 IC where they run Le Mans LMP style shells, is that the whole body acts as an aerodynamic device. This combined with increased speeds brings aerodynamic affects more to the fore regarding setup.

[Dunc]

One thought springs to mind here which way does the motor spin in a 2wd? I've not got one to hand here, but depending on the direction of rotation it would want to either lift the front wheels or push them into the ground I'm sure this must have been thought about in 2wd transmission design? Mind you there are forces from the gears and diff spinning in the box and the pinion/spur too any ideas?

Correct, the motor on a 2wd spins such that the reaction torque pushes the rear of the buggy downwards (because it is mounted behind the rear axle). A classic example of Newton's 3rd law of motion. If looking at the left-hand side of a car, the motor would be rotating clockwise and so the reaction force would be anti-clockwise.

Another good example of this is helicopters. The tail rotor counteracts the reaction torque generated by the main rotor.

[Northy]

This is getting good, I'm enjoying it :) This is exactly how I wanted this thread to end up ;) ;)

G

[elvo]

. When the weather is cold the viscosity is also in effect quite higher ('temperature stable' my AE).
.


SHY buddy, these people don't understand 'AE'. :rolleyes:

[bigred5765]

Much obliged Dunc! ;)


First of all let me tell you that track is not that different from OR. It's not 2D vs. 3D, forget that. The suspension on track cars is just as important, and the oil is just as black after a few runs, I can guarantee that! The asphalt tracks are far from 2D! And after doing my first 1:10 OR race I must say that the driving style is also not that different - the basic idea is the same IMHO.

.

the suspension onroad may be as important .but when did you have to set it up to take a 20 foot impact from a landing, and i don't mean because you forgot to turn at the end of the track lol,

i made and manufactured gliders for a long time, and drag can both be good and bad, so can laminar flow, the difference between are wings we use, and one on full sized cars that work in the main is, we have no wing shape IE we use a upside down wing to produce down force, but it uses what we would call under camber. its of a singular thick thickness in a traditional wing curve shape,this produces poor laminar flow, if it was more a real wing shape IE a aeroplane wing it would produce better laminar flow and greater down force, as the air on the longer side of the wing has to travel further it also has to move faster producing a greater vacuum and down force, at less cost to drag and speed,

[bigred5765]

Correct, the motor on a 2wd spins such that the reaction torque pushes the rear of the buggy down wards (because it is mounted behind the rear axle). A classic example of Newton's 3rd law of motion. If looking at the left-hand side of a car, the motor would be rotating clockwise and so the reaction force would be anti-clockwise.

Another good example of this is helicopters. The tail rotor counteracts the reaction torque generated by the main rotor.

also its more the tyres that have a affect rather than the motor remove the wheels and try it in your hand it hardly moves then try it with wheels and tyres

[greeny]

hi all, im thinking of doing some work on my losi xxx. i was thinking about the mid motor change. is it alot of work? does it make the car any better? and do i need any knew bits to do it?

also ive been reading up on some of the convertions and is it advisable to solder the negative to he positive on a modified motor in order to get it going foward? and how would i get on about seting the timing to the euivilant that it is now with the negative and positive the other way round?

thanx jordan

[paulj]

Correct, the motor on a 2wd spins such that the reaction torque pushes the rear of the buggy downwards (because it is mounted behind the rear axle). A classic example of Newton's 3rd law of motion. If looking at the left-hand side of a car, the motor would be rotating clockwise and so the reaction force would be anti-clockwise.

Another good example of this is helicopters. The tail rotor counteracts the reaction torque generated by the main rotor.

So if the motor ran in reverse and the rotation at the diff was the same by use of gears in theory it would give more front end grip but loose you traction at the rear? How about the mid motor cars do they have the motor runing the same direction as a conventional 2wd? If not does this explain some of the differences in handling?

[paulj]

also its more the tyres that have a affect rather than the motor remove the wheels and try it in your hand it hardly moves then try it with wheels and tyres

Is this due to the weight of the wheels or their position on the car? They also have a larger diameter and I would think that this may help exagerate the gyro effect? Could be complete b@ll@cks too ;)

A good way to feel the gyro effects of spinning wheels and tyres is with a bike wheel, try holding a wheel flat in your hands and then flip it over, try it again with the wheel spinning and it will take a lot more effort to move it. This is one reason why a bike at speed is more stable than at slower speeds but conversely it takes more effort to change direction for the same reason.

[paulj]

On the subject of a light or heavy chassis how about a section of the track that has elevation changes and turns combined?
As you hit the top of the crest the momentum wants to keep the car rising so it goes 'light' over the crest, now combine this with a corner and your tyres are going to have less force pushing them down so have less grip and are not going to generate as much cornering force. A lighter chassis will be easier to lift off the ground compared to a heavier chassis at the same speed and will take longer to settle back down as it doesn't have the weight (this maybe better called mass by now I don't really know ;)) to bring it back down into full contact and full grip with terra firma.

[SHY]

Yes guys, now we're on the ball here! :)

@Elvo: if they pronounce the first three letters in the full name they will know what I mean... LOL! Dude, you tested some seasons ago a 'sectioned' rear wing (like Subaru first thought of I think) - was the difference noticeable?

As to the theoretical aspect, Elvo has thoroughly explained this aleady. Just give me a weeks time and I will post our long & interesting discussion. I find the topic fascinating as to full scale racing, it's very much a science that's not settled yet, just look to F1. We just gotta face that for model car racing we can't copy full scale solutions. It's a bit sad in a way, but true. The upside down wing shape for instance does not work in this scale as the air molecules are too big for our "insect wings" at this speed. But again, you'll get it all on a silver platter (in the meantime read Elvos articles). I can tell you straight away that insect wings as opposed to bird wings are totally flat, aerofoil wings and Bernoullis theorem don't scale down. A fly's wings just shove air around. I must say that that Predator car looks kinda cool, but I believe those wings are seriously undersized and too flat. Put on some big, steep wings! (If those shocks are progressive, that can be a good thing as that provides more traction. But it's probably like with Serpents Veteq at times difficult to figure out)

@bigred: yes, in full scale aerofoil wings are ideal. Since you mention gliders I can mention that I'm addicted to windsurfing as well. The sails we use are flat but curved (we adjust how much). Not ideal in theory compared to an aerofoil wing, but we want to surf both ways :D It works like hell! Still - let's stick to R/C - and aerofoil shapes are really 'fiddling around', we must take more extreme measures!

If you make a 1:8 scale F1 car (those bodies were used in the past, and Serpent has just made a dedicated F1 car now) it's absolutely rubbish, hardly no downforce at all. You need a big 'shovel' to deflect air (same pressure as you feel when you put your head out the window when driving) to get grip. As Dunc pointed out you can also just make turbulence. But a 'shoebox' for instance would not be very nimble when cornering etc. So it's also a matter of how the object moves through the air. The old Lolas were boxy and too nervous, the latest ones have even more grip and steering, and are also much more stable. This is due to a rounder shape and also a 'dome' in the middle. This I see is coming now also on the rear OR wings :) I wonder when we will see the first OR body with a serious dome in the shell itself. JC is already on that track with the Illuzion shell. Since the Pred has no shock towers in the way, why don't they... Not sure how much the EFRA rules would allow, but when looking at the TR501X shell there should be some room for playing about...

Now, of course aerodynamics is more important in 1:8 TR than in 1:10 OR. On the other hand keep in mind that the competition in R/C racing now is very very tuff, it's the minor details that decide which of the two experienced drivers get the upper hand. A 1:8 car really scoops up a lot of air and has probably tons of turbulece behind it (but no noticeable drag penalty as there's power in excess). The underside of the body probably also works as one large diffuser. This said, you can choose between different bodies and adjust the amount of trimstrip (Gurney). So just like in 1:10 OR there are choices to be made. To make a point: You can't win if you take off your rear wing... And... look at the X5's rear wing compared to the XX4's original wing. I'd ruffly estimate it to twice the effective size. And as I understand most guys leave the rear wings now with the 'rear wall' intact as opposed to before.

Something that's kinda surprising (to me at least) is that the wings and shells (for track) also do a lot at low speeds. Just try and take it off... remember that R/C cars are insanely fast relative to the size! When watching an onboard camera you see this very clearly!

Now - let's focus on 1:10 OR - what can we test? (I'm not thinking only XXX-CR)

Here's some ideas:
-5 cells, did anyone else try?
-4 cells (follow up with lower wind motors), anyone tried? Only for 2WD I think.
-put back weight in other areas, test 'when' it's slower
-LARGE & steep front wing, max out the rules - did anyone ever try it?
-LARGE & steep rear wing (combined with front), max out the rules - did anyone ever try it?
-move the cells around, use wires in stead of bars for testing
-make a wing mount directly on the rear hubs (only 4WD), look at the 1:8 TR solution. Accompanied with a monster wing.
-move the wing mount more to the front? (piano wire)
-where can I find springs & shock oil that is softer/thinner than what Losi and AE sells (that fits AE and Losi shocks)?

@Chris: I'm sure Atomic Carbon could do some interesting testing together with you? It takes skills & tools to make some of the solutions, especially the hub mounted rear wing. Only if you/them find it worthwhile of course. I'd really love to see a thin, molded carbon wing btw ;) I once got hold of a molded carbon gurney, it was extremely durable!

Let me stress my point though: I believe the way to go is to make you car as light as it can be as to the EFRA min. weight (is it possible???). Then generate as much downforce as possible front & rear as can be done without violenting the same EFRA rules. Then work on setup and weight distribution. THEN as our last operation we can start adding weight here and there to see if it's any help or not. Anyone agree???

[bigred5765]

5 cells we run on very loose slipper conditions, loads running it in the states. we run it at tiverton before now, it takes out the torque hardly any top end speed lost, but on high grip tracks ull get left for dead buy the 6 cell boys,

[SHY]

I see. Unfortunately those running by ROAR rules must still have that cell in their car as dead weight, as rules over there state 'miniumum 6 cells' (while EFRA stated max. 6). Here up north we don't have high grip tracks, it's very far from 'blue groove' :D

Is it possible to use the slipper as a traction control device on low grip tracks btw? Will it wear out quickly if set very loose? (I know it's mainly intended for saving the driveline from jolts). I tried loosening it a lot on my B4 without really feeling any difference. Same for the X-5, it's slight belt skip helped on the other hand. Anyone experimented with different materials for pucks? (in 1:8 TR we experiment a lot with clutch plates, chlutch bell materials, shimming, springs, load and so on)

[bigred5765]

yeah we leave the dead or unused cell in also, it works well on low grip or loose tracks like in the the states dirt etc,
slipper can be use as a aid but shouldn't really as it kills the pads,but hey every edge helps.
the yokomo white ones are best more controlled slip

[SHY]

Thx! # no for them Yokes? Webshop link? Are there different plates as well? Do they fit both the B4 and X-5?

PS. I added some to my previous posts

PS2. If anyone's looking for upgrades for the XX4 or X-5, I've made a little something here (http://www.ymr.no/x5tuning.htm) to save you from spending 2 months vacuuming RC-forums ;) (make sure you have sound on)

Zzzzzzzzz...

[elvo]

Dude, you tested some seasons ago a 'sectioned' rear wing (like Subaru first thought of I think) - was the difference noticeable?



Not really :o

It's standard in the XXX-CR kit now though...

[SHY]

Hm... I thought it would be just 'fiddling around' yes. I saw some guys use it for 1:8 TR as well, but not anymore...

Subaru rear wing: (for those who haven't seen it)
http://www.tamiya.com/english/products/24276impreza2004japan/index.htm

XXX-CR:
http://www.teamlosi.com/Products/Default.aspx?ProdID=LOSA0032
-a totally new wing with sections, or did they just put a front wing on top of the rear wing to make two extra fins? (saw a local hero do that)

Btw. as I see it a lot of the 1:10 OR cars have quite large drag downforce devices in the front, namely the front shock tower. For instance the S4 and the BJ4 have a quite large area vertical carbon plate in the front.

Elvo my man, as to theory I have a few detail questions:
-will a totally vertical plate generate more downforce than one that is angled (I presume yes)?
-will a vertical plate generate more downforce if the top is totally level as opposed to rounded/other shape? (more 'gurney like')
-will the turbulence from a large area and vertical front shock tower (or wing) decrease the effect of the rear wing? (do a drag downforce device request 'clean air' or can it work with air that's already turbulent?)
-If a vertical plate (wing) provides more downforce than an angled one, how about a plate that's vertical and then at the top bent forward (like a large Gurney)?

A sidetrack:
I btw know a cracy norwegian that used to be a speed windsurfer. He mounted a small wireless camera (normally used on his sail) on his 1:12 car to see how the suspension was working. Did you guys see the Klemm Films onboard video from Vienna? Supercool!!! :cool:

A TOTAL sidetrack:
http://www.oople.com/rc/photos/tiverton2007national/
Elvo, is that our Danny boy? :D

[rich_cree]

I'll give you these two points to discuss amongst you:

1. In 2wd off road the single bigest improvement in laptime tends to come from when you can hook the power up best, i.e. get lots of drive off slow turns (assuming your corner speed, balance or bump handling isn't really bad). In this situation where you have excess power and are having to delicately feed the throttle in, wouldn't extra load on the tyre through extra weight be beneficial to lap time?

2. What if the plastic chassis we use (graphite or plastic stylee) are way stiffer than we need already and the difference in feel is purely down to the shock absorbing characteristics of the material when it physically hits the track surface, i.e. how much energy is returned in the form of a kick, and how much is absorbed (damped) by the material?

[elvo]

2. What if the plastic chassis we use (graphite or plastic stylee) are way stiffer than we need already and the difference in feel is purely down to the shock absorbing characteristics of the material when it physically hits the track surface, i.e. how much energy is returned in the form of a kick, and how much is absorbed (damped) by the material?

Couldn't agree more with that. People talk about flex in absolute terms, but I feel it's more a matter of absorbing energy than of displacement - torsional or otherwise.


And yes, that is "our" Danny Boy :-)


There's a pic on here somewhere of Danny McGee bolting on an almost vertical front wing..flap..pice of lexan. With comments on how it worked. Lemme see if I can find it.

[elvo]

...when it physically hits the track surface,


... or when the shocks "pack up" from hitting a bump or jump at speed.

[rich_cree]

... or when the shocks "pack up" from hitting a bump or jump at speed.

Good shout, never thought of it like that :)

[elvo]

How does that work on the BJ4 BTW? I can't image that graphite flexing or absorbing anything at all. Do you use floppy plastic arms as well? Or is it irrelevant for 4WD?

[rich_cree]

Maybe thats part of the reason XX4 is so good on bumps?

[elvo]

Not only bumps. It's good on anything that is difficult... it drives itself.

[SHY]

are you guys saying that the XX-4 chassis is flexing?

IMHO I think the BJ4 is less stiff. But that the suspension geometry and the weight distribution of the XX-4 is more suitable for rough terrain.

I can tell you from track racing that we use different thickness chassis plates as a tuning aid. A thinner one will reduce weight (which is faster) and provide more grip. A stiffer one is better on high-bite tracks since it makes the car more stable in high speed corners. In general it seems like it for high speed sections is better to have a really stiff chassis and let the shocks do all the work (the Slide alu-car was supreme on highspeed tracks). But on a twisty track you need a much more "lively" car to get response and more steering. A soft chassis and softer plastic arms etc can then be better. Just my 5 cents, maybe not valid for OR...

[Northy]

I'm also of the opinion that the [lastic items are more than stiff enough for our needs for things like wishbones etc, but can see how a plastic tub chassis might be better than a graphite one for some tracks.

The things are still bloody heavy though with all graphite parts! :o

G

[SHY]

As to the material in the wishbones I don't think it's significant in 1:10 OR. AE makes both plastic and graphite parts, and it won't show on laptimes I think. I put on the I&Q "breakaway" front arms on my X-5. Can't get more flexible than that - but it's not noticeable. Just less prone to break.

As to weight I'm surprised that the "StiffAsHell" tubs can actually be lighter than carbon deck chassises...

As to stiffness vs. performance I bet a plastic tub would be just as fast. A bit sceptical though as to axles and bearings living a kinda squeezed life now and then... :o (No prob for 2WD of course I think)

I think for 4WD cars this is why you want the chassis stiff, to make life comfortable for the driveline. Not for better handling per se.

Back to weight: a good way of getting to grips with the facts here would be to test with LiPo cells and see if it's faster or not (when lighter). Anyone tested? (weight must of course be redistributed)

[greeny]

change of subject lol !!!!!!!!!!!!

ive recently changed my losi xxx into a losi xxx mid motor and was wondering shall i make two battery bars for it or will battery tape work??

jordan

[SHY]

Btw is there no cure for this desease??? :o

I want a normal life: get married, watch football on TV, move the lawn, collect stamps, redecorate...

There's no going back now is there?...

[elvo]

Btw is there no cure for this desease??? :o



( o )( o )

[SHY]

LOL! Love U man! (don't take it litterary U sick puppy) :-P

"Doin' time" with my girl and a girlfriend tonite... just about to hit the town... 1:8 TR tomorrow, been a long time... I really like the combo, really the best of 2 worlds!... smelly, fast, flat stuff and silent, bouncy thingy!... :p

[elvo]

"Doin' time" with my girl and a girlfriend tonite... just about to hit the town... really the best of 2 worlds!... smelly, fast, flat stuff and silent, bouncy thingy!...

:o

I went to watch the EC 200mm IC 'B' yesterday. Boy, the fag0try is strong in that class!

[SHY]

There's the "Ladies Cup"... and there's even the "Ladies Cup Electric"...

[elvo]

There's the "Ladies Cup"... and there's even the "Ladies Cup Electric"...


And you've run both? :o

[SHY]

Sure, but I didn't come over to the 'pink side' ;-)

What are you doing watching the Ladies EC then? Wondering about coming out of the closet??? :-P