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Mid-motor touring cars. Legit faster or fad?

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Mid-motor touring cars. Legit faster or fad?

Old 09-16-2019, 06:02 PM
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Originally Posted by glennhl View Post
Can anyone tell me the roll stiffness of the chassis flex versus the roll stiffness of the spring/ARB's? Just curious of how much chassis flex are we talking about here?
This is something.. I've been working on quantifying. Sadly, life has kept me busy.
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Old 09-16-2019, 07:42 PM
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Originally Posted by Nerobro View Post
This is something.. I've been working on quantifying. Sadly, life has kept me busy.
If you use the Hudy tweak station you can introduce an exact displacement at each corner of the car and watch for lift. You can work backwards from that or add scales to the mix. I only needed to compare one chassis to another that were otherwise identical so force per mm wasnt needed but scales and ride height gauges under the tweak station would probably do it for you.
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Old 09-16-2019, 07:47 PM
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Originally Posted by MaxRain View Post
One thing that I have noticed with using a stiff chassis (T3 - EU) is that the suspension has to work much harder, meaning overall it has more movement. This does not make a car slower, but harder on tires. Knowing how to adjust the cars roll stiffness by way of roll centre and weight transfer is key and important to ensure that grip is at the correct level, so that you can maximize corner speed and match track conditions.

The challenges with a stiff chassis, is that I found that a suspension can take quite a beating, and may require filling shocks more often because they leak shock oil. If a shock(s) start leaking (as most commonly do), they get unbalanced left to right, and the result is that you will likely be slower. This is where a racer needs to check and rebuild shocks regularly.

If you have a flex chassis, I believe it can hide / compensate for leaky shocks, and possibly compensate for a wheel that is unbalanced.
Put an unbalanced wheel on a stiff chassis i.e. front left, and it is likely that the front right end of the chassis will be affected by the vibration. The unbalanced wheel will also add unwanted movement to the suspension (high freqency oscillations), and could cause a shock to leak prematurely. The faster a car travels down a straight with an unbalanced tire, the higher amounts of vibration will occur resulting in loss of contact patch. Top level drivers pay attention to this by "listening" to the feel of the car while it is on the track, or they can visualize what is happening by placing themselves inside the car.

Basically, I see flex as a way to put a band-aid on a bad suspension setup, as it takes time to learn what works to match track conditions with different ambient temperatures.
If you don't have the time or patience to play with shock settings, or don't take the time to experiment with shocks, you will never know how good a chassis can really be for your driving style.
good observations there. I concur.
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Old 09-16-2019, 11:31 PM
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Originally Posted by Bry195 View Post


If you use the Hudy tweak station you can introduce an exact displacement at each corner of the car and watch for lift. You can work backwards from that or add scales to the mix. I only needed to compare one chassis to another that were otherwise identical so force per mm wasnt needed but scales and ride height gauges under the tweak station would probably do it for you.
Relative measurements are not useful to others. :-) I want.. quantative measurements that we can share and compare with. At least, that's my plan.
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Old 09-16-2019, 11:37 PM
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Originally Posted by Nerobro View Post
Relative measurements are not useful to others. :-) I want.. quantative measurements that we can share and compare with. At least, that's my plan.
You want RC Crew Chief
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Old 09-16-2019, 11:52 PM
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Originally Posted by daleburr View Post
You want RC Crew Chief
No, I do not. I want to be able to generate the data to put INTO RC Crew Chief.
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Old 09-17-2019, 04:11 AM
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Originally Posted by glennhl View Post
Can anyone tell me the roll stiffness of the chassis flex versus the roll stiffness of the spring/ARB's? Just curious of how much chassis flex are we talking about here?
Let's be more precise in terms. "The roll stiffness" in my translation is how the car reacts (rolls, tilts) on the lateral load applied to the CG.
But the car with torsionally flexible chassis gets exactly the same total lateral roll (displacement of CG point) as the car with 100% stiff chassis at the same lateral load.
So "the roll stiffness of the chassis flex" is not correct term at least in my translation. Probably do you mean something different?
It has sense to consider the reaction of the particular corner suspension on the load applied to the wheel of this car's corner. Let's consider only the vertical load now. And let's consider the additional vertical load on the particular wheel that can be caused by roughness and non-flatness of the track. We know that our RC tracks are not 100% flat and smooth especially the asphalt tracks.
For sure the torsional flex of chassis makes the reaction of the particular suspension softer and the sway bar makes this reaction stiffer.
On Awesomatix cars the chassis flex makes the reaction of suspension softer from ~ 8% for our stiff alloy lower deck to ~28% for our carbon lower deck in our best setups. Also it is interesting to note that the mostly used swaybars make the reaction of suspension stiffer back on ~8..12%.
So the main conclusion: the chassis torsional flex makes the car suspension softer against the roughness and non-flatness of the track but doesn't affect on the total lateral roll in turns. This is a reason of why the cars with optimal level of flex can have more grip at conditions of real non-ideal flat and smooth RC track.
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Old 09-17-2019, 04:21 AM
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Originally Posted by Oleg Babich View Post
Let's be more precise in terms. "The roll stiffness" in my translation is how the car reacts (rolls, tilts) on the lateral load applied to the CG.
But the car with torsionally flexible chassis gets exactly the same total lateral roll (displacement of CG point) as the car with 100% stiff chassis at the same lateral load.
So "the roll stiffness of the chassis flex" is not correct term at least in my translation. Probably do you mean something different?
It has sense to consider the reaction of the particular corner suspension on the load applied to the wheel of this car's corner. Let's consider only the vertical load now. And let's consider the additional vertical load on the particular wheel that can be caused by roughness and non-flatness of the track. We know that our RC tracks are not 100% flat and smooth especially the asphalt tracks.
For sure the torsional flex of chassis makes the reaction of the particular suspension softer and the sway bar makes this reaction stiffer.
On Awesomatix cars the chassis flex makes the reaction of suspension softer from ~ 8% for our stiff alloy lower deck to ~28% for our carbon lower deck in our best setups. Also it is interesting to note that the mostly used swaybars make the reaction of suspension stiffer back on ~8..12%.
So the main conclusion: the chassis torsional flex makes the car suspension softer against the roughness and non-flatness of the track but doesn't affect on the total lateral roll in turns. This is a reason of why the cars with optimal level of flex can have more grip at conditions of real non-ideal flat and smooth RC track.
Thanks Oleg for stepping in - and congrats for obviously making it work on your creations, btw.

Are you saying that, on a perfectly smooth/flat track, flex would be useless? I guess not, because there are some torsional forces caused by speed variations (so longitudinal accelerations) while the car is turning (lateral acceleration), correct?

If you'd care to stick around in this thread, I think you could help de-mystify a lot of the "tribal knowledge" (love that term above!!!) that has polluted RC cars setup theory for ages now...

thanks in advance
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Old 09-17-2019, 04:49 AM
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Originally Posted by Lonestar View Post
Thanks Oleg for stepping in - and congrats for obviously making it work on your creations, btw.
Are you saying that, on a perfectly smooth/flat track, flex would be useless? I guess not, because there are some torsional forces caused by speed variations (so longitudinal accelerations) while the car is turning (lateral acceleration), correct?
If you'd care to stick around in this thread, I think you could help de-mystify a lot of the "tribal knowledge" (love that term above!!!) that has polluted RC cars setup theory for ages now...
thanks in advance
Yes, even on a perfectly smooth/flat track some flex probably can be usefull also. This is also due to the car with the turned front wheels is not 100% flat itself. Due to the caster and the wheel axel offset the outer wheel goes up and the inner wheel goes down at turning. The car becomes a bit "tweaked" and the chassis flex can compensate this maybe with better result compare to the springs of suspension.
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Old 09-17-2019, 06:26 AM
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Default Rebellion mid motor

Hi first time on here has anyone used the rebellion rc mid conversion and how did you find it. Thank you.
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Old 09-17-2019, 06:26 AM
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Originally Posted by Bry195 View Post


good observations there. I concur.
Thanks.
A secondary method to justify how good a suspension setup is would be tire temperature. Which was inspired with your post about thermal imaging. After reading that string of posts, I asked Bob (rc crew chief) if tire temperature could be incorporated into the software and he responded that he is going to consider it.
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Old 09-17-2019, 09:27 AM
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Originally Posted by Oleg Babich View Post
Let's be more precise in terms. "The roll stiffness" in my translation is how the car reacts (rolls, tilts) on the lateral load applied to the CG.
But the car with torsionally flexible chassis gets exactly the same total lateral roll (displacement of CG point) as the car with 100% stiff chassis at the same lateral load.
So "the roll stiffness of the chassis flex" is not correct term at least in my translation. Probably do you mean something different?
It has sense to consider the reaction of the particular corner suspension on the load applied to the wheel of this car's corner. Let's consider only the vertical load now. And let's consider the additional vertical load on the particular wheel that can be caused by roughness and non-flatness of the track. We know that our RC tracks are not 100% flat and smooth especially the asphalt tracks.
For sure the torsional flex of chassis makes the reaction of the particular suspension softer and the sway bar makes this reaction stiffer.
On Awesomatix cars the chassis flex makes the reaction of suspension softer from ~ 8% for our stiff alloy lower deck to ~28% for our carbon lower deck in our best setups. Also it is interesting to note that the mostly used swaybars make the reaction of suspension stiffer back on ~8..12%.
So the main conclusion: the chassis torsional flex makes the car suspension softer against the roughness and non-flatness of the track but doesn't affect on the total lateral roll in turns. This is a reason of why the cars with optimal level of flex can have more grip at conditions of real non-ideal flat and smooth RC track.
As usual, you are a wealth of outstanding information. Thank you for this. I'll try to make my point by taking it to the limit. When I stiffen or soften one end or the other using the springs/ARB's, I change the amount of weight transfer on each end. The softer end has less weight transfer than the stiff end and therefore the soft end ends up with more traction than the stiff end. For me, this is my main tuning tool. Now lets say I go to the softest chassis possible (in torsion). I put a gimble in the middle and the chassis is free to rotate. Now both ends will transfer the same amount of weight (assuming 50/50 weight transfer) and now my tuning tool will no longer work. Since the chassis is gimbled, the soft end and stiff end will transfer the same amount of weight but the soft end will roll further. But the soft end will still end up with the same amount of traction as the stiff end.
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Last edited by glennhl; 09-17-2019 at 09:38 AM.
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Old 09-17-2019, 09:33 AM
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Originally Posted by Nerobro View Post
Relative measurements are not useful to others. :-) I want.. quantative measurements that we can share and compare with. At least, that's my plan.
i gave you 2 methods. The one I used was relative and just based on displacement.

The second method is done the same way springs are done or you can consider it empirical.A force over a distance. Yield or gradient or slope of force or torque over distance. Or an average of the five over distance. Ride height gauge and mass scale.

Actually both are empirical if you understand your chassis mass and dimensions as well as the force you introduce to create the slope of torque/distance. Itís just not something I want to describe.
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Old 09-17-2019, 09:50 AM
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Originally Posted by MaxRain View Post


Thanks.
A secondary method to justify how good a suspension setup is would be tire temperature. Which was inspired with your post about thermal imaging. After reading that string of posts, I asked Bob (rc crew chief) if tire temperature could be incorporated into the software and he responded that he is going to consider it.
average front/rear temp or right/left side. There is probably 20 ways to look at the data per point on a specific tire and averages over groups that are eye opening.

It was interesting that I found a chassis that would flex in right hand turns but not left hand from tire temperature data.

thanks
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Old 09-17-2019, 10:37 AM
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Originally Posted by glennhl View Post
As usual, you are a wealth of outstanding information. Thank you for this. I'll try to make my point by taking it to the limit. When I stiffen or soften one end or the other using the springs/ARB's, I change the amount of weight transfer on each end. The softer end has less weight transfer than the stiff end and therefore the soft end ends up with more traction than the stiff end. For me, this is my main tuning tool. Now lets say I go to the softest chassis possible (in torsion). I put a gimble in the middle and the chassis is free to rotate. Now both ends will transfer the same amount of weight (assuming 50/50 weight transfer) and now my tuning tool will no longer work. Since the chassis is gimbled, the soft end and stiff end will transfer the same amount of weight but the soft end will roll further. But the soft end will still end up with the same amount of traction as the stiff end.
I have been told, the flex of different chassis components is mainly used when the changes you need to do in principle by changing springs/sway bars/roll centers are so subtle that can not be reliably managed (due to tolerances etc.).
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