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Old 08-17-2012, 08:55 AM   #91
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I wanted to post up some discussion I had with Bob that might help some other people using the program:
I asked:
On the dynamics page it seems that stiffer = grip, I'm assuming this is just a result of the formula, is there a way to relate weight transfer into that? For instance when I change my spring rate 50% I have to expect xx% less weight transfer to that given corner.
Bob’s response:
Actually softer will develop more grip than stiffer on the basis of Lateral Load Transfer (LLT). If you watch the 'Suspension Dynamics" screencast video on the website and/or read the Dynamic Page Help file LLT is explained in detail there.

A stiffer setup will be more responsive but may have less total grip than a softer setup. The reason being that under the right circumstances the chassis CG will actually drop if you reach the limit of your droop settings in roll. You can see the effect by changing your droop settings and watching the animation carefully or looking at the graph of CG position versus lateral G. When the CG drops the LLT from the inside to outside tires is reduced. A pair of tires with less difference in load between the inside and outside tires will develop more grip.
Dynamics Youtube video:
http://www.youtube.com/watch?v=G6n1d1g0_qE&feature=plcp

Next I asked about chassis roll:
In the roll angle vs Lat G graph you have about 3dg of roll, if my maths are right a normal TC at 5.5 ride height and a 90mm chassis should have almost 7dg before contact is made (triangulating the plane under the chassis) I'm not sure what you are using for the dg of roll measurement.
Bobs response:
Regarding the chassis roll question. The roll versus lateral g graph shows how much the chassis rolls at the maximum lateral g value entered. The simulation rolls the chassis about the dynamic roll centre until the maximum g level entered is reached. If you want the chassis to roll more enter a higher lateral g value in the box. The simulation will run until the lateral g valu7e entered is reached or the chassis contacts the ground whichever comes first. Your 7 deg calculation is correct for chassis roll about the mid point of the chassis. The maximum roll angle achievable will be different when rolling about the roll centre and with droop effects considered.

I admit that I never read the help page in the program, but I looked at it, and it is very helpful, for example:

Lateral Load Transfer (LLT) versus Lateral g – LLT is the amount of load that is
transferred from the inside wheels to the outside wheels during cornering.

So to minimize the LLT you want to reduce the car weight, lower the CG or increase the
track width. Ok so why would you want to reduce the LLT. The reason is tires. Consider
two load cases with tire pairs both carrying the same total loads. In the first case the
tires carry close to the same load (low LLT) and in the second case the tires carry
significantly different loads (high LLT). Because of the way tires convert vertical load
into lateral grip the tires with similar loads in case 1 will produce more grip than case 2.
(couldn’t paste the pictures).
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Old 08-17-2012, 08:18 PM   #92
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Just uploaded a TRF417 model that includes Gilles Groskamp's setup from the Worlds. It would be worth downloading the model and setup even if you don't run the 417X.

It can only help to see where the pros run their chassis setup. Files are on the model download page on the website.
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Old 08-17-2012, 09:01 PM   #93
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Bob,

You may have answered this, does your application take into account chassis flex? If yes, how do you enter this data? Can it take into account removing top deck screws, ect as well?

I'm on he cusp of buying this app with the addition of the new Suspension dynamics module. Any hints to what's coming in the near future?
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Old 08-17-2012, 11:19 PM   #94
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Bob, what if I ran my car unbalanced from left to right, with most of the weight on the right side. Would that give me an advantage if all the fast turns were right turns, and slow turns were left turns? I noticed I could really go faster in right turns unbalanced than balanced side to side.... Most US tracks have lots more fast right turns than left ones...
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Old 08-18-2012, 05:47 AM   #95
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Quote:
Originally Posted by bkspeedo View Post
Bob,

You may have answered this, does your application take into account chassis flex? If yes, how do you enter this data? Can it take into account removing top deck screws, ect as well?

I'm on he cusp of buying this app with the addition of the new Suspension dynamics module. Any hints to what's coming in the near future?
At this point the program does not take into account chassis torsional stiffness and potential adjustments that can be made. The math gets much more complicated when you include that variable. I have some ideas on how it could be incorporated into the program but I would have to build a test fixture to measure the torsional stiffness. I doubt it could be calculated accurately enough when you consider all the variables. Long story short it could happen but no promises.

Next upgrades will be to the dynamics module to allow setup changes to be compared head to head. I'm hoping to include better graphics to help with visualization. Following that I'm thinking of adding shock dynamics and damping module. That's about as far ahead as I have planned.
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Old 08-18-2012, 05:59 AM   #96
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Quote:
Originally Posted by bertrandsv87 View Post
Bob, what if I ran my car unbalanced from left to right, with most of the weight on the right side. Would that give me an advantage if all the fast turns were right turns, and slow turns were left turns? I noticed I could really go faster in right turns unbalanced than balanced side to side.... Most US tracks have lots more fast right turns than left ones...
You have a good point. With most on-road tracks that run clockwise you will always have more right hand turns than left. If you look at it in oval terms they always talk about 4 turns (even if there are only two really) to get around the track. So that means if you assume 90 deg turns there will be 4 more right turns than left to complete 360 degrees. If you set you car up with more right side weight it may provide an advantage overall in the right turns. Would definitely take some experimentation but would certainly be worth a try.
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Old 08-18-2012, 09:17 AM   #97
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Thanks....Bob....
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Old 08-18-2012, 10:15 AM   #98
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Quote:
Originally Posted by BobW View Post
At this point the program does not take into account chassis torsional stiffness and potential adjustments that can be made. The math gets much more complicated when you include that variable. I have some ideas on how it could be incorporated into the program but I would have to build a test fixture to measure the torsional stiffness. I doubt it could be calculated accurately enough when you consider all the variables. Long story short it could happen but no promises.

Next upgrades will be to the dynamics module to allow setup changes to be compared head to head. I'm hoping to include better graphics to help with visualization. Following that I'm thinking of adding shock dynamics and damping module. That's about as far ahead as I have planned.
Thanks Bob, I figured chassis flex would be very difficult to simulate.

Given your engineer background and suspension dynamics research how much do your feel chassis flex plays into setup and is there a way to approximate flex into your calculations?
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Old 08-18-2012, 08:37 PM   #99
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If you were to ask me today to design a new chassis I would likely start with a chassis torsional stiffness that would be high enough that you would neglect it in the suspension design. As you can imagine there are enough variables to deal with that eliminating one makes the job somewhat easier. That is what conventional Race Car Design theory would recommend.

Honestly I don't have an answer as to how much effect changing the chassis torsional stiffness has on handling. As a guess I would expect the torsional stiffness of the chassis to be 10 times that of the suspension. That would mean 90% of the handling is suspension and 10% is chassis. If you can change the chassis stiffness by say 10% then that would have a 1% effect on the overall chassis + suspension stiffness. Not huge but possibly significant. Keep in mind I'm just guessing here.

My personal opinion is you don't want to use a uncontrolled spring to adjust the handling of your car. That is essentially what the torsional stiffness of a chassis is, a spring. If you don't have a damper (shock) to control it you risk going unstable if the chassis stiffness is close to the suspension roll stiffness. I prefer to use known quantities like springs, shocks, ARB's and roll centres to adjust the handling.
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Old 08-18-2012, 08:48 PM   #100
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Quote:
Originally Posted by BobW View Post
If you were to ask me today to design a new chassis I would likely start with a chassis torsional stiffness that would be high enough that you would neglect it in the suspension design. As you can imagine there are enough variables to deal with that eliminating one makes the job somewhat easier. That is what conventional Race Car Design theory would recommend.

Honestly I don't have an answer as to how much effect changing the chassis torsional stiffness has on handling. As a guess I would expect the torsional stiffness of the chassis to be 10 times that of the suspension. That would mean 90% of the handling is suspension and 10% is chassis. If you can change the chassis stiffness by say 10% then that would have a 1% effect on the overall chassis + suspension stiffness. Not huge but possibly significant. Keep in mind I'm just guessing here.

My personal opinion is you don't want to use a uncontrolled spring to adjust the handling of your car. That is essentially what the torsional stiffness of a chassis is, a spring. If you don't have a damper (shock) to control it you risk going unstable if the chassis stiffness is close to the suspension roll stiffness. I prefer to use known quantities like springs, shocks, ARB's and roll centres to adjust the handling.
Unfourtunately rubber tire TC's have proven flex to be an integral, and in some cases essential to a well performing car. If you look at many of the changes the top cars are making these days they revolve around flex. I can say that running 4 screws vs 6 in the rear part of the top deck of my T3 yeilds a different change than what can be achieved with a spring, link or droop change.
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Old 08-18-2012, 09:57 PM   #101
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Thank you again for your insight. Back in he day when foam tires where popular for carpet racing the chassis was not used as much as a tuning aid like they are today due to there stiffness.

The TOP EX is probably the softest chassis car I've seen to date without buying a conversion and I'll have to say it can be a handful on high grip. I've been experimenting with setup features I've never tried before to make the car consistent from the beginning of race to the end as the tire grip changes. So far i have not found the magic formula but i think i'm getting close. This is what intrigues me about this app, it can probably teach me a few things and come to a conclusion faster versus hours of experimentation.
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Old 08-19-2012, 06:27 AM   #102
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Don't get me wrong I'm not saying chassis flex doesn't have a role. Personally I haven't played with chassis stiffness much. I have always used suspension settings to adjust handling.

At somepoint I'll have a look at chassis stiffness effects I just can't say when. For now RC3 just deals with shocks, springs, ARB, Roll centre, camber gain and droop. The nice thing about using a setup simulation is you can look at the effect of many different changes very quickly. It has helped me for sure.
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Old 08-19-2012, 07:48 AM   #103
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Chassis flex only seems to be desirable when grip is at a premium. Looking at real world race cars, F1 cars with tons of grip run super stiff chassis while a dirt oval car is intentionally much more flexible. When TC ran on foam, they had fairly stiff chassis but with rubber, softer seems to be better.

Of course, a lot of the reason for this has nothing to do with ultimate performance. In theory, a stiff chassis should always be better but in our RC world, it is virtually impossible to get everything exactly right. We just don't have the fine adjustability, hyper accurate set-up tools and proper shocks to get a setup spot on. Plus, very few RC racers have the knowledge and experience of a professional race engineer. We also don't have a butt in the seat to give precise feedback on what the car is really doing or telemetry to give us data. This is where flex comes in big. Flex disguises other set-up problems. A flexible car has a HUGE sweet spot it will work in set-up wise. It will also be less effected by changes in condition such as weather, grip level, tire type and condition, etc. So a flexible car will still work reasonably well with a sub-optimal set-up. It will NEVER work as well as a stiff car with a PERFECT set-up but with all the limitations I described, a perfect set-up is virtually impossible for us to ever attain.
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Old 08-19-2012, 08:45 AM   #104
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Well said Wingracer.

I been looking at a some of the pro setups lately and comparing the differences between their asphalt and carpet setups. I was expecting to see big differences but surprisingly the ones I've looked at so far have been very similar. One needs to factor in that the tracks they run are well prepped, smooth and generally with high grip. Maybe it isn't so surprising. If you haven't tried this yet download an asphalt and carpet setup from the same driver from the website and compare for yourself.

The other interesting thing to try is comparing differences between chassis manufacturer's with all the marketing hype stripped away.
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Old 08-19-2012, 09:32 PM   #105
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Default GP chasis

Hi Bob...

Im very interesting with your SW.....could it be used for GP chasis car?
because right know I'm using X ray Nt1 and Agama EVo8 for my racing gear...and hopefully can use the SW for my Setup...

Regards..
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