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Old 10-03-2012, 11:01 AM   #121
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Originally Posted by tomracing View Post
What you are describing here is a shock absorber issue more than a stiffness thing, yes we are looking for a car that gives predictable results but the biggest problem we have with bumps are the shocks.

Chassis flex works as de-coupling of the the front and rear roll stiffness, a car that has a very large Difference in roll stiffness will benefit from the flex to remain stable.
Basically if we are able to better balance our roll stiffnesses front and rear we would need the flex less and be faster, if we cannot achieve balance by either wrong decisions or design flaws we have to work around we would be slower without the flex.

My 2cts
If you look at it this way, yes we need a suspension model that is engineered better. That's a well known fact.

But I was referencing the way it is used in the current crop of cars. Also, even with an almost fully balanced roll stiffness, the flex in the car is still needed to make the car easier to drive. Oleg Babich published a formula on here to find the suspension stiffness on the modern cars in order to compare them to the stiffness of the A700's suspension.

http://dl.dropbox.com/u/43565480/Sus...0Stiffness.pdf

Now, in theory, you could work it out that your front and rear roll centers, camber gains, and suspension stiffnesses, would all be the same. Even with this ability, you would still feel a huge difference and a huge benefit from tuning using chassis flex. This may be a product of the shocks, but that's what we have to work with at the moment.
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Old 10-03-2012, 07:57 PM   #122
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OK so I propose to do some controlled tests to see what we can figure out.

With the suspension setup fixed complete two 5 minute runs using same batteries, motor with the chassis set stiff. Adjust the chassis setup to soft and repeat the test. Runs will be recorded using RC Scoring Pro. We can then look at best 5 , 10 and 20 lap average times to see if there are any noticeable differences.

This may take a while for me to complete as I want run the test for three different suspension setups.

Test Day 1 – Balanced Roll Stiffness. The attached pdf shows RC3 predicted values for a proposed setup. It’s quite close to my current setup so it should work well.
Test Day 2 – Front stiff. Adjust Test 1 setup so the front roll stiffness is 10-20% greater than the rear.
Test Day 3 – Rear Stiff. Adjust Test 1 setup so the rear roll stiffness is 10-20% greater than the front.

What do you think?
Attached Files
File Type: pdf BalancedRollStiffness.pdf (11.3 KB, 159 views)
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Old 10-03-2012, 09:16 PM   #123
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i am interested in what turns up it sounds like a plan <G>
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Old 10-04-2012, 07:15 AM   #124
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yes that is an interesting test to do but only if you can do it in one day, or make sure that the conditions are comparable so that numbers are matching.
if you must test on multiple days make sure to do a baseline run so you at least know if conditions are comparable.

back to the roll stiffness subject it self.
when i wrote about balanced roll stiffness i did not imply that a 50% split will be optimal. In real cars for example a good estimate value seems to be:
%Fwd rollstiffness = %fwd weight distribution + 3% to 5%
so far i've seen mixed results on this for rc cars though i haven't tested this exclusively.
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Old 10-04-2012, 11:27 AM   #125
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I hear you Tom but I'll be doing the test indoor on carpet so test conditions should be the same from day to day. If I can get enough track time to do it all in one day I will but I'm not counting on it.

I will do my best to make sure the tests are run under the same conditions. Anyway what I am hoping to see is if there is a difference between stiff and soft chassis performance for a given setup. I'm not really planning to compare results between the balanced, front stiff and rear stiff suspension setups. If it turns out I can get a comparison there that will be a bonus.
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Old 10-07-2012, 10:00 PM   #126
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the de-coupling thing might be the downside to chassis flex.

the increased tyre contact on bumpy track may be the reason to want some flex.
perhaps bumpy isnt the right word. I just mean surface imperfections that cause reduced tyre contact (slower laptimes) so, an asphalt track.

If the above is true then alot of car setups (generally carpet Vs asphalt) make sense.

Im interested in the results you get Bob thanks for setting that up.
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Old 10-26-2012, 07:43 PM   #127
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Chassis Stiffness Comparison

Sorry for taking so long to get this done but tough to get track time and my day job has been all consuming. Anyway I finally got the track all to myself for the afternoon. I planned to complete all the runs today but unfortunately my rear diff grenaded with three runs left to go. So here is what I have completed so far.

Test 1 – Balanced Roll Stiffness with soft and stiff chassis setting
Test 2 –Front Stiff Roll Stiffness with soft and stiff chassis setting
Test 3 – Rear Stiff Roll Stiffness (this is when my diff grenaded) – to be completed

Test sequence
  • Broke in a new set of tires at the start of the day.
  • The same two batteries were used for the two runs in each car setup.
  • Anti-roll bars were used to change the roll stiffness to keep thing simple. RC3 Setup Summary sheets for Test1/2 are attached if anyone is wants to see exactly what I did.
  • Run duration was approximately 40 laps (about 6 min)

Results
The results recorded using RC Scoring Pro are summarized in the ChassisStiffness1.pdf file. Hopefully the format is self-explanatory. While the sample size is not large the results certainly seem to indicate that the soft chassis setting produced better results. The difference is very small we are talking about hundreths of a second here between the soft and stiff chassis setting but that is what it takes to get to the top of the qualifying order.

Another interesting result from the test so far is that apparently a Front Stiff suspension setup can shave almost .1 sec off my Avg Top 20 lap times. Now I call that significant.
Attached Files
File Type: pdf BalancedSetupSheet.pdf (173.1 KB, 165 views)
File Type: pdf FrontStiffSetupSheet.pdf (173.0 KB, 131 views)
File Type: pdf ChassisStiffness1.pdf (74.3 KB, 172 views)
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Old 11-02-2012, 06:05 PM   #128
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Well I took the afternoon off and completed the Track testing for the final suspension configuration, (rear roll stiffness greater than the front). I used the same procedure as before on basically the same track layout. The track was reset after our Oval Race day so the layout was the same but not all corners were in the exact same position, meaning I can’t directly compare the tests from the two days. That being said the purpose of the tests was to try and see the effect of chassis stiffness on a fixed suspension setup. That I can compare.

The summary of the results for both test days is in the attached file. The disappointing part is the results are completely reversed from Day 1 tests. The Stiff chassis setting produced faster lap times in this round by almost .1 sec. That’s quite a bit more than the difference reported in Day 1. So after almost 500 laps on the same track I am sorry to say I can’t draw a definitive conclusion based on lap time testing.

From a driver’s perspective the difference between the soft and stiff chassis setup was difficult, at least for me, to detect. I did feel that the softer chassis setup was easier to drive but it also seemed less responsive through the tight sections of the track. That may just be what I thought it should feel like though.

I did learn that the front stiff suspension setup works well for me. I ran it at the club race this week with the chassis set soft, finished 2nd. Next week I’m going to the stiff chassis setting and go for the win.
Attached Files
File Type: pdf ChassisStiffness2.pdf (75.4 KB, 114 views)
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Old 11-03-2012, 09:58 AM   #129
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Bob, I'm glad to see that its just not me that can't come up with a conclusive answer to stiff versus soft chassis performance. I can't even remember how many times I've switched back and forth trying to get some sort of trending only to come up with more unknowns. Now add to that changing top decks and again, more variables and more unknowns.

The only thing that seems to work for me on the track is, that the chassis, whether its a stiff or a soft, changing the top deck seems to dictate more performance change than anything. Which is good since its much easier to change the upper than the lower. The interesting thing is that the top deck changes give the same results to me that you saw with the lower deck changes.
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Old 11-04-2012, 03:19 AM   #130
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Yes it is disappointing there was no conclusive winner. On the plus side I did get in lots of practice. Ready for an enduro now.

BTW I was only adjusting the top deck by removing screws. To much work to swap out the lower chassis. Removing screws from the top deck/or swapping out different top plate does make a big difference in the chassis torsional stiffness. I haven't played with changing out the main chassis but based on this test program I'm just going to stick with changing suspension setup. There is enough adjustment there to keep me happy.
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Old 11-22-2012, 08:38 AM   #131
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how do you figure progressive rate springs?
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Old 11-22-2012, 02:45 PM   #132
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The program can only currently handle a fixed spring rate. If you are talking about springs where the coils have two different pitch spacings. Closely spaced at the start and end and wider in the middle then these are what I would call dual rate springs. For small displacements all coils are active which gives you one spring rate. At larger displacements the closely spaced coils will touch making them inactive and only the middle coils will be active.

You can calculate the two different spring rates using the programs Spring Rate Calculator. Just change the number of active coils to determine the difference in the two rates.

Which rate to use will depend on how much displacement the spring will see under maximum cornering loads. Normally I would expect all the coils to be active within the normal handling range where displacements are low. Hitting bumps would be where the starting and ending coils would be bound (touching) so only the middle coils would be active, the higher sping rate.

You can use the Dynamic model to estimate how much displacement the spring will see under cornering. Use the Spring Force versus 'g' graph to determine the spring force at the lateral 'g' level you are interested in. Say it is 8 Newtons. If the spring rate is 2 N/mm then the spring displacement would be 8/2 = 4 mm. If your starting and ending coils are bound at that displacement then use the higher spring rate, otherwise use the lower one.
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Old 11-26-2012, 07:21 PM   #133
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There will a be new version of RC Crew Chief released tomorrow and I just wanted to give everyone a heads up. The new version changes how car files are imported and exported. Car files now include not only the car model but the chassis and setup files as well. So now when you are importing files from the website you only need to download the car file to install a fully functional model. Motor, Battery and ESC models are not included in the car files so when the model is imported these components are set to default models. All the model files on the website will be updated to conform to this format. Setup files will no longer be downloadable as separate files.

This will make sharing of models with your buddies, or even better helping to build the website Library, much simpler.

There are also a number of small improvements and bug fixes that I won't go into here.

This brings me to my plans for the next update. In the next version plans are underway to make numerous improvements plus add some new features (the fun stuff). If anyone has suggestions please feel free to send them through. The only constraint is I am limited to the variables that are included in the current database models. If new variable(s) need to be added to the database to fulfill a request I won't be able to accommodate it.

This is my list so far:

Handling Page
  • Add Track, Wheelbase and CG position adjustment options.
  • Add left turn option
  • Allow Lateral and Longitudinal acceleration values to be changed.
Dynamic page
  • Improve data handling, analysis and display
  • Include provision for comparison of Dynamic Page setup changes to currently selected setup.
  • Add shock dynamic model
CG Calculator
  • Add Cross weight calculation
Motor Manager
  • Include method to enter Dyno Curves to use as source to build Motor Models.

Have a Great Day!
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Old 11-27-2012, 09:49 PM   #134
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ok bob how about a setup or calc for blade type arb ?
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Old 11-28-2012, 01:44 PM   #135
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Quote:
Originally Posted by azeroth View Post
ok bob how about a setup or calc for blade type arb ?
That's a good one I'll add an option to the ARB calculator for blade or straight round bar types.
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