Suspension travel

[clausen]

How much do you people have?

I know about the one inch either direction rule.

I've seen a lot of cars that cant be much more than an inch off the ground, so I'm guessing that's all they're running.

Regards

Paul Clausen
Uni of Adelaide

[clausen]

bump

Regards

Paul Clausen
Uni of Adelaide

[Big Bird]

Hi Paul,

I'm amazed that everyone is so secretive about this one. For what it is worth, we are running the minimum 2 inches this year, as have done previously. One of the cars showed up at the Oz event with something like 5 inches a couple of years back, and were caned by the judges. Since FSAE tracks (generally!) don't have kerbs/bumps/potholes, we don't need to design for one wheel bump - therefore the bare minimum should be enough to control roll and pitch loadings.

Also the more suspension travel you have, the harder it is to control cambers, bump steers, roll centres etc. throughout the whole range of movement.

That's our thoughts, anyone can jump in and shout us down if they like. Hope all is going well in Adelaide, you are going to have to show us all the good pubs when we get there in December!

Cheers,

Geoff Pearson
RMIT FSAE 2003

Design it. Build it. Break it.

[ben]

<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>Originally posted by Big Bird:
Since FSAE tracks (generally!) don't have kerbs/bumps/potholes, we don't need to design for one wheel bump - therefore the bare minimum should be enough to control roll and pitch loadings.
<HR></BLOCKQUOTE>

I'm glad you put generally in there. You wouldn't want to run on the FStudent enduro course without having designed for a bump case!

Ben

University of Birmingham
www.ubracing.co.uk (http://www.ubracing.co.uk)

[Frank "Ruska"]

You never saw the Formula Student Track in UK. I know the Australian tracks from the last 2 years. And for Uk you need a car which is designed for bump! 3 different surfaces in the enduro. We test our car on a very clean surface here in germany. afetr 1 lap in autocross our driver get out of the car and said: "what kind of sxxx is this, thats not a racetrack it is something else"

Frank Röske
Student Racing Team
University of Applied Sciences Stralsund/Germany

www.student-racing.de (http://www.student-racing.de)

[awhittle]

A few basic rules

1) At full droop the spring should sill be in top and bottom spring seat but just bairly. ie. no preload and never rattling.

2) You need to be in the .5 motion ratio range or the shock will not be travling enough on normal surfaces to meter the movement

3) Most bike shocks have about 2" of total travel

4) This all gives about 4" of total wheel travel at the tire

5) You will end up with about 1" droop and 3" of compression total

6) You need about 1.5 to 2" of chassis ground clearance to deal with dips and bumps at full cornering when you happen to hit that bump, it all works out about right.

7) Life is too short to learn rising rate rockers. Shoot for about linear motion ration throuout the entire 4" of travel.

8) Make the motion ratio adjustable to correct for errors in calcs and assumptions. You will need it.

9) Use the spring that came with the shock or the valving will not be in the adjustable (sweet spot) of the shock. A shock designed for a 200# spring will never deal with a 1000# spring. A 20% change would not be a concern

The book by Alan Stanaforth and his way of calcing all this will piont to about 2-3 cycles/sec for a car of this type

Hope this helps

AW

[Mick_P]

Along AW's lines I agree. It really all depends on what you design your suspension to do. 1 inch droop may be good for a certain system, but 2 inches may be better for another.

It seems to be the norm where 3 - 4 inches total travel is seen.

Mick Partridge
Swinburne University of Technology

[Frank]

40mm ground clearance

2.8 hz front
3.2 hz rear

1535mm wb
310mm CG

300 kg total weight

we've only hit the ground at the hillclimbs (really bumpy surface)

[wacko]

<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>Originally posted by Frank:
40mm ground clearance

2.8 hz front
3.2 hz rear

1535mm wb
310mm CG

300 kg total weight

we've only hit the ground at the hillclimbs (really bumpy surface)<HR></BLOCKQUOTE>

am i mistaken .. but arent most cars designed with higher front frequency?

[Schumi_Jr]

Most production cars are designed with higher front frequencies to prevent the car from pitching over bumps. As far as I know this more important for ride quality than for handling (thus is a rule of thumb for passenger cars not necessarily racecars).

Aaron Johnston
University of Waterloo FSAE

www.eng.uwaterloo.ca/~fsae (http://www.eng.uwaterloo.ca/~fsae)

[Schumi_Jr]

wow, what I said was totally wrong. I shouldn't be allowed to post anything after 9pm. Running higher REAR frequencies prevents pitching. The rear "catches up" to the front giving a flatter ride.

Aaron Johnston
University of Waterloo FSAE

www.eng.uwaterloo.ca/~fsae (http://www.eng.uwaterloo.ca/~fsae)

[wacko]

<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>Originally posted by Schumi_Jr:
wow, what I said was totally wrong. I shouldn't be allowed to post anything after 9pm. Running higher REAR frequencies prevents pitching. The rear "catches up" to the front giving a flatter ride.

Aaron Johnston
University of Waterloo FSAE

http://www.eng.uwaterloo.ca/~fsae<HR></BLOCKQUOTE>


i see ... always had the notion of a higher front frequency as stated in Milliken. are there any ways to get a rough frequency figure besides Millikens "ride natural frequency vs static wheel deflection" charts?

[Schumi_Jr]

That's actually from Milliken, both in the "Chassis Design" book and in RCVD in the Damper chapter. By "frequency figure" do you mean "how do you know what natural frequency to run?". As far as I know your ride natural frequency should be as low as possible for a given amount of suspension travel. Your ride height should be as low as possible for cg effects, but you will have to run a higher frequency, thus are sacrificing grip. Yet again vehicle dynamics answers our questions with a question. In my opinion the best way to answer this is to test different combinations. I am embarresed to say that our team doesn't have very well documented testing on this, but I aim to change that very soon. As far as our car... well we don't have stiff enough springs to run frequencies as high as Frank and our ground clearance is lower.

Aaron Johnston
University of Waterloo FSAE

www.eng.uwaterloo.ca/~fsae (http://www.eng.uwaterloo.ca/~fsae)

[wacko]

<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>Originally posted by Schumi_Jr:
That's actually from Milliken, both in the "Chassis Design" book and in RCVD in the Damper chapter. By "frequency figure" do you mean "how do you know what natural frequency to run?". As far as I know your ride natural frequency should be as low as possible for a given amount of suspension travel. Your ride height should be as low as possible for cg effects, but you will have to run a higher frequency, thus are sacrificing grip. Yet again vehicle dynamics answers our questions with a question. In my opinion the best way to answer this is to test different combinations. I am embarresed to say that our team doesn't have very well documented testing on this, but I aim to change that very soon. As far as our car... well we don't have stiff enough springs to run frequencies as high as Frank and our ground clearance is lower.

Aaron Johnston
University of Waterloo FSAE

http://www.eng.uwaterloo.ca/~fsae<HR></BLOCKQUOTE>

isnt that always the problem haha.. dymanics are quite an ass without ever getting the best answer... as for stiff springs wat are ur calculated spring stiffness?. .. for our car based on 300kg and abt 500lb/in for tire rate with close to 1:1 crank ratio we seem to need abt a 2.6 kg/mm spring which again seems kinda soft compare to other teams...

the original springs that come with our R1 dampers we might be using are ard 8.9 kg/mm which are terribly hard, so customised springs seem to be the only way.

[clausen]

<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>Originally posted by wacko:
[QUOTE]Originally posted by Schumi_Jr:


the original springs that come with our R1 dampers we might be using are ard 8.9 kg/mm which are terribly hard, so customised springs seem to be the only way.<HR></BLOCKQUOTE>


R1 dampers as in YZF R1 dampers?

Regards

Paul Clausen
Uni of Adelaide

[wacko]

yap .. anyone with experience using those? they are rather cheap and available compared to mountain bike shocks

[clausen]

wacko,

Who are they made by?

Do you know anything about revalving them?

Regards

Paul Clausen
Uni of Adelaide

[wacko]

<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>Originally posted by clausen:
wacko,

Who are they made by?

Do you know anything about revalving them?

Regards

Paul Clausen
Uni of Adelaide<HR></BLOCKQUOTE>

not sure who the manufacturer is.. and not too concerned in the mean time about revalving them... so wat kinda frequencies and springrates u guys running?

[ben]

<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>Originally posted by wacko:
isnt that always the problem haha.. dymanics are quite an ass without ever getting the best answer... as for stiff springs wat are ur calculated spring stiffness?. .. for our car based on 300kg and abt 500lb/in for tire rate with close to 1:1 crank ratio we seem to need abt a 2.6 kg/mm spring which again seems kinda soft compare to other teams...
<HR></BLOCKQUOTE>

2.6 kg/mm (25.5N/mm) seems fine to me. Many teams I saw at FStudent were running very hard. I'll admit I initially spec'd our springs too hard and softened them up considerably during our test program.

Ben

University of Birmingham
www.ubracing.co.uk (http://www.ubracing.co.uk)

[Amos]

Slightly unrelated, but still in the suspension realm..... does anyone have experience with running torsion bars instead of springs???
cheers

If it aint broke, still fix it!.... you'll do a better job.

[Jarrod]

I have some experience with torsion bars from working on sprintcars - general feeling is that coil springs 'pogo' too much, very hard to drive. A torsion bar of equivalent stiffness give better feel. not sure of the mechanism that makes it so, but guys with first hand experience will swear to it. Obviously this is a very different situation to FSAE. I may be biased, but radius rods and torsion arms look cool too.

[karter]

Sprint cars use torsion bars to lenghten the "spring base" of the car. I'm not sure what that means, seems like if the chassis is stiff enough that it wouldnt matter where the springs hook to. Rember that a coil spring is simply a wound torsion bar! I suspect the real reason is ease of repair and light weight. World of Outlaw teams would spend thousands of dollars on titanium bolts to save weight.

[apoorav1989]

we are dng fsae for the first time.....so should we use torsion bars...and also wat are its advantages..

[flavorPacket]

I would recommend candy bars instead of torsion bars. Much cheaper and more delicious than 18 Ni maraging steel...

[STRETCH]

Originally posted by awhittle:
A few basic rules

6) You need about 1.5 to 2" of chassis ground clearance to deal with dips and bumps at full cornering when you happen to hit that bump, it all works out about right.

7) Life is too short to learn rising rate rockers. Shoot for about linear motion ration throuout the entire 4" of travel.

8) Make the motion ratio adjustable to correct for errors in calcs and assumptions. You will need it.

AW

Harkin back to the original question, I'd say a lot of teams run with a GC barely above minimum, as you can control pitch and roll with a stiff setup. Constant motion ratios is a definite, purely to keep things predictable and linear for the driver.

As for frequencies, I've read in a number of places that its not important at all for these race cars. Surely its more important to get your spring rates/motion ratios right to get the most out of your damper, and attain adequate ride/roll stiffness. The frequency you end up with won't affect much on these cars. Also, in road cars it's the REAR natural frequency that will be higher, to damp out pitch oscilations from a bump input. See Gillespie page 177.

[Pennyman]

Talk about bump...in more ways than one!