Roll centers

[Dash]

Greetings everyone!
I'm a new member to the site, and have read tons of things off of here.
This year, I am taking over suspension design at my school, and with the help of last years leader, will hopefully make a working suspension.

Anyway, Last year's leader said that we should work on minimizing the lateral movement of the roll center.

So the question I pose is, How much lateral movement is too much movement?

Currently i have a setup that has roughly 1 inch of lateral movement per degree of roll.

Secondly, I've read the articles on roll center height, and it has got me a little confused.

Is there anything wrong with having an underground roll center?

Any help would be greatly appreciated!

[Dash]

Greetings everyone!
I'm a new member to the site, and have read tons of things off of here.
This year, I am taking over suspension design at my school, and with the help of last years leader, will hopefully make a working suspension.

Anyway, Last year's leader said that we should work on minimizing the lateral movement of the roll center.

So the question I pose is, How much lateral movement is too much movement?

Currently i have a setup that has roughly 1 inch of lateral movement per degree of roll.

Secondly, I've read the articles on roll center height, and it has got me a little confused.

Is there anything wrong with having an underground roll center?

Any help would be greatly appreciated!

[exFSAE]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Dash:
Anyway, Last year's leader said that we should work on minimizing the lateral movement of the roll center. </div></BLOCKQUOTE>

Why?

[Dash]

beats the hell outta me!
its a confusing subject....
Most of what i've read just states facts about the height of it, and doesn't mention much of lateral movement....

[edit:] Old leader says it helps limit weight transfer. But I have no idea if thats true or not.

[Pennyman]

Migration and height of the kinematic roll center only gives us an indication of relative instant center location, which is important in finding the ratio of elastic to geometric weight transfer, which has an effect on vehicle predictability.

I suggest these links.

RC 5 pages of glory (http://fsae.com/eve/forums/a/tpc/f/125607348/m/47110403711?r=64510506431#64510506431)

Another good page (http://fsae.com/eve/forums/a/tpc/f/125607348/m/23010668131?r=23010668131#23010668131)

Mitchells ubiquitous myths and realities page (http://www.neohio-scca.org/comp_clinic/hand_out_reprints/Mitchell%20Roll%20Center2007.pdf)

A page from Bill Mitchell's site (http://www.mitchellsoftware.com/ForceBasedRC_1.htm)

[exFSAE]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Dash:
beats the hell outta me!
its a confusing subject....
Most of what i've read just states facts about the height of it, and doesn't mention much of lateral movement....

[edit:] Old leader says it helps limit weight transfer. But I have no idea if thats true or not. </div></BLOCKQUOTE>

The whole premise if your suspension design is being based on his claim of "You gotta limit lateral movement of the RC!" No point of continuing until you can figure out if that's true and why, or if it's a load of crap.

Figure out how RC/IC's set up load transfer and jacking. See for yourself what the effect is of having a RC that is 1, 2, 3 inches, however far away from centerline. Then you can decide if it's a big deal or not.

I'll say this is one topic I don't quite agree with Claude on.

[Dash]

Ok, so basically my mind has been blown.
What the old leader said to me isn't exactly true. By what i've read, I will assume the following:

In summary ( if i am correct ):
1. Kinematic roll center isn't a good tool.
2. Force based roll center is useful.
3. The FAP-cg moment arm length should remain the same in bump/droop. This will help the car keep equilibrium in cornering.

Thanks for the links Pennyman.

Also, Where might i find a program that calculates the force based roll center/FAP?

[Jersey Tom]

I don't think using kinematic roll centers are necessarily bad. I've never seen data to show the difference between kinematic approach using IC's, and force approach. Nor do I know how to calculate a force-based RC. I know how to measure them though!

[Pennyman]

For the most part kinematic roll centers are a pretty good tool to, at a glance, determine if your IC's are doing something wonky (IE shooting into space or something)

[Drew Price]

Dash,

To your reading list I will add two things.

The first are all of Pat Clarke's (design judge) articles. Have all your team mates read them too if you haven't.

http://www.formulastudent.de/a...r/articles/browse/2/ (http://www.formulastudent.de/academy/pats-corner/articles/browse/2/)

Then, read 'Jersey' Tom's F1000 blog from the onset, he has some good observations and explanations of things all in one spot for his own reference that do a good job of summarizing.

http://fsae1000.blogspot.com/


Then read like every post for the last 2 years from Ben, the alum turned Dunlop-race-tire-guy.


http://fsae.com/eve/forums?a=u...tType=1&u=1006073711 (http://fsae.com/eve/forums?a=userposts&s=763607348&sortType=1&u=1006073711)

Best,
Drew