Anti roll bar

[Cement Legs]

Is the main reason for using an anti-roll bar to help minimize the migrataion of the roll center? If so what others considerations should be taken in designing one? Does anyone have pictures?

[Cement Legs]

Is the main reason for using an anti-roll bar to help minimize the migrataion of the roll center? If so what others considerations should be taken in designing one? Does anyone have pictures?

[D J Yates]

The primary purpose of an ARB is to increase the roll stiffness and hence reduce body roll. If your roll center migrates during roll, then yes an anti-roll bar will reduce the lateral migration. However, i'm sceptical about kinematic roll centers and have no idea how a force based roll center moves laterally.

Secondary purpose: by using an adjustable ARB at the front and rear, you can adjust the distribution of the roll stiffness. This has an effect on the lateral load transfer and should (i've never had the chance to practice the theory) allow you to tune the car.

The downside to an ARB is that it links the wheels, creating a dependence in what is otherwise independent suspension. I mentioned this when queryig the use of monoshocks (another thread that no one replied to - come on guys). Think of one wheel bump as a combination of roll and ride such that one wheel moves and the other stays in the original position. Since the anti-roll bar will resist the roll, it will be resisiting one wheel bump also. If you had an infintely stiff roll bar then everytime you hit a bump your ARB will resist the roll and launch the car right over it. eg. F1 cars riding the curbs.

Of course, the other issue with an anti-roll bar is damping.

Before i'd realised and understood all of the above, i thought that if i used a really stiff ARB then i wouldn't have to worry about roll center migration in my design. Unless your driving on a perfectly smooth surface this isn't a good idea. Now i know better...but i still don't worry too much about the RC.

[Angry Joe]

http://www.we-todd-did-racing.com/wetoddimage.wtdr?i=wNzY2NTg2NnM0MTNkZmQzMXk1NDE%3D

Ours was primarily a quick tuning tool.

[Marc Jaxa-Rozen]

On a related note, what kind of diameters are you guys using? I know this depends on a myriad of factors, but our 2004 car had 3/4" OD x .065 bars front and rear- and after rechecking the calculations, I can't see how they could have provided anything less than an outlandishly high stiffness.

RCVD and ADAMS give me something pretty close to 1/2" OD x .040 with the bars contributing about 35% to a 1.35 deg/G roll gradient. That sounds more reasonable to me, but I'd appreciate any insight.

Thanks!

Marc Jaxa-Rozen
École Polytechnique de Montréal

[Cement Legs]

Hey http://fsae.com/groupee_common/emoticons/icon_mad.gif Joe, I feel a little silly for saying so, but I'm having a little trouble picking out the anti roll bar in the picture you posted. Nice front end though http://fsae.com/groupee_common/emoticons/icon_wink.gif. Is it the extra set of tubes comming off of your rockers?

[Didier Beaudoin]

<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>Originally posted by Cement Legs:
Hey http://fsae.com/groupee_common/emoticons/icon_mad.gif Joe, I feel a little silly for saying so, but I'm having a little trouble picking out the anti roll bar in the picture you posted. Nice front end though http://fsae.com/groupee_common/emoticons/icon_wink.gif. Is it the extra set of tubes comming off of your rockers? <HR></BLOCKQUOTE>

The anti-roll bar is a U-type one. It's the horizontal blue bar just forward of the steering rack. The tubes coming from the rockers actuate the ARB by pushing on both end of the U-bar.

[Cement Legs]

http://fsae.com/groupee_common/emoticons/icon_wink.gif gotcha... but im still having a little bit of trouble seeing the connection between the two, the frame bar is kinda blocking the view but i think im kinda getting the picture.

Denny if you read this post, I was looking at the solidworks picture of your team's front end and if im correct when the outside wheel goes through jounce the roll bar transmits a certain amount of force to compress the spring/damper on the inside? Is this roll bar calculated to have a certain k value? If so how do you calculate the amount of force you need to transmit. I understand everyone is busy right now so if time doesnt permit a detailed answer a nudge in the right direction would be appreciated.

[Denny Trimble]

CL,
Yes, any system with an anti roll bar will couple left and right single wheel bump to some extent.

We designed the system to meet our desired ride rates in bump (and natural frequencies), and our desired roll gradient (degrees per lateral G).

The springs are chosen first to satisfy ride rate, then the ARB is cranked-up until the springs + ARB gives the desired roll gradient.

If you're that concerned about one-wheel-bump, consider implementing a "distributed" anti-roll and/or anti-pitch system. I believe that's what UWA did this year, and I've heard of rally teams doing it as well.

If you can use hydraulic cylinders and lines to connect front and rear swaybar links on one side of the car, you can lessen the effect of your ARB stiffness in one-wheel-bump impacts. You can also do all kinds of crazy stuff... but I haven't spent much time working that out yet http://fsae.com/groupee_common/emoticons/icon_smile.gif

[Angry Joe]

Here's another method we never got a chance to implement...
http://www.we-todd-did-racing.com/wetoddimage.wtdr?i=wMjE0MjA2czQxM2RmZDMxeTU0MQ%3D% 3D

[Cement Legs]

HAHAHAHAH ROTFLMAO!!!! sweet... hmmmm no patent on that yet.... I just might steal it for myself whoaa hahahahha http://fsae.com/groupee_common/emoticons/icon_wink.gif