Rack N Pinion Offset?

[Ryan Boysen]

Hey FSAE'ers

I know someone knows the answer to this..

We have a 10:1 Ratio RnP.. However.. we don't know what the optimal offset from the center of the upright should be. There has to be an equation.. or somthing. The Rack didn't come with any paper work, so we are lost. Any Ideas?

[drivetrainUW-Platt]

are you talking front to back offset, I belive what you are looking for is ackerman steering, if so do a search for it

[mm davari]

hi RB
if you are talking about the length of steering arm and the offset of steering ball joint connection from wheel center and up right there is really good approach in milliken"chassis design"

[Belo]

I know there are good topics on that in certain books, a good thing is to simulate your steering in your cad software... this way you can do the final tuning to obtain the desired ackermann

(is that for this year car???)

[Ryan Boysen]

Belo..

Honestly, Yes. We are a first year team, trying to get it done. Getting close, just a few other things to finish up, i.e. steering. We made the uprights so we could weld on the steering tie rod attachment.

A rough ballpark from someone would be greatly appreciated.

[Mike Cook]

Because i'm feeling generous:

Ours is about 2.5 inchs in front of the top ball joint. You want to run probably as much ackerman as you can which means you want the point further out than your ball joint. I can't remember our steering rack ratio so your numbers will vary. It is very easily to geometrically calculate this stuff. for instance, determine how much steering wheel motion you want (~180degrees) calculate how much movement that gives your tie rod, then calculate how much you want your wheels to turn (~30 degrees each way) and then determine your offset.

[Dan B]

This is a spreadsheet that RaceTech had up on their website back in '99.

http://mysite.verizon.net/triaged/files/ackermann.zip