Rack and pinion Steering

[Manuel P.]

http://fsae.com/groupee_common/emoticons/icon_cool.gif what r the advantages in making your own rack and pinion over buying it?

http://fsae.com/groupee_common/emoticons/icon_cool.gifdoes any1 knows what companies offers great prices/discounts for rack and pinions?

thanxs

[ben]

We are currently building our rack and pinion for the third year in a row.

Advantages are that you have total packaging freedom and can make it smaller than most commercial racks. We're doing a composite monocoque and have been able to integrate the mounting for the front shocks and the steering rack into the same inserts by having our own system.

Disadvantages are mainly machining time.

Ben

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

[Stephen Soroosh]

Ben,

Have you guys had any gear meshing problems? What kind of contact ratio do you use? Do you have a rack guide? We have been considering making our own rack but the fine details can be scary. Just wondering what your experience with it is.

~Steve

If man is not made for God, why is he happy only in God?

Blaisé Pascal (1623-62)

[Frank]

I consider the whole design a trade off between.

Stiffness in the steering mechanism: due to Ackerman and high steering angles, causing a small lever that the tie-rod acts about the kingpin.

VS

Weight of rack: from larger pinion gear required and the extra length to achieve the required travel.

For our new car I have set low camber gain in roll / high camber gain in bump, to help get the rack under the drivers legs.

The tie-rod bisects the planes of the upper and lower a-arms.

This increases stiffness.

I have used long steering arms so my total travel is 3.6" L-R and total steering angle 250 deg L-R

I used a 30 tooth 1.5 module pinion, ptfe sintered bushes, and hydraulic wiper seals
The housing was billet 2011.

I used metric ground bar and had the teeth cut, and bought a Gudel pinion.
Conveniently, the metric ground bar is about the correct undersize for the bushes.

I wouldn't use an aluminium on the contact surfaces of the rack and pinion, because you end up with similar weights when you upsize the module for the ally.

One idea is to graft steel teeth to aluminium bar to get a rack. But I think this a mission * 1.5

Mine is a BEAST at 3.2 lbs, you could make one well under 2 lbs, but I like my steering stiffness at 26deg L /38deg R.

One other point is that when you have a larger diameter pinion, you don't have to stress about the clearance causing slop.

Heres some links I like.

http://www.glyco.de/en/lieferprogramm/gleitlagerwerkstoff/index.htm
http://www.gudel.com/en/products/components/racks_gears/rack_pinion/index.php
http://www.uq.edu.au/fsae/2003%20Photos/Comp/Dsc01223.jpg
http://www.uq.edu.au/fsae/Frank/rack.jpg

[ben]

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

Have you guys had any gear meshing problems? What kind of contact ratio do you use? Do you have a rack guide? We have been considering making our own rack but the fine details can be scary. Just wondering what your experience with it is.

~Steve

If man is not made for God, why is he happy only in God?

Blaisé Pascal (1623-62)
<HR></BLOCKQUOTE>

No meshing problems to my knowledge. Don't know the contact ratio off the top of my head.

The housing is machined aluminium (bonded in three pieces this year to make the individual bits easier to machine). The rack is supported at the outboard end by recirculating ball linear bearings each 36mm long. We also have a backlash adjuster under the rack that has a PTFE block in it.

Ben

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

[Rcha]

Manuel,

although making your own is definitely worth it so that you get exactly what you want (weight, packaging), it has always been worth it for our team to get off-the-shelf if possible. We've used the Stilleto dragster Rack from Chassis shop for 3 years and love it, and it's only $260 with a 12:1 turning ratio. I believe UTA and UMC use the same rack, it's pretty popular. It comes with boots that protect the gear and pinion and we've NEVER had a problem with it, esp if you set it up right. Not too bad for a little rack. We machine extensions with clevis' to our tie rods. Works great. Check it out:

http://me.unm.edu/~fsae/teams/2004/car/recent/feb_12_06.JPG


It depends on how much time you want to spend making your own. If you have the time, go for it. If not, buy one and move on with the rest of your car.

[Denny Trimble]

Rcha,
What bushing material do you use for the outer supports?

University of Washington Formula SAE ('98, '99, '03, '04)

[albrewe]

Denny,
We are just using a simple machined delrin insert that is press fit into the chassis.

http://me.unm.edu/~fsae/teams/2004/car/recent/2004_feb/feb_12_06.JPG

Andrew Brewer
Racing Lobos 2003-2004
University of New Mexico