Steering Rack design

[Alastair Clarke]

Hi,

I'm looking for some advice. For a variety of reasons, we've decided to make our own steering rack. I'm planning to base it on commercially available rack and pinion, suitably modified, with a machined housing etc.

Have any teams done this previously, and can anyone offer and advice or forewarning of the pitfalls which await us?

Cheers

[Alastair Clarke]

Hi,

I'm looking for some advice. For a variety of reasons, we've decided to make our own steering rack. I'm planning to base it on commercially available rack and pinion, suitably modified, with a machined housing etc.

Have any teams done this previously, and can anyone offer and advice or forewarning of the pitfalls which await us?

Cheers

[jack]

make sure you can change the bushings, and pretty much take it all apart. on our last rack, one of the bushings needed to be replaced, but the clevises where perminent, so we were SOL. also make sure you can shim your pinion, to mesh it just right with the rack. its very difficult to nail this distance in fabrication.

mabye if james gets done playing death-ball, he can post a pic or two. http://fsae.com/groupee_common/emoticons/icon_wink.gif

[Big D]

We made one too. It is CNC'd in two halves, bolted together around the perimeter. These bolts are also what holds it to the chassis, and it adds strength to the chassis that way. One way of doing what Jack suggests is to make the bushings (teflon/plastic, in our case, split like an engine bearing, so they come apart with the case. The only thing ours is missing is the gear mesh adjustment. It works great now, but that will become an issue as it wears. The new car will probably implement the adjustment.

[James Waltman]

Jack asked for some pictures.
(For the record: deathball is stupid. It's the notpron puzzle that I'm addicted to.)

The rack was pretty much 100% Travis from design to manufacture.
http://dot.etec.wwu.edu/fsae/images/Steering%20rack%20center%20before%20assembly_JPG.j pg
http://dot.etec.wwu.edu/fsae/v35/bonding/images/Steering%20gear%20bonded%20into%20housing_JPG.jpg
http://dot.etec.wwu.edu/fsae/v35/bonding/images/Steering%20tie%20rod%20bonded%20to%20rack%20gear_J PG.jpg
http://dot.etec.wwu.edu/fsae/images/Steering%20rack%20cut%20away%20view_JPG.jpg
http://dot.etec.wwu.edu/fsae/v35/bonding/images/Steering%20rack%20mount%20bonded%20on_JPG.jpg
http://dot.etec.wwu.edu/fsae/v35/bonding/images/Fitting%20steering%20rack%20before%20bonding%20bra ckets_JPG.jpg

More of the same (but bigger) here. (http://dot.etec.wwu.edu/fsae/HostedPics/V35_Steering/)

Dan,
Are you willing to share some pictures?

[Evan]

We purchase our steering rack from a UK based company called Titan, that you are all likely familiar with (sold through Pegasus in North America) for 500 bucks retail. For another 100 bucks they will custom manufacture you one with any lengths you need. I too considered making one, but once we looked at the cost of materials combined with the amount of cnc machining needed to make a single housing rack that would perform like Titan's, and add to that the fact that they use a helical gearset and have an eccentric pinion housing and bronze slide adjuster for taking up lash, it was an easy choice. Any team could make a rack like this, but we decided that the cost difference (about 200 bucks we figure) between purchasing and making was offset by these extra features, and also it allowed us to focus on other areas of the car. We used to use Stilleto racks, which seem to be popular, but found that we needed a new one every year becuase of wear (in the past we had very limited funding and needed to reuse many parts). Finally, it is a bit heavy when you first get it, but a lot of weight can be lost by gun-drilling the rack itself, which is steel, or replacing it with Aluminium.

-Evan Martin
Ryerson University

[groessi]

Hi,

we are designing our own steering gear as well. We found a company who will manufacture us a steering rack and a pinion. Now that i saw the pictures i got two questions, maybe you can help: First what type of gearing has the pinion or what diameter is it? Because we wanted to work with module3 and have a diameter of 26mm, so that there will be only 9teeth on the pinion!!!( transversal gearing ). You got so manyhttp://fsae.com/groupee_common/emoticons/icon_wink.gif Second is how did you fix the pinion on the axle, did you weld it? And aren´t there problems of distortion? Hope you can help me, and please forgive me my bad english!!! http://fsae.com/groupee_common/emoticons/icon_smile.gif

[Chris Clarke]

If you are going to be building your own rack, unless you have the facilities at your university to do the gear cutting, try to get a stock gear set.

Our sponsors who did our gear cutting for us in the past originally told us that they would be able to give us our usual sponsorship on the gear cutting, so we designed our housing and gear set around this. Now they are saying that they are unable to provide us sponsorship for this season, so it is going to cost us upwards of $1500-2000 CAD to get it machined and cut. If we had gone with a stock gear set from the beginning, this wouldnt be a problem. Seeing as our housing is cast, we are limited in the amount that we can change this design also now, so we may be unable to find a suitable stock gear set that will work for our housing.

Chris

University of British Columbia
www.FormulaUBC.com (http://www.FormulaUBC.com)

[Frank]

lots of cad

buy a gear

http://www.gudel.com/en/products/components/racks_gears/spur_gears/index.php

i used 1.5 module for 100mm long steering arms

long steering arms = chunky pinion gear and rack, but gives more stiffness, and less tolerance required

buy metric ground bar (14mm or 16mm) for the rack, get the teeth cut

buy metric, pre-machined, Teflon impregnated bushes,

hydraulic wiper seals are good

machine some 2000 series ally for the housing

let the clevis but against the rack housing, for limits

machine small spacers to put between clevis and housing to centralize the rack for alignment

steering shafts 5/8"� OD 2.5- 3.0mm NWT 4340 no HT necc

use 5/8 apex uni joints

cross bolt or 6mm pins

hollow out every shaft as much as you can

deep groove bearings above and below the pinion, and a circlip to retain the pinion gear and shaft

the bearing above the gear will be heavy (˜cos it has to be bigger than the pinion gear), use the thinnest bearing you can get

[groessi]

Hi Frank,

thanks for all the information. For the mesh problem between rack and pinion i plan to machine a eccentric bush so that by turning it you can adjust the distance between both. ( copied it of (by?) titan-motorsport ) What seems to be a huge difference is the cogging! i mean you also have a diameter of ~ 32mm?! We seem to be overdesigning our cogging extremely. We thought that like 50Nm for the strain of the cogging is realistic???
So you already tested this in your car and there are no problems like teeth fracture or stuff? then i have to downsize our cogging, cos so we´ll need a diameter of 30mm for the rack!

[Frank]

uhhh

pinion diameter, i never said what it was

but what i can say is 130 degrees of steering at the wheel

28 deg at the inner wheel, 38 deg at the outer wheel (about 100% ackerman at full lock)

[rjwoods77]

Hey Evan,

How much did that titan rack weight when you were all done screwing with it? What wa you center to center distance for that weight?