what teams custom make steering racks?

[Dr Tron]

Last year (2011) I was in charge of steering for my team and went the way of custom making our our steering rack, I was just wondering what other teams have done the same? The rack worked great and we were able to lose about 3.5-4 lbs, the only issue is i need to work in a system for adjustable lashing. Rack in question pictured below
http://i20.photobucket.com/albums/b216/kylen20/IMAG0039.jpg

[Dr Tron]

Last year (2011) I was in charge of steering for my team and went the way of custom making our our steering rack, I was just wondering what other teams have done the same? The rack worked great and we were able to lose about 3.5-4 lbs, the only issue is i need to work in a system for adjustable lashing. Rack in question pictured below
http://i20.photobucket.com/albums/b216/kylen20/IMAG0039.jpg

[RobbyObby]

That's actually not bad from some that I've seen. Off the top of my head, GFR, UW-Madison, and I think ETS (correct me if I'm wrong) all ran custom steering racks last year.
There was also a team at West (MIT seems to sound familiar) that ran a cable/pulley actuated steering rack, their version of steer-by-wire I guess (or would it be steer-by-cable?).

[Some Guy]

When I was at Lime Rock RPI had one, pretty sure Brown and Cornell did to.

[Dr Tron]

i was happy with the result, its not as "clean" looking as i would like but that is due to all parts being made on the mill/lathe rather then CNC. Also it has a few degrees of play that developed after breakin period that i plan to fix.

The evolution of design will find the next rack with adjustable lashing as well as further weight savings throughout the rack.

im also looking for a better way to attach the input shaft to prevent any unneeded slop in the system. currently im using a slip shaft with through bolts... not a fan

[Adambomb]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Kyle "steering and suspension":
im also looking for a better way to attach the input shaft to prevent any unneeded slop in the system. currently im using a slip shaft with through bolts... not a fan </div></BLOCKQUOTE>

Check out taper pins, you can get them at Aircraft Spruce. You ream the hole out to a specific taper (they sell the reams too), and then the pin drops in and just "sticks" in place much like a press-in stud (fastener is plain on the fat end). The tolerance is self-tightening when you tighten down the locknut on the other side, and the whole deal installs quite cleanly and easily.

The design does look quite simple and effective. More do-able and functional looking than a lot of the student-designed racks out there. I'm imagining something involving eccentrics for lash adjustment might work? (I've got this thing for eccentrics lately http://fsae.com/groupee_common/emoticons/icon_biggrin.gif )

[Fyhr]

Lund Univ. have done several steering racks as well, most of them iterations based on a design developed for our second car.

Here is an example of linkage and rack from the third car, which added adjustability of the pinion to rack clearance.

http://i.imgur.com/xMPHHl.jpg (http://imgur.com/xMPHH)
The biggest issue is adjustment of the top beveled gear, where the majority of the play is exhibited. For our fifth car the rack and pinion part is relatively similar but the bevel gear has been replaced, I'll try to snap some pictures when i come by the shop.

Edit: Here is an earlier iteration out-of-car
http://i.imgur.com/pw61Gl.jpg (http://imgur.com/pw61G)
and installed-ish
http://i.imgur.com/kUfj3l.jpg (http://imgur.com/kUfj3)
Inside the bevel gear:
<a href="http://www.luracing.se/index.php?page=browse&album=LUR4/Manufacturing_2010/" target="_blank">
http://www.luracing.se/album/LUR4/Manufacturing_2010/1271867761luracing_tillverkning-51.jpg </a>

[Dr Tron]

i have seen other teams use a similar system, do you find this gives you less play than a simple intermediate shaft with universal joints of some kind? how do you adjust your clearance between rack and pinion?

[Dr Tron]

another question for those making racks is what type of gearset you use? i found machining a set of my own beyond my abilities (not to mention al would be too soft unless heat treated) so i ordered a set and fixed it to my "rack"

here is a photo in-car
http://i20.photobucket.com/albums/b216/kylen20/IMAG0075.jpg

[Rex Chan]

We buy the rack/pinion from an industrial gear place in Queensland, AUS. The housing is fabbed alum 9by sponsor Rob Black Engineering). The moving, internal bits are machined by the uni workshop.

Here's a video of it in the 2011 car. The original housing design was from way before I started (I think it was a 2005 design), containing a Bishop Engineering rack. In 2010, we got a replica housing made and replaced the gearset with the one from queensland. This year (2011), we moved to a bigger pinion, and got another housing made up - Melbourne Uni FSAE 2011: Steering Rack Partial (http://www.youtube.com/watch?v=Y6lTV2Jp2d0)

Melbourne Uni FSAE 2011: Steering system fully assembled (http://www.youtube.com/watch?v=EbWcgQgeT5I)

Compared to the one's above, ours seems to use a lot less machined parts, which is faster/easier for us.

[Fyhr]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Fyhr:
[QUOTE]Originally posted by Kyle "steering and suspension":
i have seen other teams use a similar system, do you find this gives you less play than a simple intermediate shaft with universal joints of some kind? how do you adjust your clearance between rack and pinion? </div></BLOCKQUOTE>

The first revision used flat solid shims between the pinion bearing lids, the second revision used hard rubber shims to allow higher tightening running with higher interference while retaining some elasticity to avoid lockup (if i recall correctly).

The bevel gear does not give less play than any other solution, in our case it was a large source of play, especially after running for a few competitions. I believe the reason it performs poorly is the bevel gears only being held by a keyed joint, with no possibility to shim the gears together. In a recent discussion with a transmissions professor he suggested using belville washers for shimming the gears together, yet again allowing high interference without lockup, this would however increase friction in a steering system that is already fairly grave.

The reason we used this solution is packaging, on these cars we've run 10" wheels with 7 deg caster, there was simply no room for the steering arm low-front on the upright.

On the most recent car, the team have moved away from the 90deg gear and run low-front
steering in 13" wheels, here is the rack.

http://i.imgur.com/xriCKl.jpg (http://imgur.com/xriCK)

We also purchase our gear components, again if i recall correctly, we've used modulus 1.5.

[Dr Tron]

looks great, any issues with those gears being exposed?

[Fyhr]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Kyle "steering and suspension":
looks great, any issues with those gears being exposed? </div></BLOCKQUOTE>

Lack of lubrication, this car isn't finished. I think there's supposed to be a cover plate over the gear.

We've never covered outer gears on the rack though, i guess we couldn't find a small enough rubber cover, so we just run a thick moly-grease.

[buggaero]

We'd installed a custom rack and steering , in 1.5 module and it saved us around 4-5 pounds than our previous car.
The only problem in the design was , it being not easily disengage-able. It wasn't CNC'd but the lathe guy just buffed it to mirror finish. So can't say it wasn't neat.There surely some play, although minimal, in the end bushes of the rack after the event.


Mechsonic Racing.
New Delhi.

[Dr Tron]

yes this one saved us a significant amount of weight as well and the amount of play is not significantly worse then previous bought racks however I would like it to be better and just recently locked down a design for adjustable lashing on the next rack.

I machined every part of this rack aside from the carbon fiber housing (bought and then machined to fit) and it was a real learning experience as it was my first time getting some experience in the machine shop. I learned alot obout being paicent and doing things right the first time as well as having a plan before entering the shop. as you can see it is a pretty sturdy unit right now and with some careful planing and intelligent design alot of weight can be saved, right now im excited to get into the shop and put my plans into action... sadly i need to make revisions to the cad model first http://fsae.com/groupee_common/emoticons/icon_frown.gif

http://i20.photobucket.com/albums/b216/kylen20/FSAE/IMAG0038.jpg

[Dr Tron]

note those clevisis were not used, just a rough draft so to speak

[Fyhr]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Kyle "steering and suspension":
note those clevisis were not used, just a rough draft so to speak </div></BLOCKQUOTE>

Do you use the cogged rack all the way or is it attached to some hollow profiles for the bit out to the clevises?

One quick (but minor) weight reduction you could perform is to get a 45 deg end mill and just add a chamfer to the pinion housing.

All in all it looks really neat, the clevises are very similar to the ones we've used, the only difference being the slots for the rod-end mount were milled with a round end mill.

[Dr Tron]

it is not cogged all the way however the rack set is attached to one solid piece of aluminum whos diameter steps down beyond the section the rack is attached to. next-gen will have hollow attached sections which you might thing would be difficult based on the pinion providing a force on the center and it being supported only on the outside however if you look at on of the installed in-car pics (i will repost as they are not able to be viewed because i moved some things around) you can see a bolt going through the bottom of the pinion housing; this holds in place a section of bearing grade bronze (same material used on both the endcaps as well as the pinion gear plates) machined and polished with a chamfered flat spot the rests against a flat spot machined into the "rack" both helping prevent a large bending momment as well as help in preventing rotation of the reck in relation to the pinion gear.

http://i20.photobucket.com/albums/b216/kylen20/FSAE/IMAG0039.jpg

here (below) you can see the bottom bolt

http://i20.photobucket.com/albums/b216/kylen20/FSAE/IMAG0075.jpg

exploded view (giving away my secrets) but pretty early in production (aka still plenty of secrets) also the tape was on for cutting and fitting simulation of epoxy

http://i20.photobucket.com/albums/b216/kylen20/FSAE/IMAG0037.jpg

[BMH]

^^ Very Nice! Do you have any numbers in terms of weight and steering ratio?

[Dr Tron]

3.4 lbs vs 7 and 9 respectivly for our previous bought racks, Rack ratio is about 3.14:1 depending on lashing and i would have to double check some math on suspension geometry to get an overall SR

[DReddy]

Hi,
These might be silly questions but we have just started the design of our car and i was looking at some steering designs. The vertical steering column looks ideal to reduce the rack length, but I have a few concerns.
1.wont a vertical steering column be an obstruction to the template that has to be passed through the cockpit.
2.I understand that there is an exception for steering column given in the rule book, but the template still wont get through. So, should be designed such that it can be removed during design scrutiny.
3. Would an additional bevel gear add to the steering effort, also floor mounted rack might create a high angle between the rack end and tie rod end.

[Z]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by DReddy:
... we have just started the design of our car and i was looking at some steering designs... </div></BLOCKQUOTE>
And as your goal, I guess you want a lightweight, stiff, low friction, backlash free steering linkage, going from the steering wheel out to the front wheels.

So if I may suggest...

Firstly, forget about copying the "standard" arrangement, and then trying to polish it. You can come back to that as the "last resort".

But if you want to do it "better", try to think of the problem from first principles.

So, thinking ... hmmm ... want minimum path from hand wheel to front wheels ... hmmm ... linkage with right ratios ... hmmm ... less is more ... hmmm ... etc.

So take a look at Pontus Fyhr's bevel gearbox pictures at the top of page 1. Hmmm...

How about ...
if you make that a 3:1 ratio ...
and then put a bellcrank/pitman arm at the bottom of the vertical shaft???
And then the steer-arms go outward, and a little forward, from the pitman arm to the wheels ...
A simple linkage following a pretty direct path???

Furthermore, you mount the vertical shaft in needle roller bearings (or perhaps bronze bushes for the first draft), and let it slide vertically. Now with the larger "crown" bevel gear sitting on top of the smaller pinion bevel (3:1 remember), you can apply slight downward spring pressure to the crown to eliminate all backlash! And friction is less because all "roller bearings" (or low speed rubbing) rather than the higher speed rubbing (and rattling) of the rack.

And ... you might even be able to use the crown and pinion bevels from a small differential (ATV)? (You need less than half of the crown wheel.)

But, for complete lack of bump steer the bottom wishbones will have to mount close to the centreline of the chassis. Hmmm. But with the minimal wheel travel, only +/-1", a small mismatch in steer-arm/wishbone length will be immeasurable. Hmmm ... better measure it...

Now to figure out the Ackermann geometry ... (hmmm ... looks good! http://fsae.com/groupee_common/emoticons/icon_wink.gif).

Hmmmmmm ...

Z

[Drew Price]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Z:

How about ...
if you make that a 3:1 ratio ...
and then put a bellcrank/pitman arm at the bottom of the vertical shaft??? </div></BLOCKQUOTE>



Danger nonlinearity, danger!

[Kevin Hayward]

Z,

UWA have run a very similar setup for the past few years. Works well for them. Another advantage is different designs for Ackermann etc are very easy on the lower arm.

Kev

[Z]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Kevin Hayward:
UWA have run a very similar setup for the past few years. </div></BLOCKQUOTE>
Kev, thanks for that. Sometimes it's nice to get confirmation that I'm not completely nuts. http://fsae.com/groupee_common/emoticons/icon_smile.gif

(DReddy, if you ask nicely, someone at UWA might post some pics...)

Z

[Z]

I'll have a further rant on this while it's in my head.

I see the R&P + Bevel-Gear-Box as an example of "creeping complication". The designer figures he has to have the R&P "because we've always had it", but then packaging issues force the addition of the extra BGB ("selfish driver won't have his legs shortened!").

For some reason many designers don't see that the addition of the second part (BGB) means that the original part (R&P) can be dropped. (And this is not meant only as a criticism of FSAE, because it also happens in many other fields.)

Anyway, if I were the hypothetical purchaser of an FSAE car, I know that when I saw the R&P and BGB I would get that sinking feeling in my stomach, and think "Why, why, why, why, why?????

1. Why do I have to pay for BOTH a R&P, AND a BGB?

2. Why will I have to spend countless hours shimming both of those to get the backlash out?

3. Why, even after all the shimming, will the steering be loose at straight ahead, and then bind up with far too much friction at half-lock?

4. Why couldn't they just build something simple, cheap, easy-to-maintain, reliable, and that just works well?

5. Why always the unnecessary complications?????

(Again, not directed only at FSAE, but modern product design in general. http://fsae.com/groupee_common/emoticons/icon_smile.gif)

Z

[Pete Marsh]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content"> (DReddy, if you ask nicely, someone at UWA might post some pics...)
</div></BLOCKQUOTE>
No problem, but not 2 weeks before comp. Kind of stressing right now.

Heaps of people took pics at FSG 2009, so maybe someone else can post one, and it's still similar except for the addition of a nice sand cast housing for the gear box and steering wheel reach adjustment.

Pete

[Thrainer]

Do you mean the steering system featured in the ATZ FSG special? Must have been in 2008 or 2009.

[BenjaminL]

Ben Gurion Racing Team Also ran a Custom made Steering rack.

Rack And Pinion - 4030 Steel.
Housing - Magnesium.
CV Joints - 2 Apex HD CVJ

http://www.facebook.com/photo....&type=1&ref=nf[/IMG] (http://www.facebook.com/photo.php?fbid=10150330592478126&set=o.321108885444&type=1&ref=nf%5B/IMG%5D)

[Dr Tron]

"Costume" ehh... sexy pirate or sexy police woman?