Camber adjustment?

[Steve-Imperial]

Basicaly ive narrowed down the methods of front camber adjustment to two means:

- Having the lower wishbones finsh about 70mm before the upright, where a CNC machined aluminium part is bolted containing the upright spherical bearing. There's shims between the aluminium part and the wishbone end for adjustment. I think this may be a little complicated, expensive (on cost report) and weak...

- Having both upright spherical bearings built into the wshbones and leaving camber adjustment to be achieved with the adjustable wishbone ends at the chassis? Do the judges frown on this?

What are peoples opinions on this subject? Obviously the easiest way is to use a rod end in bending but thats what im desperately trying to avoid!

[Denny Trimble]

One advantage of the first method you describe (shims between the steering arm and the upright) is that you can independently adjust camber and toe. If you adjust the inner points, you will probably have to correct your toe every time you change camber, at least at the front. However this method does require a bit more design work to make it strong, light, and easy to manufacture, which you noted.

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

[madhay]

<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>Originally posted by Denny Trimble:
One advantage of the first method you describe (shims between the steering arm and the upright) is that you can independently adjust camber and toe. If you adjust the inner points, you will probably have to correct your toe every time you change camber, at least at the front. However this method does require a bit more design work to make it strong, light, and easy to manufacture, which you noted.

University of Washington Formula SAE ('98, '99, '03, '04)<HR></BLOCKQUOTE>

I don't quite see how either method can isolate toe from camber adjustment. I think Steve was talking about having shims between the spherical and the arm itsself, not between the steering arm and the upright (how would that change camber-unless the spherical attachment and steering arm are one piece but seperate from the upright?)

[Denny Trimble]

You're right, I didn't read his post that carefully. I thought he was describing the sensible way to do it http://fsae.com/groupee_common/emoticons/icon_smile.gif

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

[ben]

The only way to adjust camber in isolation from toe is to mount the track rod and one wishbone on a common outer bracket and shim between this bracket and the upright.

If you look at any F1 car, this is what they do. Chalmers had a very neat approach to this on their car.

Ben

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

[Angry Joe]

<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>Originally posted by madhay:
I don't quite see how either method can isolate toe from camber adjustment. I think Steve was talking about having shims between the spherical and the arm itsself, not between the steering arm and the upright (how would that change camber-unless the spherical attachment and steering arm are one piece but seperate from the upright?)<HR></BLOCKQUOTE>

That's how we do it on all our cars. It's not that difficult...

By the way, I would stop worrying about the judges are going to think. Worrying about whether the design is sound would be much more productive.



Lehigh Formula SAE Alumni
Team Captain 2002-2003

www.lehigh.edu/~insae/formula (http://www.lehigh.edu/~insae/formula)

[Steve-Imperial]

I was indeed talking about having shims between the spherical and the arm itslf. I saw this used on the Brunel car upper wishbones I think.

Unfortunately the idea of using a common bracket with the steer arm and lower wishbone is impossible with my design. Im using fabricated steel uprights with the woshbone mounts in single shear. The proximity of the wishbone sphericals to the brake disc prohibit the use of double shear bracket designs. However I am using a double shear bracket for the steer arm mount which being separate from the camber adjustment enables changine th acermann angle.....

"worrying about whether the design is sound would be more productive"
This is very true http://fsae.com/groupee_common/emoticons/icon_smile.gif

I think im likely to go back to my original simple design and use the inboard wishbone adjustments to change the camber

[Travis Garrison]

Steve,

...wouldn't what you are doint simulate a rod-end? ...in that your camber adjustment is going to be linked to kpi? which seems to be about as bad as the toe problem...or am I missing something here...

The shim method of adjustment is the biggest reason I see for getting away from rod ends and going to sphericals, you can over build rod ends to the point that they will last a very long time for a very minimal weight penalty...if your going to simulate the adjusment you'd get from a rod end I'd say save yourself the headache and simply use rod ends as they result in components that are much easier to manufacture.

Travis Garrison
WWU FSAE

[Frank]

I know turning inboard rod ends is a pain, but if you calculate all the geometry (use cad), and have a spreadsheet, you can get it right quite easily.

Our spreadsheet can give you the number of turns to change castor camber wheelbase and track simultaneously, and yes it does work.

You have to remember to re-adjust ride height after you do it.

As for toe, my preferred method is to have a cheap "pen laser" mounted to the chassis, which fixes a centreline. You then have lasers on little 90 blocks that rotate in hollow axles.

No strings necessary, all you need is a wall, and a tape measure.

[Steve-Imperial]

Changing the wishbone length will change the KPI but not by much, it will just be the same as whatever the camber angle is with my upright design (0.5-1.5 degrees)

Since we are having outboard pickups this time (our first cars internal pickups were an incredible pain in the ass!!) I think the inboard end adjustment will be utilised http://fsae.com/groupee_common/emoticons/icon_smile.gif

Cheers for advice Frank, incredibly useful!
One last query though: when you start making large changes with the inboard adjustments (like what would be needed to change wheelbase)doesnt it put bending loads on the wishbone arms and welds? I guess they're negligible in relation to the loads when running the car....

Your method of toe adjustment is very ingenious! It must rely very heavily on accurate mounting for the lasers though!

[MattG]

Chassis mounted alignment systems rely heavily on a chassis which is perfectly straight. It may not be a major concern in FSAE as the odds of bending a chassis a hopefully pretty small, but you're putting a lot of faith in those laser mounts (and everything else) being straight.

Every system has it's short comings though

[Frank]

the idea is to set it up once on a 4 wheel aligner

then set up the chassis reference laser

from then on use the chassis laser as a reference

its easy to get the wheel lasers pointing true, but difficult to explain

bending loads in wishbones.. yeah that happens indeed, and they get hard to install

its a great way for checking if you've got bump steer, turn lasers on and step on car!!

you can check camber by scribing lasers up a wall

as for "trusting the chassis reference".. you change one end of the car at a time, and check what you're doing

i think you'd be very unlucky to twist a chassis, unless the engine is stressing the chassis hard, and you then remove the engine

[This message was edited by Frank on February 15, 2004 at 05:17 PM.]

[markocosic]

Digging up an old thread again:

How do you true the wheel lasers?

Any of the German teams know where the nearest 4-wheel alignment centre/tyre fitting centre is to the Hockenheim ring? (or what "Kwik Fit" is in German... http://fsae.com/groupee_common/emoticons/icon_wink.gif )