Is this a good design?

[Horace]

I just saw this while browsing Washington's gallery of FSAE photos of other cars.

http://www.fsae.me.washington.edu/fsaewest2007/othercars/pages/IMG_0586.html

I don't know whose it is, but I've seen many similar designs of how the spherical bearings are attached to the upright like it is in this photo. My question is if its good to design the placement of the spherical bearing laterally away from the main structure of the upright, if the spherical bearing holds the A Arm that is also attached to the push/pull rod. I've seen this proven design very often in the less loaded ball joint, but not so much on the loaded one.

[Horace]

I just saw this while browsing Washington's gallery of FSAE photos of other cars.

http://www.fsae.me.washington.edu/fsaewest2007/othercars/pages/IMG_0586.html

I don't know whose it is, but I've seen many similar designs of how the spherical bearings are attached to the upright like it is in this photo. My question is if its good to design the placement of the spherical bearing laterally away from the main structure of the upright, if the spherical bearing holds the A Arm that is also attached to the push/pull rod. I've seen this proven design very often in the less loaded ball joint, but not so much on the loaded one.

[Ecks]

That does seem like it could be an issue. No doubt, there is a bending moment present. On the somewhat tolerable plus side, it appears that an attempt was made to keep the projected axis of the pushrod more or less going through the mount on the upright.

[screwdriver]

It's an inverse rod-end-in-a-bending.
They've sucessfully evaded the rod-end in a bending when it comes to vertical loads by attaching the push/pull rod at the bottom, but under braking it's in a bending again.

It's a strong rod end though, so probably won't break. But that's just a guess. Only the exact calculations will reveal what it's got to hold.

But to conclude: Is it a good design? - No, I don't think so.

[murpia]

I don't see any rod ends in bending...

Staking sphericals into a bracket, then mounting that bracket with studs / bolts and adjustable width shims to the upright is quite a common practice to allow adjustments to be made.

However, as executed here there are a number of drawbacks, so I wouldn't copy it:

1) The bottom balljoint housing takes vertical & braking loads as cantilever. Could flex too much and / or weigh too much.
2) The camber shims appear to be on the lower spherical bracket, adjusting those shims will throw the toe adjustment off.
3) Combine items 1) and 2) and your stiffness takes yet another dive...

Better to mount the lower spherical direct to the upright, then stake the top spherical only into a housing that's shim adjustable for camber.

Regards, Ian

[PatClarke]

Hi all,
Anyone want to comment on the amount of scrub radius here?
Anyone want to comment on the hub flange where the wheel bolts?

As Ian points out, if the camber shims were behind the top spherical bracket rather than the bottom one, then a camber adjustment would have minimal or no effect on toe. This alone shows the judges that the designer hasn't thought the whole thing through.

It's an acceptable, though not good, solution.

Cheers
Pat

[John Grego]

That is our '07 car. We like this design a lot and have had no problems with reliability.

[BamaJeff]

It was good enough to win...so you can't really argue with that.

[Steve O]

If the forces were calculated out and it has a reasonable factor of safety, what would be the problem with that design? Camber adjustment will always effect toe and as long as your tie rods are designed properly you can adjust the length to negate that. Also placing camber shims on the top would have reversed their camber adjustments so that post doesn't make a whole lot of sense to me although I could be missing what you are saying(not trying to bash, I just don't follow your logic). I'm also not seeing the rod ends in bending... there is a bending moment on the a-arm from the push rod, but no rod ends in bending. The upright connections are probably using shear bolts and the push rod shouldn't see much of your accel/ decel as that is supposed to be handled by your a-arm.

I think murphia said it best when he said it's a common practice with pros and cons like any other design.

Steve

[murpia]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Steve O:
If the forces were calculated out and it has a reasonable factor of safety, what would be the problem with that design? </div></BLOCKQUOTE>
Low specific stiffness subject to vertical loads.

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Steve O:
Camber adjustment will always effect toe </div></BLOCKQUOTE>
No, if (for example) the toe link and lower balljoint are mounted on the same bracket, and that bracket is shimmed to the upright, toe will never change with camber. This is common practice on many racecars.

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Steve O:
Also placing camber shims on the top would have reversed their camber adjustments so that post doesn't make a whole lot of sense to me although I could be missing what you are saying(not trying to bash, I just don't follow your logic). </div></BLOCKQUOTE>
Yes, putting camber shims at the top not the bottom reverses the effect of adding / removing the shims, but that's not going to be very difficult to handle... Or did you mean that the 'no shim' case would be 0deg camber and therefore the physical impossibility of negative shims is a problem? I don't think we can answer that from the photo, but all you need is the relative geometry of the brackets to be designed right and off you go...

Regards, Ian

[Steve O]

Ian, I agree with all the points you made; however, your second point about toe changing, I should have been more clear as I was referring specifically to the picture above with the toe link not attached to the shimmed bracket, but point well taken about vertical load stiffness.

Also, to answer your question in your 3rd point, it was a retort to the post about putting the shims under the top bracket instead of the bottom bracket. The reason I don't think this is a valid argument to say that this assembly was done poorly is because both brackets are there for a reason, you may need to shim in either direction. Of course if your relative geometry works out perfectly then yeah you would only need to shim the intended side but shimming either side with their setup doesn't make a difference either way except in the direction their camber changes because of the point above about the toe link not being part of the shimmed assembly.

Hope that clears things up.

Steve