Control Arm Shims

[TheGreatBenny]

What are some methods to use shims to adjust the suspension geometry. We have decided to avoid using threaded rod ends, which means we cannot simply weld tabs on the chassis. Having a difficult time coming up with ideas to incorporate a removable bracket on the chassis for the control arms.

[whiltebeitel]

You could make a bracket with 2 holes that bolts to the chassis. Weld/bond 2 threaded chassis inserts. Then, design some shims out of flat stock that can drop right in between the bracket and the chassis. It's really not that novel of an idea.

[RobbyObby]

Originally posted by TheGreatBenny:
We have decided to avoid using threaded rod ends, which means we cannot simply weld tabs on the chassis.

Who says you can't? As long as your manufacturing tolerances are spot on, there's no reason you should ever really have to use rod ends. However, if you aren't precise you can introduce unwanted bending loads in the control arms.
Are you trying to add these special brackets simply because you don't think you can weld on a bracket, or are you actually trying to make adjustable kinematics? I've seen brackets done with large spacers to move the inboard points up or down to adjust roll center heights and anti- geometries, but that's it. What are you trying to actually accomplish?

[OspreysGoSWOOP]

Who says you can't?


Pat Clarke.

He makes a pretty strong argument against it here.

http://www.formulastudent.de/d...rod-ends-in-bending/ (http://www.formulastudent.de/de/academy/pats-corner/advice-details/article/pats-column-rod-ends-in-bending/)

Our car is using a system exactly like whiltebeitel suggested.

If you want I can send you pics/drawings etc

[Dash]

Pat doesn't say you can't either, just suggests that it probably isn't the best idea. :P


Originally posted by OspreysGoSWOOP:
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Who says you can't?


Pat Clarke.

He makes a pretty strong argument against it here.

http://www.formulastudent.de/d...rod-ends-in-bending/ (http://www.formulastudent.de/de/academy/pats-corner/advice-details/article/pats-column-rod-ends-in-bending/)

Our car is using a system exactly like whiltebeitel suggested.

If you want I can send you pics/drawings etc </div></BLOCKQUOTE>

[Big Mo]

It's all cost/benefit. In board rod ends aren't the best structural solution (they are a close second to fully-encapsulated), but they do offer the benefit of allowing more loose tolerances and take less time as well...Essentially, they are the most practical.

On the other hand, using adjustable brackets can introduce compliance. I believe I saw an article by Pat on that, as well...

http://www.formulastudent.de/d...ness-and-compliance/ (http://www.formulastudent.de/de/academy/pats-corner/advice-details/article/chassis-stiffness-and-compliance/)

[Adambomb]

I'd go so far as to say it's all in the details. I would say that it is certainly possible to design adjustable brackets that don't introduce any more compliance than simple tabs. I would also say that even on Pat's page about REIB, there is certainly a combination of locations he lists himself (although perhaps not explicitly) where you could use rod-ends without introducing any bending; in fact, if you take into account a-arm warpage when welding in spherical bearing retainers, you could even use rod-ends to REDUCE bending loads in a-arms. There is also certainly a case where you could justify them from a manufacturability standpoint, if nothing else just due to the fact that threaded inserts are much easier to make than spherical bearing inserts.

[PatClarke]

Wow,

People actually read that stuff http://fsae.com/groupee_common/emoticons/icon_smile.gif http://fsae.com/groupee_common/emoticons/icon_wink.gif

Pat

[Jan_Dressler]

Originally posted by PatClarke:
Wow,

People actually read that stuff http://fsae.com/groupee_common/emoticons/icon_smile.gif http://fsae.com/groupee_common/emoticons/icon_wink.gif

Pat
"That stuff" is actually a "set book" for everybody in our team, and I believe that goes for a lot of other teams as well. Thank you a lot for that! http://fsae.com/groupee_common/emoticons/icon_smile.gif

And, by the way, one of "that stuff" helped me to convince my team bosses to go the dry sump route back in 2007/2008, which meant that I was allowed to do our first such system. It has, in all its iterations, never failed till today http://fsae.com/groupee_common/emoticons/icon_smile.gif
Thanks again.

EDIT: Typo...

[PatClarke]

Thanks Jan http://fsae.com/groupee_common/emoticons/icon_smile.gif

I'd better write some more then! http://fsae.com/groupee_common/emoticons/icon_wink.gif

Pat

[Jan_Dressler]

Do it! Faster! http://fsae.com/groupee_common/emoticons/icon_biggrin.gif

Man, I miss my FSAE days (or years). They certainly made me a better engineer. And "that stuff" was always a huge part of that.