Carbon Control Arm Joint Design

[mlane90]

First off, hello all - first time posting but I've been lurking and doing research for a little while. I'm spearheading my teams efforts at going to carbon tube+aluminum suspension structures for 2014 and I wanted to bounce some ideas off of you all. I've found tons of good info on bonding, epoxy, etc so I won't beat that dead horse any more, but right now I'm a bit more hung up on the problem of designing the aluminum joints.

I have several viable options going for the inboard points. There are three general schools of thought (in my mind) here:

1. Make a clevis type joint that inserts into the tube and somehow mount the bearing to the chassis. This option is easy to manufacture on the CA side, but I can't wrap my head around how we could make a bearing cup and stake a bearing on the chassis side. (we have a steel tube chassis, this would be easier to accomplish with a monocoque I think)
2. Make a custom rod end that inserts into the tube and has the bearing pressed into it, leaving traditional tabs as the only hardware needed on the chassis side. Massive work on the manufacturing end, however this would be the cleanest execution.
3. Make a bung that inserts into the tube and then tap it to receive a threaded rod end. This is by far the easiest solution to implement. However, it introduces extra components and linkages which is a definite con - the rod ends would most likely be the weakest link here.

At the outboard/upright end I'm more up in the air:

1. Elbow joint with two female holes to receive tubes
2. Elbow joint with two male plugs that insert into tubes, similar to inboard side. Can't even fathom how these would be manufactured without some machining wizardry that we don't have access to (in house, at the least).

I don't have much in the way of ideas as to how to get spherical bearings into the upright side either. Pic below for reference; they're using the custom rod end and female A-arm joint options from above, and the tie rod looks like it had the bung+threaded rod end design.

http://oi45.tinypic.com/2hmzsb8.jpg

Let me know if you have any experience, suggestions, improvements on my ideas, or if you need clarification on the above (I have CAD models of all five, just to lazy to put in screen-caps of them all). Thanks a ton!

- Mike

[Charles Kaneb]

With carbon control arms, you may as well hang for a sheep as a lamb. Use flattened carbon or ti flexure pivots - your carbon and adhesive work have to be good enough to do this even if you don't, because these are safety-critical parts.

[mech5496]

You will find that the hardest part to get right is the upright side. The easiest solution would be to fabricate those instead of machining. Lathe a ring for the spherical to be pressed into, then weld short sections of steel tubing to it (as you would do with steel AArms but much shorter) and add pull/pushrod pickups (2mm sheetmetal?) Prep the short tupes and bond them to your CF tubes... http://fsae.com/groupee_common/emoticons/icon_wink.gif

[Goost]

One combination not mentioned; if you were to use rod ends with threaded inserts inboard and nested clevises outboard you get two advantages:
1) The location of the upper ball joint can be moved ~.5" longitudinally or laterally to adjust the kingpin axis (caster and KPI adjustment)
2) The links are very much more a '2 force member', ie no bending loads due to improper manufacturing or measurement. The carbon arms (which are mostly uni-directional or perhaps pultruded fibers) I would not expect to be much good in any bending condition: the resin alone provides the shear reaction in a uni/pultruded tube in bending.

[onemaniac]

If you're going to howl the car inside a trailer to competitions, whatever glue you use, make sure it can survive high temperature. I've seen a bad thing happening...

[Goost]

Here is a picture of our setup for reference. This is obviously the rear, and being adjustable is more useful for the front, but the upper arms I described are the same.
http://farm9.staticflickr.com/8112/8565667600_5d15c6573a.jpg