adrial

It's time to start doing FEA iterations.

I think your previous design would have worked well if you tied an upper and lower plate together with a cylindrical boss (which would contain the bushings). Although the latest design is easier to manufacture since less jigging is required.

Remember you are trying to take out bending... moment of inertia (strength) goes up real fast (^3 fast) as you increase height or diameter.

vt951

Adrial,

I took some of your suggestions. I'm feeling pretty good about this design, as it does not rely strictly on the welds to carry bump load and is much stronger in bending. Also, the sway bar mount is reinforced and is located at the correct height (in plane of the other 3 mounting points). And, I've incorporated a 7.5 degree bend in the end section to correct for a 2" lowered suspension (prevents binding of the ball joint). Note that the ends of the tubes would be capped on the real part, I just didn't model that.

PorscheDoc

I may have missed it somewhere in the post, but are there longer ball joint pins available for this potential setup? Figure most guys upgrading control arms are probably tracking their cars, and have in turn lowered them. Just curious.

vt951

It was mentioned earlier in this thread, and I don't know the answer yet. I am not sure if the early ball joints can be modified to accept a longer pin.

I'm not sure what the longer pins buy you, though. I've heard that they cause bump steer.

inactiveuser92616

Good luck! That's going to need some precision manufacturing for everything to be in the right place after fab and welding, while staying within your price point for small batches. I wonder whether it would be more economical to create an aluminum sand casting pattern that uses the early ball joint; but you already have this designed so try it first.

I would recommend not including holes in the plasma cutting pattern. Plasma/waterjet get oddly shaped and rough holes that aren't really suitable for tapping. It is easiest to drill these after the part is cut out.

vt951

patrat, thanks for your suggestions. I think you're right about the tapped holes. We will probably drill those rather than cut them out.

I don't think the fab and welding will be a problem, but I have yet to show this latest design to the fabricator so we'll see. I know he plans to make jigs to hold everything in precise location during welding.

The aluminum cast a-arms don't hold up well in the higher loads of racing, so that's part of the reason for making these out of steel tube. Early ball joints are just a way to keep the costs down (up-front and maintenance).

vt951

It's been a while since I've updated here, but we have continued working on these. I think we'll have the first set done and installed on my car in about a week to do some testing.

The FEA results look good (after a few design tweaks). I calculated loads based on the conditions discussed in this thread... 1.5 g cornering, 1.5 g braking, and 5 g bump. Even with all those forces acting simultaneously, the stresses stayed below 55 ksi. Yield strength for chromoloy is about 63 ksi, so we have a little bit of safety factor as well. The bump load created the highest stresses. However, I calculated them based on full deflection of a moderately sprung car (250 lb/in front springs) and a heavy sway bar (30 mm OD). Bump loads on the control arms will actually be lower on a car with stiffer springs, because there will be less deflection before hitting the bump stop, which creates less torque on the sway bar (and therefore less force on the control arm).

The prototype set uses adjustable end links on the inboard side, to allow improved adjustment of camber and caster. There are "plans" for a lower cost version of the arms with fixed ends as well. The prototype is just tack welded in the pic. I will post pics of the completed welds when they are done.

We have been in touch with 944 Cup about marketing these. At least for now, rennlist sponsor costs are too high for this single product. Maybe at some point in the future it will make sense, but not yet. 944 Cup is definitely the target market for these anyway.

Before anyone asks, these are not for sale yet. This is merely a prototype set for my car. I don't even know what my brother in law is going to charge for them. If you want more info, please PM me, and I'll let you know if and when there actually is a product and where you can get it.

Lorax

I want some.

fbgh2o

Wow Alan... These look awesome...

vt951

Cool. Will let you know when they are available.


Thanks Fergus. I'm glad they don't look too agricultural ... they are definitely a "form follows function" design. I might see if he can make the two end links parallel in the future, just for looks. They are spherical joints, so that doesn't really matter functionally, but it would look better.

xsboost90

just purchased everything to convert my car to late offset- lemme know when you make a late offset pair and i'll "try them out" for you.

vt951

Will do.

Late offset? What are you going to do with those speedlines then? You are always looking for an excuse to get new wheels, aren't you? Are you going with big blacks or reds also?

EDIT: I guess the speedlines are late offset, so that didn't make much sense did it.