vt951

Hey Bill. Why buckling? Are you still at UC? Have access to any FEA meshers and solvers?

2BWise

Buckling will be the most likely failure mode simply because in this load case it has the lowest ultimate strength. You will see when you do some simple strength calculations that the buckling mode is going to have the lowest ultimate strength and therefore you will need to size the tube according to that. It usually is then oversized in bending. Plus due to the load path there should be minimal bending loads, but since the swaybar mount is in the middle of the forward tube it will matter in this case but I don't believe it will be undersized for it..

No longer at UC. Out in the real world now. I would have had access to Ansys if I was still there, but I was never any good with it anyways. If you need help with FEA I may be able to get someone down there to give you a hand.

Travis - sflraver

The "buckling" load put on the control arm, given an infinitely large sway bar, would be equal to the shock dampening less/plus the spring rate. Without a sway bar there is no center buckling force on the control arm so why would you put your main design focus there in order to meet the other design requirements? The two are completely unrelated.

Who works for Amtrak?.. raise your hand.

vt951

Ok, I see what you mean. But, you might have a different design in mind than me. I think shear and bending will be just as important to look at as buckling, depending on the design.

vt951

Travis the engineer hater!

adrial

Soft Springs and Stiff Swaybar will give you your worst case bending load in the a-arm for cornering.

Designing the suspension for a FSAE car I used 1.5G cornering and 1.5G braking and I think also 5G vertical load at the same time for limit loading. This was super conservative. That design was driven by stiffness requirements more than stress though, so high limit loading wasn't causing an unnecessarily bulky design. I would start with a similar load case and work from there. I remember hearing about vertical loads over 5G's for formula atlantic cars smashing the curbs... Luckily the you hit curbs with the inside tire, so it is relatively unloaded and the loads aren't out of this world. I would start doing some analysis and see what you come up with and how it compares to the stock design, to fabcar, to charlie arms, etc...

For a McPherson strut car with some scrub radius, there will also be some steady tension load in the a-arm from simply holding up the car. There will also be a peak tension load from hitting the curbs, etc... This probably isn't a huge contributor but it needs to be considered.

There is also no sense designing an a-arm that is stronger than it's attachment to the chassis ... unless it is that strong in order to meet your stiffness requirement.

Conservatism is the name of the game when you are designing parts that can cause someone to loose their life. Especially if they will not be tested on the bench prior to real world usage.

I hope whoever out there decides to design an a-arm is aware of everything I mentioned! I know I have thrown around the idea of doing it, but it has always fallen by the wayside.

vt951

I wrote the same thing is post #124. Glad you agree. Where is your lack of confidence coming from? We have engineers and racers contributing their opinions about how to best design and analyze a product for their own use.

2BWise

Please explain how the swaybar contributes to a "Without a sway bar there is no center buckling force on the control arm" Buckling is caused by compressive force along the axial direction of the tube. It has nothing to do with the swaybar.

vt951

I think he means the sway bar is what applies a side load in the middle of the tube, which would encourage buckling.

vt951

Interesting how these arms use the early ball joints. What do you guys think of that as an option? Any idea what he charges for these arms? They wouldn't work with the oem caster block, would they?

I think I still like the rennbay performance/track ball joints better, but am open to alternatives.

Cory M

.....

North Coast Cab

They break and need to be replaced every year on a race car, just like the steel arms. Now, they avoid an expensive custom heim set-up whch is nice, but....maybe there is a better ball joint available from another application that could be used.

vt951

Yeah, I know. That arm design is not what I have in mind... just look at the ball joint.

vt951

Break as in wear out, or complete, catastrophic failure (shear or pop out of joint)?

Nice looking 993 in your avatar.

Chads996

already there my friend. Please keep up.

This is version 1. I can post this one, as I am working with a Motorsports designer. We are already up to version 3.





C.