Blade arb deflection

[poe21]

Can anyone tell me how far your blade arb's are deflecting on a full soft setting. My FEA is not being friendly to me. Are you using a hardened steel, or plain steel? I've been searching, but nothing.

[exFSAE]

Hardened or not shouldn't make any difference.

On our older cars you could see the ARB's twist a lot, just by watching the thing go around the skidpad.

[Chassis Man Jim]

What style of blades are you talking about? Is it end to end relation or blade relative to tube?

If you're looking for tube deflection, It's way easier to use excel to do your calcs for different O.D.'s, wall thicknesses, lengths, and moduli.

[poe21]

As of now, using 4130 AISI steel normalized at 870C, I am getting about .45 inches of deflection per side with a 6 in long blade (mind you this is on the softest setting). This brings about a factor of safety of approximately 1.44 at the thin part of the blade closest to the base of the blade. I can't seem to get a whole lot better without jankin up something else. On full stiff, it sees about .28 inches of deflection, and a factor of safety around 2.25. I can deal with that. I may be going about this the wrong way, but it seems more complicated than i originally thought it would be.

[poe21]

I guess what I'm trying to say is how much do the BLADES themselves deflect on a soft setting. The bar takes most of the deflection on the stiff settings.

[Chassis Man Jim]

Looks like the blades deflect about .17 inches.

It seems low, but I really don't know. We don't run that style because of its non-linearity and the mid range bending load it puts on the bell crank.

[Chassis Man Jim]

You should read Think Fast. It's pretty awesome, and Neil talks about those ARB's.

[RobbyObby]

Wouldnt it be specific to the appication/results your team desires. It depends on material (not all teams use steel), thickness of the blade, length of the blade, stiffness of the bar, etc. Every team is gonna have different results.

[poe21]

I'm not asking to try and copy someone's ideas or exact design yadda yadda. I was just looking at it from the perspective of "am I being unrealistic". I mean .45 inches seems like a lot of deflection, and I don't even know what is gonna happen when I start doing fatigue analysis. At the moment I have moved to a 4340 steel as it seems to handle the deflection much better than the 4130. Now... how well can we machine 4340??? Who knows.

[BrandenC]

Good luck trying to find 4340 plate, I looked a lot last year and couldn't find a thing. 4340 is pretty much only produced in round. Just use 4130 heat treated to 135ish ksi yield. Blade deflection is going to vary a ton based on packaging, desired roll stiffness range and desired tlltd range. FEA should get you close to an accurate deflection and linear spring rate of the arb at full soft, but bench testing the actual assembly is the only way to know for sure.

[Bobby Doyle]

Originally posted by poe21:
I guess what I'm trying to say is how much do the BLADES themselves deflect on a soft setting. The bar takes most of the deflection on the stiff settings.

Modeling the components as springs in series (hand calc) should tell you the displacement of each component given an external force or imposed displacement on the system. These results are highly dependent on your own design.