Crash Atten. Mounting

[rjwoods77]

Hey everyone,

I have a quick question about attenutaor mounting. We have the design all done and tested on our attenuator but we now have to fix it to the frame. The rules are very loose about the off axis collision and all so I dont know how robust it has to be. We were currently thinking of using a .125 alum. plate bonded to the attenutor and then using four 1/4-20 bolts with 1" OD fender washers to fasten it to the front bulkhead that has threaded bosses in it. I figure 4 1/4-20 bolts in single shear should do the trick but I really have no idea what the judges are going to cream us for and I want to finalize the mounting so we can move on to the next thing.

[rjwoods77]

Hey everyone,

I have a quick question about attenutaor mounting. We have the design all done and tested on our attenuator but we now have to fix it to the frame. The rules are very loose about the off axis collision and all so I dont know how robust it has to be. We were currently thinking of using a .125 alum. plate bonded to the attenutor and then using four 1/4-20 bolts with 1" OD fender washers to fasten it to the front bulkhead that has threaded bosses in it. I figure 4 1/4-20 bolts in single shear should do the trick but I really have no idea what the judges are going to cream us for and I want to finalize the mounting so we can move on to the next thing.

[Mike Cook]

Rob, last year we bonded our honeycomb thing to a .125 aluminum panel and bolted it to the front bulkhead. Just yesterday we were whacking around with some big steel and decided to whack the crush zone. If you sat it on the ground the thing was solid and worked as it should. The second i supported it like how it would have been on the car the aluminum plate just bent to hell. Yes tech let it slide last year, but had we actually hit something like a pole, the whole thing would have just pushed through the front bulkhead. I'm not really saying anything except be thoughtful on how you mount it.

[CMURacing - Prometheus]

the way i see it, we know the crush strength of the honeycomb. so we should use a backing setup that has a higher buckling/shear modulus than that, right?

[Mike Cook]

well, yes. But you know, the backing plate/structure weighs something. So there are ways to get through tech with a lighter setup, although it pratically negates the purpose of a crush zone all together.

[CMURacing - Prometheus]

that's what i'm looking at. the report guidelines talk about off-axis impacts, and secure mounting to the frame. so i'm pretty sure the tech inspectors want to see something that won't fail, and if its iffy, they may ask for backup. the design judges probably will too. so i'd like to have a solution that works. we're probably going to use a thin-gauge steel backing plate, with some more support at the front bulkhead. it'll be beefy, and heavier than .125" aluminum plate, but it should work in a crash.

[drivetrainUW-Platt]

A simple X in the front bulkhead would help a ton, use some 3/8 or 1/2 tubing to make it or something light, that way you have center support for your mounting plate