Drop Tower Design & Getting 660 lbf

[Johnny B]

My school does not have any sort of device capable of holding up or dropping 660lbf. I'm probably going to end up using a cherry picker to lift up the weight and release it this year, but anyone got any good pics of a drop tower, perhaps even components/plans for one from your school?

Also, how is everyone coming up with their 660 lbf? Wish we could just use last year's car but my teammates keep complaining about me destroying it. Boo hoo.

[Johnny B]

My school does not have any sort of device capable of holding up or dropping 660lbf. I'm probably going to end up using a cherry picker to lift up the weight and release it this year, but anyone got any good pics of a drop tower, perhaps even components/plans for one from your school?

Also, how is everyone coming up with their 660 lbf? Wish we could just use last year's car but my teammates keep complaining about me destroying it. Boo hoo.

[absolutepressure]

Can't you borrow some weights from your gym? I wouldn't use a cherry picker, they're not designed to do stuff like that.

What you could do is rotate the problem 90 degrees. You could pull/push your crush zone (fastened to a weighted cart) towards a sturdy structure. Now I don't mean the wall of your engineering building, I'd suggest throwing together a strong steel triangle frame that looks like what they put at the end of railroad tracks (looks something like this: _/1 ). Maybe just like 25"l x 15"w x 15"h, or however big your crush zone is. Then, spike that down to a parking lot (they do it all the time to set up tents for tent sales).

After you have that set up, you can decide how much weight you can get, and from that, how fast you have to pull/push it. If you pull it, make sure the vehicle (if used) pulling it is doing so via a small, snappable rope.

Come to think of it, mythbusters does that kind of stuff all the time. They use cheap, easily attainable materials, and get great results.

Sand bags are also good for weighing stuff down.

[Wright D]

If you can find an old hip sled, or someone willing to lone you theirs, then you could use that. It is almost a ready made impact testing rig.
http://www.yukon-fitness.com/Merchant2/graphics/00000001/HLS-2000_1.jpg

Simply remove attractive girl, and insert item to be crushed. Add weights and accelerometers as needed.

[Schumi_Jr]

I'd recommend doing a quasi-static crush on an Instron. You can measure the acceleration (force/mass) and will likely get much more consistent results than dropping a sand bag.

[Johnny B]

I def. have access to an Instron machine, I just didn't realize it could give us the ride down data. I'll think about how it could, but mind giving me a few pointers on that one. Whether I just do a large input force with known displacement or what?

[chavez]

commenting on the picture above, do you know how much weight you would have to put on that sled to recreate the test data. Just for your info we are using 340 lbs dropped from 16 feet http://fsae.com/groupee_common/emoticons/icon_smile.gif.

[RStory]

An Instron will give you force as a function of displacement, so you can say ma=f(x), I think from there I'd just solve it numerically using the data from the instron.

Depending on the attenuator the instron test might not be all that accurate, since it's a nearly static crush instead of a 15mph impact. I still think it's a good test to do though.

I also like the idea of attaching the attenuator to the 2005 car and driving it into a wall, it is hard to convince others that it's a good idea though.

-Robert
Oregon State

[Wright D]

Some hip sleds can hold in excess of 1200 lbs, and the carriage weighs about 200 lb (my estimate). I have no idea why they would need to hold so much weight, but they do.

If you use the full length of the sled you might get a vertical displacement of 4 feet (assuming you don't add any more angle to the sled). Let's say you could get 5 ft out of it safely by tilting the sled up more.

PE1 = 340(16)32 = 174080 (from above)
PE2 = 1400(4)32 = 179200
PE3 = 1400(5)32 = 22400

The friction in the sled might account for the additional energy.

I am by no means saying that this IS the solution, but just another possibility. It might be a machine that is easy to set up, easy to change the PE of, and easy to get repeatable tests out of.

Plus the thing looks a lot like a shrunk down FIA test rig.