Quote:
Originally Posted by Kevin Leonard
The problem I'm having is how to have enough force in that stored energy to lift the 120+ lb robot up and have it a) be able to be held back by something simple, b) have it not be gigantic (weight-wise or volume-wise)and c) have it be relatively safe for students to assemble and test.
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Anything storing ~400 joules of PE is going to be somewhat dangerous to test (and perhaps to build). Depending on how clever you get, four 40-lb constant force springs from McMaster-Carr should get a robot off the ground if you hook them to a strap which you hook over the bar.
Between a ~30" long robot that's ~30" tall, you should be able to preload four of these (
http://www.mcmaster.com/#9293k14/=10ohghg) on a (loose) strap that you lift up to the bar, and allow them to retract most of that 60". Pull a pin (or release a cam) and, uh, shoom!
(Not necessarily the best idea. I think you could go rather lighter if you just used a winch; but you certainly could use these, or surgical tubing, or maybe just some big honkin' coil springs. The key notion here is to hook on while something else is taking the pre-load, then release that something else to let the pre-load lift the bot.)