Disengaging a motor on a spring powered hurdler

[GUI]

Why not mount a winch so it can spin freely, then use dog gears to engage/disengage it?

I like your idea about the shifters. Andymark makes planetary gearboxes that changes the output of a Fisher-Price motor into that of a CIM. Two FP's Into that, into a Gen2 with one of the speeds taken off should be plenty of force to compress a decent spring, assuming a post gearbox reduction. It all comes pre-made, takes little modification, and is actually quite light.

[Tristan Lall]

Originally Posted by jfrank

i don't think you are allowed to store energy (like in a spring)

You are allowed, as long as it's safe. See <R01> and <S01>. (That's a subjective call, and the officials will make their ruling based on design and operation.)

Originally Posted by corpralchee

Don't they make pneumatic cylinders only use air in one direction. Single action acting cylinders I believe... Anyways you could use that to pull the spring back, let out the air and the spring expands.

Those are prohibited by <R89>, because they do not share part numbers with the items on the Free Pneumatics Order Form.

[MrForbes]

We are planning a pneumatic actuated catapult, and will also have to figure out how to unlatch it, because it will start with the cylinders full of pressure, and halfway extended. The latch will have to release the catapult against full force of what will probably be two 2" bore cylinders. However, the cylinders will probably be located relatively close to the pivot, and the latch can be located at the opposite end, so this will give the latch mechanism quite a bit of leverage. We can also add more leverage by making the latch a lever, actuated by a long stroke, small bore cylinder. I think it will work out ok, but we'll see today if we can draw up a design and run some numbers.

also one could use a steel pin that engages two holes in the parts, and the part with these holes could be made of a plastic material, with a low coefficient of friction. This might make it easier release the mechanism. It could be used on a motor design, by having the pin go sideways into a rotating plate. You would want it to be rather large in diameter, to get the force down to a reasonable level.