Disengaging a motor on a spring powered hurdler

[Kevin Sevcik]

Originally Posted by Peter Matteson

Or you just buy an automotive winch that free wheels and adapt a kit motor to the planetary it comes with. Just fire a pnuematic to lock the winch in and release the free wheel to retract or release.

Originally Posted by Steve_Alaniz

The concept is having two plates that lock and then releasing them, by separation.. re engaging them to start the cycle over...

Um.. In case you missed it... DON'T ACTUALLY USE the Metal Hole Saws!

In fact... forget I said anything!

Steve

See, we too were thinking along these lines last year. The problem is that any of these mechanisms that we found would lock under load whether by design or lack thereof. To the former, I'm absolutely certain that the freewheel on an auto winch is designed to lock under load. Or, at the very least, be very difficult to release under load. Imagine the consequences if you could easily bump the freewheel while using the winch to lift/tow/pull something.

Similarly for the locking plates. Going down the spectrum from profiles that don't lock under load to those that do you have:
1. If you trace an imaginary pencil from right to left along the "hole saw" teeth, it would never have to move to the left to follow the teeth. This triangle-wave like profile gets harder and harder to hold together the more torque you apply. Easy to release, but hard to load.
2. Your imaginary pencil goes straight vertical tracing a tooth. This sawtooth profile is probably the best bet. Dog shifters like the Andymark shifter rely on flat surfaces like this. Holding thing together isn't particularly difficult, but to release them, you do have to overcome the static friction of the two surfaces being pressed together.
3. If your imaginary pencil has to move to the left at some point while you're trying to trace to the right, then you're really in trouble. This profile would lock together very well under any kind of pressure, but would be very difficult to pull apart, as to do so, you'd have to turn either the input or output side by pulling apart hard enough to backdrive it.

So, I think dog shifters and veeery mild profiles in category 3 would work, but they get harder and harder to release as you put more and more pressure on them.

[Peter Matteson]

Originally Posted by Kevin Sevcik

See, we too were thinking along these lines last year. The problem is that any of these mechanisms that we found would lock under load whether by design or lack thereof. To the former, I'm absolutely certain that the freewheel on an auto winch is designed to lock under load. Or, at the very least, be very difficult to release under load. Imagine the consequences if you could easily bump the freewheel while using the winch to lift/tow/pull something.

This can be fixed by "re-working" the mechanism. We made a compact shoulder out of a modified winch in 2005 and never had a problem once we worked it over. It cost us $70 and we had to machine 2 parts (motor mount and input shaft) to get it to work. It's a cheap solution that you can make work with minimal effort if look around.

[chapmatr]

We were thinking of using a gear with teeth missing to pull it back, although that would require a non-winchy device.

[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.