[Brandon Holley]

Originally Posted by Jeffy

I have been thinking all morning on this.
I still can't figure this out:
I can pull the cable back with a winch and it won't back drive. But when I release the winch the motor will want to spin with the springs.
What I think I need to find is some sort of clutch between the cable and the winch. Any suggestions?

In 2008 we made a "catapult" of sorts to shoot the ball. Here is a picture from the arizona regional of a ball in mid air off of one of our shots(http://www.chiefdelphi.com/media/photos/30965). From our estimates we were winching back around 300lbs of spring force.

Our initial solution was one of the andymark dog gears that everyone here has mentioned thus far. We ran into a problem however when the winch was fully cranked back. There was so much tension in the springs that the dog gear would not disengage. We were using a 1.5" bore, 1" stroke, pneumatic piston to disengage.

We went back to the drawing board and decided to use a ball lock clutch. If you do some searches here on CD for ball lock transmissions you will see that team 222 has quite a bit of experience with them. Essentially how they work is you have a hollow shaft which a gear sits on. The gear has slits cut into it so if you looked at it from the side you would see something like a + sign. The hollow shaft has spots for 4 ball bearings to sit in, so that when they are placed in the shaft, the gear spins freely around the ball bearings. You then actuate a rod inside of the hollow shaft so when the rod pushes through the shaft, it forces the ball bearings into the slots cut in the gear.

This was a very effective system for us, and will be something we use again if we ever have to winch something back and then unload it quickly.

-Brando

PS- obviously if you have any questions feel free to ask