Reducing Friction in Shooter

[mott]

Originally Posted by Dr.Gusta

We just wrap the rope around the peice of 1/2" hex shaft. We use the high torque third stage offered by VEX for their ball shifter and I measured it with a fish scale attached to the rope and unspooling the rope by pulling on the scale. It read out 14lbs consistently.

Hearing this, the one immediate suggestion might be to try to use as large of a "drum" as you can to wind up your rope. Obviously, this would impact your ratios but unspooling a tiny drum is harder than unspooling a larger LIGHTWEIGHT drum.

[Conor Ryan]

With all misconceceptions that everyone is working through, I have a vauge idea what we are trying to accomplish.

So you have a couple of options:
1) Go with a larger diameter spool. 1/4" is really small, 2" probably will do the trick. You want to minimize the amount of revolutions you do on the spool.

2) Tie some surgical tubing to "Spring Load" your spool. The idea is that as you wind the winch back, you pull on the surgical tubing more. Spring force is translated to the unraveling of the spool without using the force to catapult the ball.

3) Make sure you follow the 45 pound withholding allowance rules.

[mott]

Originally Posted by Conor Ryan

2) Tie some surgical tubing to "Spring Load" your spool. The idea is that as you wind the winch back, you pull on the surgical tubing more. Spring force is translated to the unraveling of the spool without using the force to catapult the ball.

Isn't this the same as having more spring power on the shooting mechanism itself?

Maybe I'm misunderstanding this suggestion...

This is a reasonable solution if the drawback motor/gearbox has additional pulling capacity over what they are currently using but I assumed not.

[Conor Ryan]

Originally Posted by mott

Isn't this the same as having more spring power on the shooting mechanism itself?

Maybe I'm misunderstanding this suggestion...

This is a reasonable solution if the drawback motor/gearbox has additional pulling capacity over what they are currently using but I assumed not.

The main difference is you anchor it to the frame rather than the catapult arm. This allows you use one set of spring force to overcome the intertia of the shooting arm, and another set of spring force to overcome the intertia of the winch being wound back.

All in all, this is fairly useless unless you can move to a larger winch spool diameter, 1/2" is not enough you should go to at least 1", ideally 2"

[mott]

Originally Posted by Conor Ryan

The main difference is you anchor it to the frame rather than the catapult arm. This allows you use one set of spring force to overcome the intertia of the shooting arm, and another set of spring force to overcome the intertia of the winch being wound back.

Ok, I understand what you're saying but assuming your overall "load" on the motor/gearbox is limited to some maximum, wouldn't you be better off attaching ALL of the springs directly to the launcher so that every bit of energy not needed to overcome the inertia of the winch would be available to put into the shooting arm (instead of being wasted pulling on a frame member)?

[Chris is me]

Originally Posted by Conor Ryan

All in all, this is fairly useless unless you can move to a larger winch spool diameter, 1/2" is not enough you should go to at least 1", ideally 2"

This is probably obvious, but I just wanted to make clear to the OP - increasing the winch drum diameter will increase your speed at the expense of torque. Think of it like the opposite of a gear reduction. That said, the greater diameter the winch drum is, the greater torque your spring force will put on the output shaft upon release.

A quick and dirty way to make a bigger winch is to throw some hex hubs on the shaft, the kind normally used for sprockets and wheels.

[JamesCH95]

Does your spool have sides on it that rotate with the shaft to contain the cable/strap/cord?