pic: 2471's final winch assembly gear side



This is the winch that team 2471 will be using to pull back our shooter. It is powered by a PG71 gear motor that had its original 775 swapped out for an 18 volt version. Then the power goes though two 35 tooth gears from andy mark. This is so the motor can be neatly packed on top of the spool, and so the ratchet has a convenient location.

Color me impressed. That’s a really neat little assembly.

Have you done any testing to see if you can get enough torque out of the PG-71 gearbox? In the past, we’ve had some problems with them failing at high torque loads.

Also, could you give us a bit more info on final ratio/load/travel/windup time/current for the system?

That looks nice, very well integrated components. I wouldn’t worry too much about the PG71, we used two of them to lift our robot up the pyramid last year over 60 times with a 1.5" pulley. If two PG71’s can dead lift 142 lbs over 450 feet in one season, I’m pretty confident that it can pull back your shooter. Then again, how much tension are you pulling back?

Thanks. We haven’t done any testing of the torque output yet. But the numbers say that it will be more than enough power.
The 18 volt 775 stalls at 166oz-in of torque or 10.3lb-in. After a 71:1 gear reduction that’s 735lb-in. Our spool only has a 0.625" radius, so under perfect conditions it should stall producing 1180lbs of force. Multiply this by a rough torque efficiency of 0.75 and you get 880lbs.

Our shooter should take less than 200lbs to retract so the motor will be running in its happy place (about 10,000rpm) which should pull our cable at about 10in/sec. So it should get the job done in a little over 1 second. Of course it’s all theoretical at this point.

How is that ratchet released? is the tension taken off for the release?

Disregard, I see in the other picture you used a cylinder to slide it.

How is that ratchet released? is the tension taken off for the release?
Disregard, I see in the other picture you used a cylinder to slide it.

I think you’ve got the idea, except the cylinder does not directly slide the ratchet. The cylinder just disengages the spool from its shaft, so the ratchet is always engaged.

Interesting. Our 2 CIM worm gearbox with about an 80:1 final reduction with a 1" diameter pulley takes about 3 seconds to pull back our 130 lb shooter. I’d be interested in hearing your results when you test it on the robot.

We did our first tests of the system as whole today. I’d say it took about 2 seconds to retract our shooter. It measured at over 100lbs of force in its current configuration.

We did have an issue with triggering the shifter rod, but I expect that it will be fixed with some lubrication. Like one of our mentors always says “When in doubt, Lubricate!”