back-driveable vs. not

[blindguyinanorg]

we used the window motors last year for our fold out pushing arms that weighed 5 lbs+ each. they were place and the bottoms of the arms. we had to reaplace them several times because the load stripped the gearbox.

[NoRemorse]

In theory, you could put a large enough diameter spool so that the 130 lbs of robot weight would break the motor, but then you would not be able to even lift yourself up. If you design the spool and motor combination to actually lift the robot up, then you are nowhere near back driving the motor.

This is brilliant. Pretty simple actually, but i didn't look at it that way. Thanks!

[ShadowKnight]

aye, we also are using the window motors...a combination of 2 actually because we have the weight and we can...less strain on each motor and all...and after running some of the claculations, we can lift approximately 600 pounds with the motors in combination with gearing down the motors. So yeah...that eliminates the need what so ever to build a devise that prevents the motors from back driving and we really have no worries about breaking the worm gear, especially after some of the testimonials afore mentioned.

[Aignam]

If you simply need to keep a platform raised, or something to the effect of that, you might consider keeping a motor running just enough so the torque holds it in place, but does not change the position of said platform, etc.

[Dick Linn]

Just be mindful and use the correct diameter cable (if you are using cable). There is a definite working strength with cable, and it depends quite a lot on how you fasten it and the radius of the attachment used for the cable or whatever diameter pulleys are used. Leave a reasonable safety margin.

A 3/16 inch cable could be used with plenty of safety margin, or you could snap a cable of 1/8 inch or much larger if you don't engineer it correctly. If you have a cable running around a 1/4 inch bolt or something small, do you realize what stress that causes on the cable? Anything less than a couple of inches diameter should be carefully considered, even if you are oly lifting the robot a few times in the course of competition. Do be careful!