Issues with cascading lift backdriving

Hey CD,

Our team built a cascading elevator similar to a greyt elevator and we’ve been having issues with the motor backdriving. Whenever we lift the elevator, after it lifts the weight of the carriage causes the elevator to fall back down. We’re driving it with a cim at about a 10/1 gear ratio. Any suggestions on how to prevent this backdriving?

This is not a surprising situation given your gear ratio. Most teams will use an encoder and some sort of PID control to make the elevator motor actively hold it’s position.

If your elevator is too heavy, it will require a significant amount of power to hold it’s position and end up heating up the motor to the point of failure. If that’s the case, you may want to consider since sort of spring to counterbalance the elevator. Or possibly a brake to hold it’s position without using the drive motor.

When I was with 340 in 2013 we used a disc brake on our climber.

Consider a constant force spring. They are an excellent solution for motor strain, and when done correctly can cancel out the effects of gravity, leading to very little work for your motors.

McMaster Carr sells them,here’s a link to the 40lb one I have used in the past

Our solution so far has been to replace our cim with 2 window motors. The window motors have worm gears in them so they cannot backdrive. Thanks everyone for the help!

Actually, it’s not the worm gear that causes the window motors to not backdrive. The gearbox has locking pins on it that cause that behavior. You can remove those pins and have a window motor that can be backdriven.

Anyways, I second the disc brake. We stalled our motors on the past two elevators we built, with unhappy results. This year, we put on a disc brake and it’s pretty much the perfect solution. The elevator goes up and locks in position with no movement or sagging at all, and we got a set of two brakes for about $20 on Amazon. Insanely cheap!

Edit to add a picture:

Window motors tend to wear and the locking pins tend to break after a fair amount of use. I Would recommend the brakes or through code.