Does anybody know of any good COTS worm gearboxes that can not be backdriven (or at least VERY hard to backdrive)?
I looked at the WormBox and the RAW box on Andymark but both of them say they can be backdriven. If there is a way to modify one of these so they can not be backdriven that would work too.
Thanks.
Have you looked at the KOP window motors?
They seem to be un-backdrivable, but don’t have very powerful motors
Here’s an option if you have access to a manual mill.
If you don’t have access to a mill, but feel like driving across the Bay, PM me and you can come use ours (scheduling tbd).
If that won’t work either,these are much more expensive.
Or, depending on the use you could modify something like this.
Lots of options out there depending on your implementation.
The McMaster worms are more expensive from SDP-SI worms, however the latter will need a stage after it due to the 24 pitch size.
From what Ive been reading about the raw box gearbox is that while it is possible to backdrive people were able to load upwards of 6 totes last year with one gearbox before it ended up backdriving. This year unless you plan on lifting about 100 lbs with the gearbox I would say you should be fine. and if you do find yourself trying to lift that much weight I would consider adding in gas springs to offset the amount of weight on an arm.
If you REALLY need something that doesn’t backdrive I would recommend not using snow blower motors, as last year our team found that after a match or two with load on them (weight not electrical) the motors gave out and started to backdrive. they still worked but they didn’t stay in place during our matches. you could also design a mechanical mechanism to not backdrive instead of relying on expensive CoTS items.
The window motors have a pin that locks the shaft automatically when power is removed - the cars need the windows to stay up even if the car is off. The down side of this is they need to be driven from a “SPIKE” and not a speed controller - which uses PWM to pulse power to the motor. The pulsing does bad things to the pin. Also, as mentioned, they are limited drive power (but great hold power).
I’m guessing that you want this for a winch for climbing. We had a purely climbing robot in 2013. Video here, but skip to the middle of the match to see the actual climbing. We used the WormBox for our first competition. Our robot weighed about 130 lb with bumpers and battery. We had no issues with backdrive at all.
We did have issues with the plastic gears in the WormBox. It doesn’t take much at all to break those gears. If we accidentally bottomed out the climbing mechanism, the gears would strip instantly. We went through three sets during our first competition. We switched to metal gears after the first competition, and we had no other issues in the next two competitions.
I would recommend going metal if you want to use a worm gearbox for climbing.
The raw box is pretty hard to back drive if you set it up right. We consistently put 30-50 foot-pounds of torque on it each time we lifted 4 totes last year without backdriving.
We input 2 CIM motors into 10:1 VP’s with CIM output shafts, then ran those into the RAW box.
If you keep the lever arm short enough, the raw box is going to have a lot less torque on it than that.
I cannot speak to the quality of this particular item, but Harbor Freight has a winch featuring a worm gear. You would obviously need to come up with your own interface. HF sells several winches, most of which feature a ratchet & pawl to prevent backdriving.
Bought one of these to play with. It weighs in at 11lbs! With the frame off and just the gears and drum it’s down to 4.5lbs. Some more lightening by replacing the steel drum should make it manageable. A strap to replace the cable and I think it might work. Mathwise, the speed is right and a miniCIM will drive it to climb around 12 inches per second depending on input speed.