So my team has been searching around CD, and i know i have seen a post saying how to make a winch type motor. My team is looking to use either a window motor, banebot motor, cim, or a FP motor, but the question is how to we keep it so it doesnt just let the arm drop freely?

It depends on motor type. Also, the term you’re looking for is “backdrive”.

Window motor: Backdrive protection is built in. It’s got a worm gear in the gearbox, and worm gears really don’t like backdriving. Can you do it? Depends on the worm gear, but you really have to work at it.

CIM: I’d recommend keeping 4 CIMs in the drive, and we only get 4 this year. (It is also possible to use 2 CIMs and 2 FP.)

CIM, FP, or Banebots: Start by setting the speed controller to “brake” mode. Beyond that, it’s a question of gearing and what sort of brakes you’re putting on. I know 330 didn’t have much of a problem with an FP-stock gearbox-2-stage chain/sprocket reduction (not sure exactly how big) when that was used in 2005, 2007, and 2008. It could be backdriven, but you had to work at it a bit–say, pull down hard. Under power, it could lift a high schooler. You could also put a pin through a motion part into a solid piece of robot to act as a brake.

A few more specs on the arm might be nice, like how much torque you expect the arm itself to generate when straight out and not moving.

I suggest the window motors, they are really nice and torquey, I think you’d be hard pressed to make it stop if you are using it as a winch. You’d be more likely to snap the cable i believe.


The window motors have 1501 oz-in of torque. This means that at 1 foot away from the center of rotation of the motor you could lift 125 ounces or just under 8 pounds. being a winch you’re never more than a few inches from the center of rotation so you at its weakest point you’d probably get about 47 pounds of force.

Torque is not everything. Power is. You can make any motor in the KOP have enough torque to lift any FRC-type load… but it might take a long while if it doesn’t have a lot of power.

For the record, Ethan, I’ve seen two (older model) FP motors with stock gearboxes and a 3" or so diameter winch lift an entire robot, 130 lb with battery and no bumpers, up to 10’ in the air in about 2 seconds, 4 if you include raising the lift. I don’t remember those two breaking much cable–but they sure bent the (aluminum C-channel) lift when driven down when it was at the bottom! They were locked in place when at the top by a shifting-type pneumatic cylinder fired into a notch on the winch.

A window motor doesn’t have a lot of speed necessarily. Sure, you can have them give 120* of motion in a split second with no reduction–I’ve seen that done too, on a low-weight, low torque application. But use them to drive a robot? Nope, too darn slow despite all that torque. It’s been done.

The primary considerations are: How fast does the arm need to move? How much torque is the arm exerting, approximately? Then you want to consider: Where is your motor planned to go? What motors are already committed elsewhere? How much of a safety factor do you want? (For the cases where somebody decides to use arm-arm contact to keep your arm down. It can happen.) Do you want the arm to double as a robot-righting device? Hey, it could be quite handy if either you or a partner goes down.

okay we are using a forklift style arm, it gets set up by pnuematics, and we have this 10-15 pound manipulator that has wheels that just let it move up and down really nice, but my question is that if we use a winch, every time that we let it down to the bottom to pick up a tube, we want to be able to push a seperate button to go to a distinct peg ie: push button 10 and go to the top peg in about 4-5 sec. We are leaning towards the FP gearbox that came this year, we just dont know how to hook anything on it, we were going to attempt to use a window motor, and we couldnt find a way to keep power to it because we are lacking the plug to go in it.

You can’t get plugs for them. They don’t exist unless you wish to order a set of 1000 of them. What we did is we soldered on wires and filled it with epoxy to keep them from getting ripped out.


FP gearbox: If it’s a large black monster like I think it is, you cut some nice solid stock (wood or metal, metal preferred) into a hexagon the size of the inside of the output. Use a hose clamp to lock the teeth around the hexagon. You’ll probably want an axle hole in the center of the hexagon.

Now, you make your winch and attach the winch to the hexagon. How this is done is left as an exercise for your team. There are resources on CD and in other places.

If you’re really savvy, you can figure out how to use a servo or pneumatic cylinder to act as a locking pin so you can stay in any given position for as long as you need to (i.e., go there, lock, unlock before moving).

So we are planning to take advantage to this pneumatic lack of rules this year, so is there a way to control our pneumatics after we fill up all of our max of 4 (in our case festos)slots to extend and to retract the cylinder? like what way can we control a cylinder after we fill up our little thingy on the crio in like spot 7 or 8?

Spikes to solenoids work reasonably well. That’s what we used before breakout boards… cRIO (or back before the cRIO, the IFI controller) tells the Spike to switch, the spike switches, and the solenoid does whatever it’s supposed to do. Note: you will need a 12V solenoid for this setup. Or a 12-24VDC converter, preferably between the Spike and the solenoid so the Spike isn’t blown.

See the pic below for a winch that worked quite well for us. It lifted our three stage fork lift to a height of 11.5’ in under 5 sec. We had way more than enough torque and we were using a drum (spool) of about 4". They were the stock FP’s for that year, but I’m sure that the 550’s would work quite nicely.

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