Using motors to keep slipgear arm still

Without getting into too much detail, we have a catapult robot that can launch across the fence, as well as an intake that places a star into the catapult when the catapult is primed. We’re using a 5:1 ratio, which is the perfect amount to pull back and launch, however when unpowered, the arm backdrives. Is it bad for the motors to put them at a speed that keeps the arm perfectly still, or is this acceptable? We’ve tried a custom ratchet setup, however the elastics force was too strong.

Keeping your motors at a very low power (maybe 10 or so) should be fine. If your looking for a new ratchet, this is the best one I’ve seen. It should work with out elastics, because it uses gravity, and with enough of them it will hold down your catapult.

IMO( I may be wrong on all of this), you would need more power than 10 to keep the catapult in a down position, especially with the amount of rubber bands you have on. Also, you should not keep motors under strain like that for any extended period of time, otherwise you risk burning them out

We are also using a ratcheting mechanism, but it is one that is similar to the one teams used last year on their flywheels

Video of catapult in action:

@4361T Link seems to be broken for the video. Do you have any reference to the rachet youre using? Ours involved bearings and our arm was strong enough to bend the sides 90°

What you need to do is make an if statment that will have the motors at enough power to hold down the catipult if certain controller/sensor values are true.

Here are some pictures of the parts we used. We cut them out of plastic. The idea is to put the smaller clicker pieces on axles right next to the gear with rubber bands, so that when the gear spins one way, they will lock with the gear, and when it spins the other way, the clickers will slide over the teeth. These are the best pictures of the mechanism that I have.

Wow, that is cool but also kinda overcomplicated if you ask me. I literally just have a piece of lexan pressing on the teeth of the at an angle and it works just as well, if not with higher resolution. But whatever works for you…

That is essentially what we are doing, just in a more complicated way, as you said

Also, if the elastics for the arm are parallel when the arm is drawn back, it will be easier for the motors to keep the arm back.

Our robot works the same way. We have had extended practice sessions (30+ minutes) with the default motor power set to 20 and no problems with overheating (yet).

Woah a motor power set to 20 isn’t that way too low.

It’s just a constant value to counteract gravity. Most people set it to when the buttons to control the lift are not being pressed, the lift is moving at a constant rate of 10-20 to stop the arm from falling back to the ground.