My team has come up with ideas for stopping our climb mechanism from releasing our robot at the end of the match (lowering to the ground). Does anyone know if at the end of the match does power get cut from the motors if you put them in brake mode. Our climb gearbox uses two neos and we were thinking of having them on brake mode at the end of the match. Would this work at the end of the match or do we need to use something else to physically jam the gearbox at the end of the match?
Power gets cut from the motors no matter what (legal) things you do. However, brake mode does not draw power to “hold” the motors in place – rather, it shorts the leads of the motor together, which (in simple terms) causes the motor to be harder to spin.
If brake mode + the friction force that must be overcome to backdrive your gearboxes is enough to make the robot not fall, this could be a viable option for you.
If not, we’ve had success using 2 40lb constant force springs pulling our climber down, which (in addition to our 10:80T reduction and brake mode) make the robot stay up quite well.
Having your motors in brake mode will not prevent your robot from lowering back to the ground. What a lot of teams do is use a ratchet of some sort, whether it be a versaplanetary with a ratchet or a ratchet wrench.
So the braking force of your motors depends also on your gear reduction. The more reduction the more it will hold. I’m unsure how a falcon and a neo hold against each other in terms of their braking power. But when we climbed with our bot and just disabled to see what would happen, it took the robot (122 lbs) about 8-10 seconds to fall 30in in break mode. With that being said i do recommend a breaking mechanism, either a ratchet or a friction break. WCP friction break. I would recommend a break that can be disengaged just in case you miss them bar you aren’t out of luck.
You should use some type of braking mechanism. It can certainly be a ratchet, as noted by @TristanB, or you can use a positive stop of some other kind. We’re using a pneumatic cylinder to engage a dog gear that locks our winch in place until the pressure is released. Whatever you use, make sure that it doesn’t depend on continued electrical power, since you won’t have it.
If needed all you have to do is take a ratchet wrench and a stop bolt. When you climb up it spins freely but when you pull down it starts to ratchet. When power is shut off the wrench hard locks on the stop bolt and your robot will stay up until you take it down. A big down fall is you only get one try. But it’s an easy fix if all else fails.
Can you explain this to me. We have system where the elevator goes up and then comes down with the same motor. How would you have a ratchet allow you to go up and down but not up again without motors.
Well you actually can, look at what Everybot did. You wound your rope up in the way so that as you spin the motor freely with the ratchet it unwinds the roping, then causes the lift system to move up (powered by springs) then as the lift reaches its top of travel, the rope is fully unspooled then begins to spool back in the opposite way causing the lift to be pulled down.
I’m late to this conversation but I wanted to give some experience. We use Neos in breaking mode for our lift. Braking mode works depending on the gear ratio. Higher the ratio, stronger the braking. Our lift uses 36:1 and it holds our 150lb robot.
When your robot is disabled, it cuts signal to the controllers, not the power, so the motors are still getting power for braking mode.
My understanding of brake mode (at least in the CTRE ecosystem, but I’d expect it to be universal) is that the motor leads are internally shorted together with the H bridge to resist motion; no electricity from the battery is used in brake mode.
Again, all my current understanding; worth double checking.
Good question. I’m not sure, that would be a RevRobotics question.
I know if the SparkMax loses power, it won’t brake. If I unplug the CAN wire from the SparkMax, it will still brake.
On a side note, that caused us a problem once when the CAN wire came out of one side of our lift. One side was breaking while the other side was trying to drive.
I could imagine that power is required to change connections in the H bridge to short the motor leads, and without power, it defaults to all connections open.