How do I lock my arm motor when climbing?

[CajunVoltageVipers]

Usually the motors just lower the bot when the driving stops. Is there a way to lock the arm motor when the comp driver control period stops, to prevent the bot from losing its climb?

[23218F]

You cannot do it programmatically unfortunately:

How to lock the motor at the end of the field controller!

When a field controller puts a robot in “disabled” mode (after a match ends), it will force all v5 motors into “coast” mode (preventing any voltage commands from being sent to motors). This is enforced on a vexos level and it’s not possible to legally circumvent it. If you need to prevent a mechanism from turning after the match ends, I’d recommend something like a high torque ratchet or pneumatic clamp rather than relying on motor braking.

Therefore you have to do something to physically stop it, i recommend using a pneumatic to lock a gear of similar:

How to lock the motor at the end of the field controller!

I posted something like this during may here’s the answer [Vex Toss Up High Hang Lock V2.0]

I guess you could use a ratchet, but that really depends on use case, and yours sounds like it wont work, since i imagine to climb your arm has to move both ways and not lock during use. You could use a ratchett and engage and disengage it using pneumatics similar to the first idea.
Let me know if you need anymore help

[Steeltron0419]

When a robot is disabled at the end of a match, the motors are set to coast. In order to prevent the bot from losing a climb, you’d have to come up with a locking mechanism.

[Team90235A]

You can set the motor to hold. It depends on the weight of your robot but you can also use an 100rpm red motor to increase torque and then set it to hold.

[15981A]

If you look at teams like gremlin they use use hooks. So the motor pulls up the robot and it it rests on the hooks. But i would suggest trying a passive hang by just driving on the ladder. Thats what we do. Depends what your going for.

[Steeltron0419]

setting the motor to hold wouldn’t fix the robot dropping when it is disabled, as disabling sets all motors to coast automatically.

[technik3k]

The simplest way to lock your mechanism when electrical power is no longer available (to hold motors) is, probably, to have some custom hook or ratchet that engages at the end of the climb. This works well if you have a single final destination and don’t need to move after that any more.

More complex, but reversible mechanisms may be based on some sort of pneumatics to engage and disengage external brake.

However, there are ways to achieve similar reversible functionality that doesn’t rely on active pneumatics or motor power purely by mechanical means.

One of them is to use worm gear, which cannot be backdriven. The disadvantage is that you need to go through very high speed gear ratio first, which leads to high friction losses, and VEX worm gear and wheel are not as strong as the regular high strength gears and are quite fragile.

Another alternative would be to create a non-linear variable ratio gear train. Here are some examples:

As you go through the full rotation you move with quick gear ratio for the most part of the cycle and then have a slow gear ratio for a small period of time. You could tune those gear ratios such that during this last phase even the large resisting force on the output side will not be able to overcome and backdrive even the tiny natural friction in the unpowered motor on the input side.

Advantage of this method is that you could have a number of natural stop points along your climb. And the disadvantage of this method is that you have to make custom gears, destroying quite a few HS gears in the process, before you get it right.