[FTC]: TETRIX DC Motor Gearbox issues

[Wingus&Dingus]

So we've broken a couple of lift arm motors.... both V1 and V2. Mostly gearbox destruction.
We're reasonably confident everything we can do to prevent this happening has been done but we struck a new issue this morning.
If there's a loss of control due to communication issues sometimes motors get left running at whatever power they were last set to and with our lift arm that's not a good situation. Under normal circumstances the arm won't ever hit the mechanical stop points at full power (actually it's limited to +-70) and there's position feedback and limit switches so all is well but if communications stops we can quickly end up with another busted gearbox.

Do we need to manufacture a clutch so there's a last ditch mechanical safety system?
Has anyone else struck a similar problem and what did you do about it?

[TRWSHSHLX]

If you have position feedback / limit switches, program the lift such that if the limit switch on top is hit (when the lift is at maximum height), it can only go down or stop.

The second way is to go into one of the default files (some other team did it and posted the code on here before - I will try and find it) which adds a logic that says if data isn't refresh in a certain amount of time, it sets all the joystick inputs to zero / default.

EDIT: here (http://www.chiefdelphi.com/forums/showthread.php?t=94102) is the link with said thread.

[Andrew Lobos]

If you have position feedback / limit switches, program the lift such that if the limit switch on top is hit (when the lift is at maximum height), it can only go down or stop.

The second way is to go into one of the default files (some other team did it and posted the code on here before - I will try and find it) which adds a logic that says if data isn't refresh in a certain amount of time, it sets all the joystick inputs to zero / default.

EDIT: here (http://www.chiefdelphi.com/forums/showthread.php?t=94102) is the link with said thread.

In the event of a NXT brick lockup or motor controller freeze (due to a bad battery connector or brownout), the only solution that guarantees safety of your robot is a mechanical solution.

[Wingus&Dingus]

Thanks for the responses. We've implemented a mechanical safety to minimize shock loads on the gearbox. Ended up testing it by mistake today after accidentally disconnecting the arm position feedback! No more broken gearboxes.