How to Lock a motor

[meatmanek]

There are a few solutions.

My preferred solution is to use a positional feedback sensor of some sort (potentiometer, encoder, etc) mounted to the arm, so the controller knows where the arm is, and then use a PID loop. This is the most complex in terms of programming, but if there's an easy way to mount your sensor it can be the easiest mechanically.

The next solution would be to use a worm drive, or a motor that has worm drive built in. The Denso and Keyang window motors are all worm drive, and cannot be back-driven.

The third solution, if you don't want to mess with tricky PID tuning or replacing a motor entirely in an arm, is a brake system.
Here is a picture of another team's brake mechanism:
http://www.chiefdelphi.com/forums/at...9&d=1172112278

You may want to read this thread:
http://www.chiefdelphi.com/forums/sh...ighlight=brake
EDIT: Never mind, you've already posted on that thread.