This might be a fun time for your team to look at the properties of worm drives.  A unique property of worm drives is that the worm screw can turn the gear but the gear can't turn the worm screw.  So it can provide a self locking mechanism where the motor can drive the mechanism but the mechanism can never drive the motor.

You can put the gears together yourself or you can use a gearbox like http://www.bricklink.com/catalogItem.asp?P=6588 to hold the gears together in a way where they can't skip.  My kids used this gearbox the last two years to control an arm mechanism on their robot.  Like anything else there are pros and cons but it might be a nice mechanical engineering option for your kids to add to their mental toolbox.

Best Regards,
Jamie Diamond

On Wed, Oct 27, 2010 at 10:23 AM, Frank Fenneran - Team #53 Brainstorms <[log in to unmask]> wrote:
We find this to be an issue almost every year (the kids love to carry stuff around in "boxes" instead of pushing).

The only solution we've ever found is to get the item beyond the vertical plane so it sits back toward the body of the robot while moving, then bring it back around to the front to place it down.

The motors don't have a "parking brake" :)

-Frank

-----Original Message-----
From: First Lego League in Virginia and DC [mailto:[log in to unmask]] On Behalf Of Kevin Weaver
Sent: Wednesday, October 27, 2010 10:02 AM
To: [log in to unmask]
Subject: [VADCFLL-L] Common Bone Repair

We are working on the putting the cast on the bone, but the cast is to heavy for our motor.  Is the a way to code the motor to hold the brake until we want it to turn and put the object down?

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