[Jim Meyer]

I believe the play in the drive train you are experiencing has to do with how the drill motor gear box adjustable clutch works.

POOR DESCRIPION OF HOW THE CLUTCH WORKS FOLLOWS

The clutch works by spring loading several balls against the final stage ring gear. For the gearbox to transfer torque this ring gear needs to be held from spinning. This ring gear has teeth that hit on the balls and lift them when a certain torque is reached. Turning the adjuster increases or decreases the force pushing on the balls and in turn the force needed for the ring gear to slip under the them. With the selector in drill mode it seems the torque required to slip the ring gear is larger than moror can produce.

END OF POOR DESCRIPION OF HOW THE CLUTCH WORKS

I think what you are noticing is the fact that the spacing of the teeth on the ring gear is much larger than the width of the balls. The result seems to be around 45 degrees (I'm guessing here) of output shaft rotation before the ring gear teeth contact the balls. This is normal. You might not have noticed this characteristic when your anti-backdrive pins were working properly.

In FIRST last year we eliminated this lash problem by grinding small divots in the ring gear and replacing the balls and spring with set screws threaded into the ball holes. OCCRA hasn't said whether this is legal yet.

I strongly recommend removing the anti-backdrive pins. They have caused many problems for FIRST teams in previous years. I should note they don't seem to cause as many problems for teams with slow ground speeds.

Hope this helps,

Jim Meyer