Lots of play in Drill Motors!!!

Hello all,
Team Rush hopes all of your robots are in good repair. We on the other hand have a mysterious problem that maybe some of you can help with. When we first set up our motors we noticed that they could not turn with no power to them. We remembered from past experience that there were anti-backdrive pins but we didnt think it was a big deal. We have noticed as of late that when we run the motors there is a lot of play in the trans. It seems to be between the output shaft and the trans. If this sound like something you have seen before please send us a reply. Thanks in advance,
Team 27
Team Rush

I’m not a hundred percent sure what the problem is but if you still have the pins in that may be it. If you need those pins pulled please let us know.

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


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.


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

Justin and Jim,

Thanks for your advice in helping us fix our problem. We actually just replaced the transmission in the motors. It was longer, but might pay off in the future. Thanks again.

Team 27