Testing and Cause of Failure for Encoders and Hall Effect sensors

[ChrisH]

Al, and Mike,

Thanks for the help. The item Mike linked to does look pretty neat and I will propose getting one to our Fearless Leader. We have a plethora of laptops that were surplused by one of our sponsors (every kid on the team gets one as a loner, they remain team property) and they all have USB and meet the specs. Maybe they can be useful for something besides scouting

And yes Mike we do design the sensors into our design.

Last year we had an encoder. The encoder measured the rotation of a jack shaft. The shaft had a gear mounted on it and the encoder had it's own gear. It was mounted fairly rigidly and there was at least 0.015" slop between the teeth of the gears (approx 1/4 tooth). The encoder was buried in the robot where it would have taken major structural damage to be impacted by part of another robot. Shielding destroyed, major bent aluminum, nothing subtle here, 6" of deflection of the outer shell for contact.

We failed three encoders from two different manufacturers before we gave up. Fortunately our programmers followed my suggestion and made it so the encoder was not essential to operation. (always provide a manual overide for all automated functions) It was never determined just what caused the encoders to fail. One of them is still on the robot, but it has been disconnected. I'm not sure the fate of the others or if they could still be evaluated. We looked at using a pot but it didn't have the resolution we needed to be effective.

I have made it a project for the off-season to better understand how to use these neat little toys. As long as they worked, they worked pretty well, but losing 3 in one and a half competitions was a little too risky for us. I'm thinking about going to Vex chain and sprockets for mechanical isolation to make sure the motion transmission mechanism can't impact the encoder shaft. But that won't help if the real problem is power spikes floating around the electrical system, or the shock of being hit by another robot.

ChrisH