Dart actuator problems

This last weekend in glacier peak we ran into a significant problem with our dart actuators. During the competition we had the small metal gear that drives the plastic potentiometer hear slip. The metal gear would spin freely from the lead screw shaft causing all our values to be wrong. A few weeks earlier we thought we blew out the potentiometer on the dart from our backup bot, but it turns out that it was the same problem. We found that out when we disassembled it for parts during the competition. Needless to say it cost us one match and 2 more matches of having to drive our shooter arm manually which greatly hurt our scoring ability. We tighter the gear and loctited the appropriate threads to ensure the gear would not slip again. We then spend two hours re doing all our potentiometer values for our shooter arm. Everything ran okay for 5 matches until the gear started slipping again and then spun freely in our first quarterfinal match. We reverted to all of our manual override code. We had to run the rest of the competition by manually moving the arm up and down and guessing. Needless to say it nearly cost us the competition win when it went to three matches in semi finals and finals. We were forced to shoot low goals in semi finals to ensure we could capture the tower to win the match. In the finals the number one seed and captain of our alliance broke an axle on their arm so they sat out the first match. In that match we decided to guess and shoot in the high goal because we were then required to shoot and breach the defenses as well. (The third robot on our alliance was having radio issues so they were intermittent) Through eye balling all our shots we made all but two of our shots(one bounced out of the goal) and lost 103-102. The second match our alliance captain returned and we were able to barely squeak out the win 2 versus 3 because our third robot was completely dead the whole match. Match 3 we called a replacement and were able to seal the win. Needless to say the dart gear problem nearly cost us the competition so please check your actuators as well and make sure you don’t have this problem! Just a heads up both of our dart actuators have seen heavy use. The competition boy one that broke ran 1.5 competitions before breaking and the practice bot one ran for many hours of use. We never ran the darts to their minimum or maximum during competition. We have hard stops that prevent that as well as software stops.

Has anybody else had this problem? If so how have you fixed it?

We are planning to put a versaplanetary encoder on our drive motor as a back up to the potentiometer. We have also ordered 2 new dart actuators for our next competition.

In the video you can see us almost grind through the upper stop on one of our early shots. You can see the arm go up and shake a little bit. I misplaced how high I had the arm and nearly broke the actuator because of the potentiometer problem. http://youtu.be/6vSVXhak_Wg

We originally tried to use the potentiometer but after breaking on and the other one being inaccurate, we just took then off. We just put an extra gyro on the arm and use that to tell the angle of the arm.

We had the same issues. The best solution I have to offer is to put way more red loctite in there than you think you need, then tighten it way harder than you think you need to. We also tightened the plastic gear onto the potentiometer with what was probably unnecessary amounts of force after it slipped a little.