Encoder: Can't Find Consistent Values for One Rotation

[joecapps1127]

Hello,
So my team has been working on our autonomous code. We would like to create timing based on the rotations of the wheels. However, we cannot figure out exactly what number is equal to one full rotation. I read many places that it should be 1440, but it is not for ours. It fluctuates from 1210 to 1240 each time we run the code. We need this to be more accurate. We are using standard Tetrix DC motors with Tetrix Motor Encoders. We are using RobotC and are a first year team.

We also tried doing the same thing with time. I.e. running the motor at 100% power for 500 ms is about one turn, but again, it fluctuates.

Our autonomous code kind of hinges on us getting this to work, so any help would be greatly appreciated.

Thanks!