Suggestions on a good way to get angle?

[BBray_T1296]

Getting a motor with >1000RPM to stop exactly where you want it with 1/4 of a turn of tolerance is not impossible, albeit extremely difficult, especially with various FRC-rules related constraints.

I am guessing you want to stop the output of some gearing system within that tolerance. at that point, your rpm will be significantly slower (not the 5000RPM of a CIM) and accomplishing that task will be orders of magnitude easier, but CIMS (and bag motors, and fisher price motors) are going to be hard to control so precisely unless they have a very high reduction.

We used the AndyMark am-0914 gearmotor with an additional 3:1 (roughly) reduction (total of 213:1 +/-) and only had 1 full degree of tolerance, and we were using a jaguar and PWM. The problem is, under the large load we had, the difference between stalling and running too-many RPM is so small, PWM-wise, that you will find yourself oscillating to no avail.

While only trying to get 1/4 rotation seems easier, It can lead to failure. With a system, if I told the robot to rotate (say, an arm) 2.5 rotations, It would end up very close to 2.5. However, If I told it to rotate 0.25 rotations, 10 times, It may be likely to end up closer to 2.25 or 2.75 without high precision and accuracy.

We had that problem when our robot auto targeting tried to correct when we shot basketballs (rebound rumble). Over the course of the match, the robot's zero (what it thinks is its starting position [actually started perfectly forward]) ended up maybe 10 degrees off. Of course, it didn't particularly matter in that case, It just thought the goal was a little further around than it was, the camera still said it was straight on (and it was).

In a FIRST setting, you don't have all day to run a motor at 2% power until it is perfectly spot on, you have 3 seconds before that defense bot rams you again.