pic: Encoder Graph

[wireties]

Remember the servo is not strictly a software system and/or a ideally-behaving mechanical system. The mechatronic systems play a significant role in the feedback. It is possible to have mechanical behaviors for which the servo cannot compensate. Plus your encoder values may require low-pass filtering if they are noisy for some reason.

Applying 35% power means nothing really (especially if there is significant delay in the mechatronics), are you trying PID control? Try the PID with a very small proportional gain and see if it cleans up a bit. Then play with the P and I terms (starting with I about 10% of P) and tell us what effects it has on your control.

Nice job collecting data!

HTH