I am a bit puzzled by something I've observed with a DC motor I am using and was hoping someone could offer insight.
I am working with a Maxon A-max 26 DC motor which is equipped with a 100-count per revolution encoder. I got it used on eBay, so it's one-of-a-kind (at least for me). In measuring motor velocity, I've noticed that there is a point once per cycle where the motor appears to speed up slightly from about about 1/3rd percent of its average. This measurement is very much repeatable (I've tested it over hundreds of revolutions) and always happens at the same position. This happens when running the motor at a steady rate, of about 3370 RPM, after coming fully up to speed. The motor is running unloaded, except for the power loss through its gearhead. I am trying to get parts for a flywheel so that I can put some momentum on the thing to see what difference it makes.
Clearly, the variation isn't that serious, but it does annoy me that I don't understand its cause. I can think of two possible explanations. Some kind of mechanical or electromechanical issue (cogging?) or a slight inaccuracy in the encoder. Does anybody have any ideas as to what might be happening or what I can do to isolate the problem?