I recently measured two rotary encoders for two motors spinning at the same speed. I have a question. I attached a plot, I will refer to. So my setup I had to motors spinning freely and I decoded the rotary quadrature encoder signal for both motors whilst sampling twice faster, than half the period of one of the quadrature phases. My problem is that the encoders even though they are spinning at the same rate, the left encoder seems to increase much faster than the right one. I took both the incremental counts, and plotted an error vs. a time.
error plot.bmp (227 KB)