Improve the accuracy of the encoder. Build the disc and hub directly onto the shaft of the motor. Many encoders are coupled to the motor shaft, which causes error and can add side-load to the shaft increasing its runout. If the hub-disc assembly is press-fitted onto the shaft, error is reduced. Use laser technology to make the disc. Lasers are rapidly replacing old mechanical manufacturing methods like mills and saws. Lasers that run on linear motors are extremely precise and can hold disc size/track variation to less than 5 microns, easily a factor of 10 times better than conventional methods. This eliminates the need to make mechanical placement adjustment, which includes precision cameras that can detect down to a micron. Reduce the rod runout.