A single pinion drives the axis (the "learn") whilst the second pinion is "preloaded" to eliminate the backlash (the "slave"). The preload is designed electronically by using a Specific motor controller; these devices can even be put in place to travel jointly through cycle occasions when backlash just isn't vital. https://cristiantncqd.laowaiblog.com/31769123/getting-my-gearbox-cvt-to-work