Project shows workings of many robot motors, with a driver gear attached to an electric motor and a driven gear attached to a wheel or rotating joint. When the gears are new they intermesh closely and the wheel starts moving as soon as the electric current is applied. With age, wear and tear sets in and the gear teeth wear down a bit and an element of slack appears in the system, so that the driven gear doesn't always move immediately the driver gear moves. This slack is called backlash and it needs to be corrected for, to get really precise robot movements.
