Abstract: A mechanical backstop is provided which comprises a housing, an input impact gear, a frictional plate, a floating impact gear, and an output impact gear. The floating impact gear is movably mounted between the input impact gear and the output impact gear to achieve transmission. The frictional plate is fixed relative to the housing and disposed at a side of the floating impact gear close to the input impact gear. When the input impact gear transmits a torque to the floating impact gear, the floating impact gear floats toward the output impact gear to separate from the frictional plate and transmit the torque to the output impact gear. When the floating impact gear transmits a torque reversely, the floating impact gear floats toward the input impact gear to abut against the frictional plate and achieve reverse locking.