A device, having first and second motor units, for generating a torque on an output member in response to a torque setpoint. The first motor unit includes at least one motor of a first power, or small motor, having a shaft to which the output member is connected. The second motor unit includes at least one motor of a second power higher than the first power, or large motor, having a shaft rotationally connected to the output member via viscous coupler, and computer programmed, in response to a torque setpoint, to power the second motor unit so that the viscous coupler provides a viscous torque conforming to the torque setpoint. Further, in parallel with this, the first motor unit is powered so that it produces the additional torque between the torque setpoint and the viscous torque until the viscous torque reaches the value of the torque setpoint.