Abstract: Pedal power provided by the driver is delivered to the drive wheel of a vehicle, aided when necessary by an electric motor and transmission. A second electric motor adds regenerative braking functionality and the ability to drive the vehicle in reverse. The second motor may also be used to drive the vehicle forwards, and power to the two motors may be split to optimize the efficiency, torque or power output of the drivetrain system. A freewheel mechanism allows the vehicle to be driven forwards by the first motor without back-driving the crank. An optional second freewheel mechanism allows the vehicle to move forwards without back-driving the first motor and the crank.