designing a motor assemby for ebike

We have existing motor. The engineer wil calculate what gears are needed. The designer will calculate also the Nm at the end of the outgoing axle. System should be designed, when motor runs it will move chainwheel to let run the bike. But, when stopping pedalling, the motor will ot turn the drancks anymore (in mechanical way). When we do not use motor, we should be able to use the crancks as on a normal bike, BUT we do not move at that time aany part of the motor to avoid reistance when pealling without motor is working. So, should ride than as normal bike.