Hey guys my first post here. I was planning on building a motorbike that you can also pedal like a bicycle. The idea is that you dont have to have a license if the IC is under 50cc. So the plan is I want to have a hybrid powertrain consisted of a 50cc 2stroke(7kw) IC and a 1kw electric motor. The quetion is will the torque add from the two sources or will one always pull while the other will be getting pulled struggling to keep up? Is it necessary to have the two sources connected to a differential for them to work together?

  • $\begingroup$ have you looked at any "how it works" pages for the Toyota Prius? $\endgroup$ Dec 8, 2016 at 14:29
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    $\begingroup$ en.wikipedia.org/wiki/Hybrid_vehicle_drivetrain $\endgroup$ Dec 8, 2016 at 14:42
  • $\begingroup$ So from your description of the problem there would be three power sources: Pedals, electric BLDC and the IC engine. $\endgroup$ Dec 8, 2016 at 16:33
  • $\begingroup$ Is the expectation that the IC engine is the primary source, electric to assist and electric+pedals to assist? Is there a situation where pedals only provides motive power? The reason I ask is because the drivetrain becomes complex with clutches and gearing to consider. Simply stated the BLDC torque will add to the IC torque through the appropriate transmission. The BLDC motor could be controlled in a manner that responds to the IC motor performance and therefore assist. $\endgroup$ Dec 8, 2016 at 16:38
  • $\begingroup$ My original plan was this(although very complex). The motorbike will have an IC (controlled by throttle) , the pedals will never work by them selves, there will be a system like the Bosch Performance Line CX (as it will be very difficult to pedal without the IC because of the weight of the system). Also there will be an electric motor at the rear hub that will have regenerative braking(controlled by throttle in sync with the IC).The batteries will be charged when braking via regen. braking or by the IC.The question is how can the motor at the rear hub will be able to work with the IC? $\endgroup$ Dec 8, 2016 at 19:36

1 Answer 1


It might make more sense not to have the IC engine delivering power directly to the wheels at all. Rather just use it to generate electricity to power the motor and charge the batteries. This approach has number of advantages.

  • You eliminate quite a bit of mechanical complexity in the transmission as you don't need a variable ratio gearbox or sophisticated clutch and avoid coupling two different motors into the same drive train.
  • The IC engine can either be running at its optimum RPM or off, improving efficiency.
  • You will get better low speed torque which is good for a moderately heavy bicycle.

In this case you might want to look at a less powerful IC engine and a more powerful electric motor.

So for example you might have various different conditions.

1) Constant speed on the flat : ICE running powering the motor and charging the batteries EM providing motive power.

2) Uphill/accelerating : ICE engine powering motor with extra power provided by the batteries.

3) downhill : ICE off and EM in regenerative mode.

4) electric only : ICE off and EM in battery mode.

This setup also give you a bit more flexibility as to how you package and place the main components.


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