I currently have a 6hp IC engine which I plan on using to drive the rear axle of a go-kart. I want to increase the torque delivered to the shaft by adding an electric motor in a sort of parallel hybrid drivetrain configuration.

What do I need to ensure neither power source is harmed and the torques add as intended? I'm assuming some sort of transmission is necessary but I am unclear on what exact type would be needed since I was planning on the kart having only one speed.

Thank you!

  • $\begingroup$ Have you researched the drivetrains of the various generations of hybrid cars? Plenty of information to assimilate. $\endgroup$
    – Solar Mike
    Commented Aug 5, 2021 at 6:39
  • $\begingroup$ A motor whose rotor is the the drive shaft is generally the cheapest and easiest method. My EE roommate in college did this on his 60s impala. $\endgroup$
    – Tiger Guy
    Commented Aug 6, 2021 at 20:43

2 Answers 2


A differential gear - similar to the back axle of a rear-wheel drive car - might be good. IC engine goes in one side. Electric drive goes in the other. Power to wheels is taken off what would normally be the drive shaft.

It seems to me that this should allow either power source to stall and the other to provide drive but at half speed (if speed of both drives was matched to start with). It therefore would seem sensible to put the gearbox after the differential.

Hopefully this gives enough inspiration to cause you to abandon the project!

  • $\begingroup$ Yeah, just thinking about the idea makes me shudder. OP seems not to realize how complicated this is. Might as well just make it all electric with an engine acting as the generator to charge the battery. $\endgroup$
    – DKNguyen
    Commented Aug 5, 2021 at 1:00

One commercially viable solution is that one of the Toyota Prius. The basic idea is the following (apparently there a few changes over the years since 1997 introduction):

enter image description here

Figure 1: Toyota prius hybrid system layout (source roperld)

Here you can see MG1 and MG2 which can act both as motors and as generators. From what I understand MG1 utilizes this additional speed of the engine to produce electricity by acting as a generator. The electricity is fed to MG2 which acts as an electric motor and provides torque to the wheels.

Additionally MG1 (Primary motor-generator), is used to start the ICE. By regulating the amount of electrical power generated (by varying MG1's mechanical torque and speed), MG1 effectively controls the transaxle's continuously variable transmission.

And MG2 (Secondary motor-generator): in electric only mode is used as a motor to drives the wheels and additionally is used in regenerative braking as a generator to produce power for the battery energy storage while braking the vehicle.


enter image description here

Figure 2: Toyota prius power split system (source nadascientific.com)

Finally , I agree with the opinion that this a bit too much as a project to undertake on its own.

There is a lot of literature on the web, just describing the toyota prius system (and I am guessing you can find a lot more for other cars)


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