Engine or large motor in front hub, gyroscopic problem?

Discussion in 'General Questions' started by motorbikemike45, Aug 22, 2009.

  1. I have seen gasoline engines and large(heavy)electric motors mounted in bike front wheel hubs. I have a question concerning the weight of such an installation. As we all know from playing with gyroscopes as children, with a spinning weight comes the gyroscopic effect. A heavy engine or motor in the front hub spinning at speed with the wheel must become a gyroscope, which would try to prevent quick turns of the wheel. My question is, could to much weight carried in a spinning front wheel cause so much gyroscopic effect as to prevent or dangerously slow quick and emergency manouvers? I don't know if there is any experimental data, if anyone has experience with this, or if my doubts about the saftey of this set up are unwarrented? Opinions or experiences are welcome.

  2. bluegoatwoods

    bluegoatwoods Well-Known Member

    I suspect that the only difference in wheel handling would come from the weight, as opposed to the gyroscopic effect.

    An internal combustion engine wouldn't spin at all. It would just be dead weight.

    In the case of an electric motor, the heavy part would also be stationary. Only the hub would spin.

    So unless I'm missing something, it shouldn't be a problem.
  3. SimpleSimon

    SimpleSimon Active Member

    Well, yes and no. Conventional rack mount front engines are stationary, with the only significant added mass that acts gyroscopivally being the sprocket. Not really enough to be an issue.

    Electrics are another matter - it depends on the type. With a Currie motor and sprocket, the issue is essentially the same as the rack mounted gas engine. With a hub motor, the entire weight of the electric motor does spin - the hub is stationary. I've no personal experience of that myself, but a typical hub motor probably weighs less that the heavy steel rim of a motorcycle wheel with tire, and since gyroscopic effect increases as the square of the radial distance of the weight from the center of the "flywheel", the relatively small diameter of most hub motors helps to mitigate any such concern. From what I've read, it really isn't a problem.
  4. Okay, that makes sense. There was a gentleman on the forums earlier who had purchased an electric bike with 1,000 watt motors in both hubs and it appeared the batteries were also in the hubs. I was concerned it might be a problem having that much mass spinning with the wheel. A friend sent me an ad for a gasoline engined bike front wheel. It was difficult to tell from the ad, but the engine seemed to turn with the hub while the crank was stationary, like some WWI rotary aircraft engines. I know a little gyroscopic stability can be a good thing, compare driving a scooter with very small wheels to a scoot with much larger wheels and the stability afforded by a heavier larger circumference rotating mass is apparent and welcome. I was just afraid there might be a "tipping point" where the front wheel could become so stable as to make quick maneuvers difficult. Thanks for clearing this up for me.
  5. SimpleSimon

    SimpleSimon Active Member

    The "wheelmotor" gas engined wheel assembly with a stationary hub was a much-hyped piece of, in IT terms, "vaporware".

    Never went into production.