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I Estimating cyclette power

  1. Jul 3, 2017 #1
    Hi all!

    I have a cyclette with 8 resistance levels set magnetically using a knob (a magnet is moved near the rotating disk thereby increasing its rotating resistance). The distance from the pedal to the center is 0.165 m. At resistance level 4, if I put a weight greater than or equal to 0.750 kg on the pedal (such that the direction of the force is normal to the ground and tangent to the circle generated by the rotating pedal, that is when the pedal is at "hour 9 position"), then the system rotates. The system does not rotate if I use a lower weight. If I pedal at 65 rpm I should generate the following power in watts:

    P = 0.750 x 9.81 x 0.165 x 2 x Pi x 65 / 60 = 8.26 W

    Is the above calculation correct? It assumes the force applied by the legs is constant for the whole revolution (which is not actually the case but I hope it's a good approximation).

    Are there other assumptions I didn't consider? The reason I'm skeptical is that 8 W seems a very low number, considering that I'm using a resistance of 4 of 8.

    Even if I were pedaling at 120 rpm and level 8, the power (using the above formula) would only be 18.71 W.

    What am I missing?

  2. jcsd
  3. Jul 4, 2017 #2


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    Science Advisor

    Probably that the resistance at 65RPM doesn't equal the static resistance.
  4. Jul 4, 2017 #3
    Yep. Unfortunately I have no other information that can help me understanding how the force varies with speed.
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