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Calculation of torque power for BLDC

  1. Feb 14, 2013 #1
    i am building a solar electric bicycle for my final year project,in our project we are using solar panel to convert solar energy into electric energy and that energy will be stored in the battery.
    now we require brush-less DC motor to start the bicycle.
    so which torque equation should i use to calculate torque power and also how to decide the rating of the motor??
    we are using solar panel of 12 V and also battery of 12 V and also using DC-DC boast converter to step up the rating of 12 v to the volts which we require for the bicycle.
    so please help me out with this..
    but first of all i have to decide the torque power and torque rating of motor because based on motor rating only i can decide the rating of solar panel and battery.
    so please tell me how to calculate motor torque and also tell me the torque equation.
  2. jcsd
  3. Feb 15, 2013 #2
    Hello Treasure -- Welcome to PF.

    You may get some useful specs from a manufacturer like Bionx.

    Your DC/DC converter may need to be buck/boost to manage the power to the motor from 0 V up to the max. It may be worth while to have a battery V equal to the max Motor voltage. So the Motor control is ONLY a buck, for example: Solar -> Boost -> Battery -> Buck -> Motor.

    As for motor torque - I would back calculate, a good practical experiment, from pushing someone on the Bike, and measure the force needed. So start with Force and Wheel Radius....Torque - etc.
  4. Feb 15, 2013 #3
    Is it not time to use some of the knowledge you have gained from the years in college? Classical mechanics would go a long way, in fact all the way.

    What is torque and why do you need it? What is the relation to power? What speed are you aiming for? Which acceleration? What is the inertia of your system, what is the weight of the system? Do you need a reduction gear? Is the load torque constant or will it depend on speed and terrain?

    Or should you first consider the amount of power you can deliver from the battery and PV at a certain instant of time? I would be a poorly designed system if your power supply only can provide 500W and motor is rated 1000W.

    Show us a free body diagram, some equations and numbers...
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