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Motor combination to drive multiple tyres

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  1. Feb 14, 2018 #1
    If I need 50,000 Nm of torque to rotate a wheel, and I am rotating it about its rim (like the London eye), would 5 10,000 Nm motors each connected to a set of tyres to rotate it (the motors are not connected to each other), or would these motors first need to be connected to each other and then drive a set of tyres or would I need a single 50,000 Nm motor connected to a set of tyres?

    Thank you.
     
  2. jcsd
  3. Feb 14, 2018 #2

    BvU

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    Hello Jay, :welcome:

    The total torque is simply the net (vector) sum of the torques applied, so it isn't necessary to connect the motors or have only a single one.

    My first guess is that 10000 Nm is way too much to ask from a tyre, but you may have better info.

    Good luck with your design !
     
  4. Feb 14, 2018 #3
    The plan is to split the 10,000 between 4-5 tyres
     
  5. Feb 14, 2018 #4

    BvU

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    My reasoning: accelerating a 1000 kg car with 4 m/s2 requires 1000 N per tyre.
    With a radius of 0.25 m that is 250 Nm of torque per wheel
     
  6. Feb 14, 2018 #5
    I understand but our acceleration is tiny, the wheel runs at 1 revolution per 24.17 minutes and an acceleration time of around 3 minutes, giving an angular acceleration of something like 10^-5 if I remember right.
     
  7. Feb 14, 2018 #6

    BvU

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    But you said you needed 50000 Nm ?
     
  8. Feb 14, 2018 #7
    Yes we are going to have 5 10,000 Nm motors each connected to 4-5 tyres
     
  9. Feb 14, 2018 #8

    BvU

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    Still don't understand: your final angular velocity is ##\displaystyle{{2\pi\over 24.17 * 60 }\approx 0.0043} ## rad/s. If you reach that in 180 s, your angular acceleration is 2.4 10-5 rad/s2.

    With 50 kNm you could handle a moment of inertia of 2.1 109 kg##\cdot##m2 which I guess is not far from the London eye !?
     
  10. Feb 14, 2018 #9
    My mistake with the numbers i didn't have access to exact numbers of our project when writing this thread so I used approximations, here are my workings:

    The time to accelerate is 240 s
    The angular velocity is 0.00433 rad/s
    The inertia is 4.3*109
    Therefore the torque needed is 77500 Nm approx.

    This is spread over 8 motors so for simplicity let's say 10,000 Nm per motor, each motor will drive 4 x 0.5m radius tyres.
     
  11. Feb 14, 2018 #10

    BvU

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    Looked it up. With 1900 tonnes and 70 m radius London eye has ##I = ## 9.3 109 kg##\cdot##m2.

    Your thingy half that ##I## ? If so, I agree with your calculations. Still worry about 5000 N per tyre, but I suppose truck tyres manage it too.
     
  12. Feb 14, 2018 #11
    Yes we are planning on using big tyres, and our radius is 50m
     
  13. Feb 15, 2018 #12

    CWatters

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    Just a heads up...you can have problems with asymetric load sharing if you connect some types of motors in parallel.
     
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