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Sizing a dc motor

  1. Sep 10, 2009 #1
    I recently started doing research to build one of these (popular?) two-wheeled balancing things. (A segway clone)
    I don't know how to calculate the proper size motors (a pair of motors) for this. I know you have to consider the torque and rotational speed required to size the motor.

    Desired rotational speed is easy, I just take a desired speed and a wheel size and figure out how fast it needs to rotate to reach that speed.

    I'm not sure how to calculate torque requirements.
  2. jcsd
  3. Sep 11, 2009 #2
    Here are some motors I am comparing. The difference here is price (and obviously additional hardware on the more expensive one)

    There is the CIM motor, according to the specs:
    Torque, speed, current, power, efficiency
    0, 5310, 2.7, 0, 0 (free)
    64, 4320, 27, 205, 63 (normal)
    45, 4614, 19.8, 154, 65 (max efficiency)
    171.7, 2655, 67.9, 337, 41 (max power)
    343.4, 0, 133.0, 0, 0 (stall)

    Here is a midwestMotion products motor: (it is the expensive one)
    http://www.midwestmotion.com/products/brushed/12VOLT/12%20VOLT,%20250-324%20RPM%20GEARMOTORS/12%20VOLT,%2040-149%20IN-LBS/ENCODER%20-%20BRAKE%20COMPATIBLE/MMP%20S28-150E4-12V%20GP81-014%20TECH%20SPECS.pdf [Broken]
    Torque, speed, current, power, efficiency
    0, 4140, 1.7, 0, 0 (no load)
    110, 3640, 28.2, 296, N/A (rated continuous)

    The more expensive motor has more torque from what I read on the datasheets. It is 3.2" diameter vs 2.5" on the CIM motor. What other big differences am I missing here (I put up links to the spec sheets of each motor)?
    Last edited by a moderator: May 4, 2017
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