pololu motor shields

schufti Dec 10, 2020

  1. schufti

    schufti TrainBoard Member

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    triggered by a post lately, I had a look at the pololu motor shield(s) and the definition in MotorDrivers.h

    for my understanding the conversion factor for the pololu mc33926 is wrong.
    for standard arduino settings (5V reference, 10bit resolution) we have 5/1023 V = ~4.89mV/cnt
    according to the pololu mc33926 datasheet we get 525mV/1000mA = 0.525mV/mA
    thus giving 4.89/0.525 = 9.31 mA/cnt
    so if I interpret the "raw2mA()" correctly, the conversion factor should be 9.3 instead of 18

    concerning this "low resolution" it would make sense to switch to a lower reference (e.g. 1.1/2.56 internal, see https://www.arduino.cc/reference/en/language/functions/analog-io/analogreference/) for the pololu type of motor shields depending on used Arduino (2.56V only on Mega)

    But there are even worse pololu type shields! With e.g 140mV/A they would demand the 1.1V reference to get any relevant resolution.
     
  2. schufti

    schufti TrainBoard Member

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    with reference to the modified L298 (or else) boards, why do you recommend rediculously high ohm resistors leading to high loss/wattage instead of adding another parameter to a motorboard definition seting the adc reference voltage? (see posting above?)

    any reason why it wouldn't work?
     

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