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Lab 2a and Lab 5c: Should remove attachment from the shaft?

Yu Zou
Expert 1190 points

Hello,

In lab5c, to ID the inertia, we attach the system to the motor, but free of load. (Ex: attach drum but no clothes, no water, in washing machine). Then, I'm wondering, to ID the motor parameters, is the lab2a should be same case?? Or, we should remove all the attachment from the shaft, leaving the motor itself alone??

  • 0
    TI__Guru** 119680 points

    For motor parameter ID it is best to have 0 coupling and 0 load. This is mostly for stability reasons as during ID you are start open loop and slowly close the loops based on the calculations. For inertia and friction ID you want 0 load, but you must have the typical coupling of the system as that is what you would like a baseline for. SpinTAC controller is still stable even if the system inertia changes by up to 8x, but you get best performance when your ID value matches actual.

  • 0 in reply to ChrisClearman
    Expert 1190 points

    Very clear!

    Before verifying your answer, I also wonder the ADC offset ID (Lab3a) - it basically has nothing to do with what motor I'm using, right? It is purely about the drv driver itself, right? Thus, I don't need to repeat this part for different motors, as long as I'm using the same drv.

  • 0 in reply to Yu Zou
    TI__Guru** 119680 points

    Correct, the voltage and current offsets are for your hardware pairing only. 

    You can use the saved values in user.h

    In practicality, for a product you won't have this offset available and wouldn't be able to compile for each HW set though. So your option is to use the OffsetCalc each time you power cycle the product, or do a board test and store your offsets in OTP or off chip EEPROM, etc.

    You ca also use the OffsetCalc as a diagnostic check, checking over time if it drifts from baseline by certain % over time to notify of any HW issues.