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Homework Help: Output of Lead-compensator

  1. Feb 15, 2013 #1
    1. The problem statement, all variables and given/known data

    Hello, I'm not looking for an answer to my problem, just some hints. Any help would be greatly appreciated.
    I am required to control a hexacopter, so I'm designing a lead compensator to control the height, it should be able to counteract the pull of gravity. So far I have designed it, but my problem is that I need its output to be in PWM form.
    I already have a scaling which is a= 0.1956 N/PWM, it is also given that a value of 143 PWM will generate hover thrust.(These constants are found from tests on the motor, and are for all 6 motors).

    2. Relevant equations
    I realize that the feedfwd (see block diagram) should be some value, but I don't know what.

    3. The attempt at a solution

    Attached is a snapshot of the block diagram.

    Thanks for any help :)

    Attached Files:

  2. jcsd
  3. Feb 17, 2013 #2


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    I've long since forgotten my control theory but what does 143PWM mean? What are your units for PWM in a= 0.1956 N/PWM ?

    Is it a = 0.1956 Newtons/percent ?

    If the pulse width modulation can vary from 0% to 100% how can you have 143%
  4. Feb 17, 2013 #3
    That is actually a very good question, what I can see from the data that was given to me is that the transfer function for the motor was derived by subjecting it to steps from 150 PWM to 170 PWM, from there a linear regression could be made, and from there it is derived that the slope is a = 0.1956 Newton/PWM. Which means for every PWM sent in, 0.1956 Newton is added to the system.
  5. Feb 19, 2013 #4
    I just found out, that it's how the Arduino board works, you write 0-255, where 0 is 0% duty cycle, and 255 is 100 % duty cycle
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