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Thread: PI loops and feed forward

  1. PI loops and feed forward

    I am working on keeping my newfangled wheel encoders from making wild speed oscillations and was looking at some example code.

    Code:
    err_R = (req_speed_R - enc_speed_R);                 // calculate proportional term
    i_err_R = calc_vel_integ(i_err_R, err_R);            // calculate integral term, with saturation to prevent windup
    req_err_R = (req_speed_R * 8) / 10;                  // calculate velocity feed forward term
    out_R = calc_vel_out(req_err_R + err_R + i_err_R);   // calcuate motor outputs based on total error term
    I was reading about PI loops and have a good idea what the proportional and integral terms are. But I was reading about feed forward and was confused as to what role it is playing here.

    The full code is here:
    http://www.nubotics.com/support/ww01...c_square.c.php

    But I am really just not understanding what the feed forward part of this code is doing. Any help clarifying it for me would be appreciated.
    Last edited by Resilient; 03-25-2009 at 09:15 PM.

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