Javi, One minor clarification as follows:
On Wed, Jan 28, 2015 at 05:00:35PM +0000, Javi Merino wrote: <big cut> > + > +k_d > +--- > + > +`k_d` configures the PID loop's derivative term constant. It's > +recommended to leave it as the default: 0. > + I know we are considering K_d = 0. However, ... <yet another big cut> > + /* > + * Calculate the derivative term > + * > + * We do err - prev_err, so with a positive k_d, a decreasing > + * error (i.e. driving closer to the line) results in less > + * power being applied, slowing down the controller) > + */ > + d = mul_frac(tz->tzp->k_d, err - params->prev_err); ... Shouldn't the above d component consider the rate of changes over time of the error? I would expect you should do: d = k_d * (dE / dt) or d = K_d * ((err - params->prev_err) / sampling_period) in plain C: + d = mul_frac(tz->tzp->k_d, err - params->prev_err); + d /= tz->passive_polling; /* might require fixed point division */ --- Eduardo Valentin
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