On Mon, 28 Dec 1998, John Payson wrote:

> Is the preference for PID systems primarily a result of inertia, or
> is there some other benefit that PID-modeled systems have over more
> application-modeled ones?

PID servos can be designed in about 10 minutes using one of scores of
specialized code generators (which I've never used), and are, in general,
considered to be THE ground Rhino horn potion.

In reality, even a poor backlashing gear train in a model servo (between
the motor and the position pot) will ruin any chance of a good PID
approach to do its job, especially at inversion points and at small
deflections. A pure PID matched to a slow, heavy load used with a
backlashing gear train will oscillate when idle with almost 100%
probability, at least when settling.

There are also several people who sell newsletters on PID for $10 (?) in
newsgroups, same for Fuzzy logic. If someone is surfing in search for a
servo solution, he will pick either PID or Fuzzy and drop Fuzzy because it
is more complex. This leaves him with PID although he may actually need PD
or PI in reality (A PID with a zero in the resp. coefficient will do that
however, and the code generators sold, do that quietly, or so I am told).
So PID it is.

Peter