[From Dag Forssell (940725 0800)] [Bill Leach 940724.14:31]
I tend to believe that I do "understand" the essential basics and
believe that was possible because as a child I encountered control
systems that I was free to play with (servo loop positioners).
Though I had not thought about it in years, I still remember my
initial surprises as I "fooled around" with these systems and
learned of their unique behaviour!
Bill, please tell me more.
Two years ago, Wayne Hershberger inspired me to explore model
airplane servos, and I made up a hand held demonstration unit.
Gary Cziko did the same with more "off-the-shelf" gear. I read into
your description some capability to show much more than mere
"dial the reference" in one place and watching the servo perform
in another. I did include an ampmeter in the circuit, so one can
watch the "effort" put forth when disturbances are applied.
What technology are you talking about? Is it different from what
I described? What unique behavior did you mean?
Best, Dag
<[Bill Leach 940725.21:17 EST(EDT)]
[Dag Forssell (940725 0800)]
No, there was no "more". These were surplus military servo amplifier
(vacuum tube) and selsyn motor control units with a gear train and
mechanical arm. They were some sort of "linear positioner". They were
not particularly fast (only because of the gear train) but they were
rather strong, even with the addition of some additional current limiting
in the final stage anode supply line.
It is just that the control system was among the many amazing phenomenon
that my neighbor introduced me to while I was still rather young. I
remember "experiencing" the idea that "this thing wanted to maintain the
reference position against whatever tried to force it out of position."
Since Fred had modified the circuit a bit, I was able to play around with
the "effects" of reduced gain (switch in a variable negative feedback
circuit within the amplifier itself), actually feel the effects of the
protection circuit (a concept that we typically call "foldback" but was
described by Bill P. when he discussed the possible error signal strength
variations as a function of difference magnitude between reference and
perception to show how some perceptual control errors might not
necessarily create undue stress. That is, error magnitude first quickly
rises to a peak value with very small reference/perception difference but
rapidly drops to some low value if the difference becomes larger -- I
believe that the reference for Ice Cream was used for the example).
What unique behaviour did you mean?
To a young child such as I was at the time, experiencing a "simple"
electro-mechanical system that "controlled" was pretty unique.
Is it different from what I described?
No, I don't think it was essentially different other than it would not be
considered to have been "hand held" by anyone weaker than a Rosy Greer!
-bill