[From Bill Powers (2002.05.02.1448 MDT)]
Fred Nickols (2002.05.02.0645) --
Could you say some more about what you've just said or point me to the
relevant reading? More particularly, what is it you experience when
designing electronic systems? How does PCT explain it?
Last question first. We're talking here about particular things a human
system happens to become organized to do, not about anything fundamental.
My proposals about levels of organization are meant to include things like
performing rule-driven behaviors (the so-called "logic level"), but they
don't have anything to say about _which_ rules will be in effect. For that,
we simply have to observe what people do. PCT can't help us there.
We would use PCT to explain how it is that a rule can be put into effect,
not a particular rule but any rule. Briefly, I would suppose that we
perceive our actions and their effects as being examples of a rule, compare
the perceived rule with the rule we intend to be in effect, and if there is
a discrepancy,. alter the reference signals being sent to lower systems so
as to reduce the discrepancy. "Was the move I just made (or imagined) a
legal move in chess? " If not, retract it before letting go of the piece,
and try a different move.
Designing electronic systems and probably most other kinds is a juggling
act, in which one considers different components, materials, and
relationships among parts while controlling for many variables. For
example, in the robot design that Bruce and I are working on, we've
considered servo motors of many sizes, weights, torque
capacities, speeds, prices, degrees of durability, and frictional losses.
We've looked at at least three ways of simulating a muscle's internal
spring characteristics and viscous damping (which we've decided to emulate
electronically rathen than use literal dashpots). We've considered plastic
construction materials and model-maker's plywood. We've considered direct,
cable, and chain drives. We've looked at electronic interfaces and
breadboarding materials, and at pressure-sensitive rubber for detecting
forces. We've looked at the way many other people have designed their
hexapods, and indeed two such people have joined in the effort and are
contributing their own extensive experience in building walking models.
The process is one of trying to meet many criteria (reference levels) as
closely as possible and all at the same time, even though initially the
reference conditions are highly uncertain. A great deal of it takes place
in imagination, as we put mental models into action to see what problems
arise. Each of the criteria involves its own controlled variable, and
reference levels for each one that we would like the final model to match.
For example, Bruce just worked out that a particular design would be able
to support a total of a little over 2 kilograms of weight on its six legs.
Is that enough? If it turns out that all the stuff we want to load on the
body weighs more than that, the answer is no: We'd satisfy one set of
criteria but make it impossible to satisfy others, and that would be a
conflict. So we could, if necessary, consider putting less load on the body
or increasing the power of the motors, or maybe other things we haven't
thought of yet.
As far as I can see, no real decisions have been needed yet. Each possible
design leaves a certain amount of overall error, but nothing has progressed
far enough to call for a choice to be made. As the model takes a more
definite shape, certain things catch the eye -- for example, in one drawing
there is a servo motor mounted on the distal leg segment, whereas in
biological systems the motive power for that segment would come from
muscles in the proximal segment. We aren't explicitly trying to mimic any
biological system, but the thought is always there in the background -- a
goal of lesser priority, meaning we control for it with lower gain than for
the others.
In my own design efforts over the years, I've always felt more disorganized
than I thought other people were. I don't have a nice neat plan that leads
uniformly toward the final design. I get a sense of the system gradually
taking shape as a photographic print in the developer gradually begins to
show forms . Many variables change as the design progresses, gradually
converging toward one definite form rather than another, until in the end
all other possibilities have fallen away, leaving the finished product. I'm
controlling for a lot of variables, herding them toward goal states which
themselves change during the development. There are tensions among the
different control processes, and reducing or eliminating them is one of the
means of moving toward the final design.
Needless to say, I see a great deal of reorganization going on, at least in
the way I design systems. In engineering schools there is a strong tendency
to try to solve problems by looking up solutions already worked out, but I
always seem to see something to improve on, or do differenty anyhow, and
probably waste a lot of time reinventing wheelss
Different people are different, is what it comes down to. But the hierarchy
of perception and control follows the same principles in all of them, or so
I think.
Best,
Bill P.
···
Regards,
Fred Nickols
740.397.2363
nickols@safe-t.net
"Assistance at a Distance"
http://home.att.net/~nickols/articles.htm
) Again, the original problem is dropped and a new one(s) are