DIY control systems

[From Adam Matic 2014.01.10 2110 CET]

Hi all,

Here are the instructions and parts list for building a velocity control system using an Arduino board. Included is the code for the Arduino, and the code for a Processing application that monitors and displays variables from the control system. This is the first version of a first article in a series, hopefully. I’ll go over it a few more times and then probably start a blog or something like that. I’m not sure yet.

Feel free to comment or suggest anything either on this thread or to my email. I’ll be happy to answer any questions.

Adam

A simple control system.doc (216 KB)

SimpleCS.pde (2.9 KB)

simplecs.ino (1.77 KB)

Thanks for posting this, Adam. It looks really interesting!

Kent

[From Adam Matic 2014.01.10 2110 CET]

Hi all,

Here are the instructions and parts list for building a velocity control system using an Arduino board. Included is the code for the Arduino, and the code for a Processing application that monitors and displays variables from the control system. This is the
first version of a first article in a series, hopefully. I’ll go over it a few more times and then probably start a blog or something like that. I’m not sure yet.

A simple control system.doc (216 KB)

SimpleCS.pde (2.9 KB)

simplecs.ino (1.77 KB)

···

On Jan 10, 2014, at 2:10 PM, Adam Matic wrote:

Feel free to comment or suggest anything either on this thread or to my email. I’ll be happy to answer any questions.

Adam

[From Adam Matic 2014.01.10 2230 CET]

Bruce Abbott (2013.12.27.1225 EST)

Have you seen Rupurt Young’s implementation of the inverted pendulum? (See, e.g., <http://www.youtube.com/watch?v=fDz2SbS8nmo&feature=youtu.be&gt;http://www.youtube.com/watch?v=fDz2SbS8nmo&feature=youtu.be .

AM: Sorry, somehow I didn't notice this post. Yes, I've seen Rupert's inverted pendulum and Rupert has kindly sent me a lot of his code. I hope to make something similar sometime in the following months.
I didn't know about your arm demo. I'm interested - did you have to read out servo's potentiometer values to calculate angles on the joints?
I'd love to see a presentation or a paper about it if you could send it.
Also, have you shown the mulit-level control structure to a roboticist?
Adam

[From Adam Matic 2014.01.10.2255 CET]

···

On Fri, Jan 10, 2014 at 10:07 PM, McClelland, Kent MCCLEL@grinnell.edu wrote:

Thanks for posting this, Adam. It looks really interesting!

Kent

AM:

Thank you. I hope the more complex ones will be even more interesting. A single loop control system could be used for demonstrating core principles like what is control, what are disturbances, and so on. An arm, an inverted pendulum, or, as Matti posted, an x-y positioning system could be used for demonstrating multi-level control or reorganization.

It seems to me, if we could make gadgets that do fun or impressive things, people will come and ask, oh, how does that work, and oh what is the theory behind it.

The great thing about 2014 is that there are all these new electronic boards, sensors and effectors, significantly more affordable, more easy to use and program then just a few years before. There is the whole ‘maker’ movement, 3D printers, open-source visual data processing software… And then there are DARPA challenges, in which robots seem to be built on the same principles as 50 or 60 years ago, just with more computing power, Richard Kennaway posted a link a few weeks ago.

I’m quite enthusiastic about all this.

Adam

[From Kent McClelland 2014.01.10.1627 CST]

Adam Matic 2014.01.10.2255 CET

KM: I remember suggesting on CSG net 20 years ago or more that if we wanted to get more attention for PCT somebody should be building computer games or robots based on PCT circuits. I didn’t have the technical chops or time to do it myself. Sadly, I still
don’t.

I’m delighted to see someone taking up the challenge with all the new stuff now available. It would be great if I could figure out a way by the time I teach a PCT course again, probably spring a year from now, to get some gadgets like this for my university
students to play with. Keep up the good work.

Best,

Kent

···

On Fri, Jan 10, 2014 at 10:07 PM, McClelland, Kent
MCCLEL@grinnell.edu wrote:

Thanks for posting this, Adam. It looks really interesting!

Kent

AM:

Thank you. I hope the more complex ones will be even more interesting. A single loop control system could be used for demonstrating core principles like what is control, what are disturbances, and so on. An arm, an inverted pendulum, or, as Matti posted,
an x-y positioning system could be used for demonstrating multi-level control or reorganization.

It seems to me, if we could make gadgets that do fun or impressive things, people will come and ask, oh, how does that work, and oh what is the theory behind it.

The great thing about 2014 is that there are all these new electronic boards, sensors and effectors, significantly more affordable, more easy to use and program then just a few years before. There is the whole ‘maker’ movement, 3D printers, open-source
visual data processing software… And then there are DARPA challenges, in which robots seem to be built on the same principles as 50 or 60 years ago, just with more computing power, Richard Kennaway posted a link a few weeks ago.

I’m quite enthusiastic about all this.

Adam

[From Bruce Abbott (2014.01.10.11810 EST)]

Adam Matic 2014.01.10 2110 CET –

AM: Here are the instructions and parts list for building a velocity control system using an Arduino board. Included is the code for the Arduino, and the code for a Processing application that monitors and displays variables from the control system. This is the first version of a first article in a series, hopefully. I’ll go over it a few more times and then probably start a blog or something like that. I’m not sure yet.

AM: Feel free to comment or suggest anything either on this thread or to my email. I’ll be happy to answer any questions.

BA: Very nice, Adam, I’m looking forward to seeing more of your work along these lines!

Adam Matic 2014.01.10 2230 CET–

Bruce Abbott (2013.12.27.1225 EST

BA: Have you seen Rupurt Young’s implementation of the inverted pendulum? (See, e.g., http://www.youtube.com/watch?v=fDz2SbS8nmo&feature=youtu.be .

AM: Sorry, somehow I didn’t notice this post. Yes, I’ve seen Rupert’s inverted pendulum and Rupert has kindly sent me a lot of his code. I hope to make something similar sometime in the following months.

AM: I didn’t know about your arm demo. I’m interested - did you have to read out servo’s potentiometer values to calculate angles on the joints? I’d love to see a presentation or a paper about it if you could send it.

Here’s a photo I took a few minutes ago of the device:

image00224.jpg

As you can see, there’s not much to it: two RC servos, an sscII pulse-width modulation board (seetron.com) to send signals to the two servos and an OOPic II microcomputer board (Savage Innovations). The sscII includes a serial interface to connect to a PC’s serial port. (Shown is the cable for making that connection.) I also programmed the OOpic II shown below the arm to run the demo on its own, without the PC. In that case two potentiometers were connected to the OOPic board to provide the position reference signals.

A Delphi program running on the PC displayed a facsimile of the arm, and by moving two sliders via the mouse, you could change the angles of the two joints.

The RC servos contain their own pots to determine the position of the servo’s output shaft, but these are not accessible to the program. Instead, the program simply sent pulse-width modulated reference signals to the servos; the computer display showed the reference positions of the arm rather than sensed positions, but the servos are high gain control systems, so there wouldn’t be a noticeable difference between r and p unless the load on the servos was severe.

There aren’t many (if any) computers available now that have a serial port; not long after I purchased these devices the USB port became popular and now such things usually interface to the USB port. Also, as you noted, the cost of these things has decreased quite a bit. I had a few hundred U.S. dollars invested in what you see here.

My presentation at the CSG conference was rather informal and I did not write it up in a paper. There may be a video record of it, however. One of the conference participants, Shelley Roy, told me later that the demonstration, simple as it was, really helped cement her understanding of the control process.

Also, have you shown the mulit-level control structure to a roboticist?

No, I haven’t.

Bruce

[From Adam Matic 2014.01.10. 1430 CET]

···

KM: I remember suggesting on CSG net 20 years ago or more that if we wanted to get more attention for PCT somebody should be building computer games or robots based on PCT circuits.

AM:

I agree. And it works the other way around too - if someone would use PCT in building computer games and robots, he would have a big advantage over current games and robots. For example - algorithms that calculate limb positions for game characters are terribly complex and computationally expensive. Whole companies are dedicated to making these algorithms produce more fluid and natural looking movements. Notable example: http://www.naturalmotion.com/middleware/euphoria/

A PCT based ‘neural net’ would would probably work much faster and improve gameplay, but there is still a lot of work to be done to create a net that does whole body movement. Fortunately, there are great physics and ragdoll simulation environments today that can make the job easier, and they are getting more and more user friendly.

I remember playing a game called Bug Brain a few years ago. http://www.biologic.com.au/bugbrain/ . Brilliant concept for a game, but based on a digital neuron model. You get a bug and a little world in which it can move, and you need to connect neurons to create a brain that moves the bug toward food or light. Something like this could be not only a game, but a real research platform. You get a ‘world’. You choose a few sensors and effectors for an organism. And then you get a ‘brain design’ section in which you connect inputs, outputs and references to form any kind of a control system you can imagine. Or just set it to reorganize and evolve.

KM: I’m delighted to see someone taking up the challenge with all the new stuff now available. It would be great if I could figure out a way by the time I teach a PCT course again, probably spring a year from now, to get some gadgets like this for my university
students to play with. Keep up the good work.

AM: Thanks, I hope to have a small selection of gadgets and instructions on how to make them by this time next year.

Adam

AM: Thanks for the explanation!
Adam

···

On Sat, Jan 11, 2014 at 12:10 AM, Bruce Abbott <<mailto:bbabbott@frontier.com>bbabbott@frontier.com> wrote:

BA: As you can see, there’s not much to it: two RC servos, an sscII pulse-width modulation board (<http://seetron.com>seetron.com) to send signals to the two servos and an OOPic II microcomputer board (Savage Innovations). The sscII includes a serial interface to connect to a PC’s serial port. (Shown is the cable for making that connection.) I also programmed the OOpic II shown below the arm to run the demo on its own, without the PC. In that case two potentiometers were connected to the OOPic board to provide the position reference signals.

A Delphi program running on the PC displayed a facsimile of the arm, and by moving two sliders via the mouse, you could change the angles of the two joints.

The RC servos contain their own pots to determine the position of the servo’s output shaft, but these are not accessible to the program. Instead, the program simply sent pulse-width modulated reference signals to the servos; the computer display showed the reference positions of the arm rather than sensed positions, but the servos are high gain control systems, so there wouldn’t be a noticeable difference between r and p unless the load on the servos was severe.

Hi friends,

I was wondering if there is any interest among CSGnet-ers in making electronic control systems.

I’ve been playing with those for more than a year, turns out it’s quite simple to make a control system with just basic electronic boards, sensors and motors. I like the idea of going trough LCSIII, and I think it might be a nice complement to make simple electronic control systems to see in “real life” what happens when some parameters are changed and what happens when some others are changed.

We could start with simple ones and use them as demonstrations of core PCT principles, then move on to more complex ones. For the ‘live block’ from LCSIII, we can make a motor velocity control system, for a two-level system a servo motor, and for a multi-level system an arm-like structure.

I’ll start a blog and post build instructions, hopefully in two or three weeks, after the holidays.

Oh, and Merry Christmas and happy holidays from Croatia, everyone!

Best,

Adam

[From Rick Marken (2013.12.25.0940)]

···

On Wed, Dec 25, 2013 at 4:18 AM, Adam Matic adam.matic@gmail.com wrote:

Hi friends,

I was wondering if there is any interest among CSGnet-ers in making electronic control systems.

I’ve been playing with those for more than a year, turns out it’s quite simple to make a control system with just basic electronic boards, sensors and motors. I like the idea of going trough LCSIII, and I think it might be a nice complement to make simple electronic control systems to see in “real life” what happens when some parameters are changed and what happens when some others are changed.

We could start with simple ones and use them as demonstrations of core PCT principles, then move on to more complex ones. For the ‘live block’ from LCSIII, we can make a motor velocity control system, for a two-level system a servo motor, and for a multi-level system an arm-like structure.

I’ll start a blog and post build instructions, hopefully in two or three weeks, after the holidays.

RM: Sounds great Adam! Send the address of the blog as soon as you get it going!

Best

Rick

Oh, and Merry Christmas and happy holidays from Croatia, everyone!

Best,

Adam


Richard S. Marken PhD
www.mindreadings.com
The only thing that will redeem mankind is cooperation.

                                               -- Bertrand Russell

[From Matti Kolu (2013.12.27.0530 CET)]

Adam Matic--

I like the idea of going trough LCSIII, and I think it might be
a nice complement to make simple electronic control systems to see in "real
life" what happens when some parameters are changed and what happens when
some others are changed.

Yes. You might have already read this post, but here's Powers about
his experiences teaching PCT with the help of live demonstrations.
("Retrofaction" should be read as "control".)

Bill Powers (960130.0730 MST)--
[...]

···

------------------------------------------
In 1972 and 1973, I gave a series of student-sponsored seminars, backed
by Hugh Petrie, Don Campbell, and (for anthropoplogy students), P. J.
Bonhannan at Northwestern University. One of the things I did to give
the students the feel of a retrofactive system was to bring an x-y
recorder to the sessions, so the students could physically interact with
it. This was not the modern type in which a stepper motor generates the
pen positions, but the old-fashioned analog type in which DC servomotors
moved the pen carriage in x and y, and the position was sensed by a
linear slidewire potentiometer along each axis.

The first lesson consisted simply of taking the pen carriage between
thumb and forefinger and trying to move it. Until he or she actually
tried this, it was clear that each student had understood my
introductory descriptions of negative feedback systems in some way that
was off the mark. I could tell, because every one of them, on grasping
the pen carriage and trying to move it, looked startled or surprised --
even after having just seen another student doing the same thing. What
surprised them the most was that the carriage _resisted_ them,
energetically enough that they could hardly feel (or see) any motion of
the carriage at all. With enough applied force, the carriage would seem
to break loose and move without any further increase in resistance, as
if it had come out of a detent, but always pushing back toward the
original position. The motor had a slip-clutch on it to prevent damage,
and when enough force was applied to the carriage, the motor could be
heard to hum louder and louder and then start spinning at high speed.
The experience was one of being resisted by a very active system. All of
the students said that it "felt alive."

The next demonstration was to have each student take hold of the x or y
offset control and turn it. This control actually varied the reference
signal for the retrofactive system that positioned the carriage. Again
the students were surprised, because there was no perceptible lag
between the turning of the knob and the movement of the carriage, unless
a real effort was made to turn the knob by a large amount in as little
time as possible. And then the lag was less than a quarter of a second
from the initial position to the final position. One student
hypothesized that there was a direct mechanical connection between the
knob and the carriage, and refused to believe that no such connection
existed until I took the control panel off and showed him the
potentiometer and the wiring, and operated the knob.

The next demonstration consisted of having one student turn the
reference-signal knob while another (or the same) student tried to move
the carriage by pushing on it. This quickly got across the idea that the
reference signal _determined_ the pen position, with influences from
disturbances having no perceptible effect until the disturbance exceeded
the ability of the servo motors to resist it. So a feeble electrical
signal could swiftly and precisely move the pen carriage, while the
hidden retrofactive system prevented gross mechanical disturbances from
having any important effect.

For the final demonstration, I mounted four temperature-sensitive
thermistors and two photoelectric cells (looking in different
directions) on the pen carriage. I wired the outputs of these sensors
to the x and y reference signal inputs. There was no attempt to create
any sensible retrofactive systems; I just wanted to create some sort of
higher-level systems that worked through the reference inputs of the
lower-level retrofactive system.

This was a big hit. If you held a hand near a thermistor, the heat would
alter the pen position reference signals and the pen would move, either
toward or away from the hand. At the same time, light falling on the
photocells would contribute to the motions, so the shadow of the hand
also had a large effect. The whole system would very rapidly seek
positions where the balances of heat and light came into equilibrium
with the carriage position. Both heat and light disturbances, such as
from a cigarette lighter, would seem to make the carriage move in
strange ways to new positions, sometimes slowly and sometimes very
rapidly. If approached from the right direction, the thermistors would
do nothing until actual contact was made, and then jerk suddenly away
from the finger, or into it and beyond it (the thermistors were sticking
up on the ends of flexible wires). All kinds of purposive
interpretations could be offered: the carriage was trying to keep the
finger between itself and the window, the touch caused a startle
response, the carriage was chasing the finger or fleeing from it, and so
forth. But the students, having seen how each part of the system worked
and having gained a personal intuition of the system through physical
interaction with it, quickly arrived on their own at the _correct_
purposive interpretation: that the system was controlling some function
of heat and light sensor signals. Of course now they would all have to
be told that the system was retrofacting light and sensor signals, since
if they said "control" some people would interpret this to mean "react"
or "affect" or "influence" or "determine" or "cause." The students knew
that what they had experienced was none of these. What they had been
experiencing had never been mentioned in any of their psychology or
philosophy courses.
------------------------------------------------
I still try to teach through demonstration, but it's hard to get people
on the internet to explore the simple demos to get the kind of
understanding my students eventually got. Everyone wants to go on to
more interesting topics, big complicated systems doing big dramatic
things, and generally doing things that are deliberately made so complex
that they can't be done well, or be understood in any clear way. It's
almost as if people want to avoid the simple issues, the clear
phenomena, the explanations that either fit or don't fit with no
quibbling. As long as we flounder around with complex behaviors, any
theory about them can seem right -- who can prove they're wrong?

Bill Leach at one time was considering building some real
servomechanisms to use as demonstrations of real retrofactive systems
that people could physically interact with. I hope, Bill, that when your
current situation comes to some sort of even keel you can get back to
this project. Even if they cost $500 apiece, they would be worth it in
educational power. People who are serious about wanting to learn and
teach retrofaction theory would willingly pay the price to buy or rent
such devices.
----------------------------------------------------------------------

----
Matti

[From Rick Marken (2013.12.27.0900)]

···

Matti Kolu (2013.12.27.0530 CET)–

Yes. You might have already read this post, but here’s Powers about

his experiences teaching PCT with the help of live demonstrations.

(“Retrofaction” should be read as “control”.)

RM: Wonderful Matti. Thanks for posting it. I needed that!

Best

Rick

Bill Powers (960130.0730 MST)–

[…]


In 1972 and 1973, I gave a series of student-sponsored seminars, backed

by Hugh Petrie, Don Campbell, and (for anthropoplogy students), P. J.

Bonhannan at Northwestern University. One of the things I did to give

the students the feel of a retrofactive system was to bring an x-y

recorder to the sessions, so the students could physically interact with

it. This was not the modern type in which a stepper motor generates the

pen positions, but the old-fashioned analog type in which DC servomotors

moved the pen carriage in x and y, and the position was sensed by a

linear slidewire potentiometer along each axis.

The first lesson consisted simply of taking the pen carriage between

thumb and forefinger and trying to move it. Until he or she actually

tried this, it was clear that each student had understood my

introductory descriptions of negative feedback systems in some way that

was off the mark. I could tell, because every one of them, on grasping

the pen carriage and trying to move it, looked startled or surprised –

even after having just seen another student doing the same thing. What

surprised them the most was that the carriage resisted them,

energetically enough that they could hardly feel (or see) any motion of

the carriage at all. With enough applied force, the carriage would seem

to break loose and move without any further increase in resistance, as

if it had come out of a detent, but always pushing back toward the

original position. The motor had a slip-clutch on it to prevent damage,

and when enough force was applied to the carriage, the motor could be

heard to hum louder and louder and then start spinning at high speed.

The experience was one of being resisted by a very active system. All of

the students said that it “felt alive.”

The next demonstration was to have each student take hold of the x or y

offset control and turn it. This control actually varied the reference

signal for the retrofactive system that positioned the carriage. Again

the students were surprised, because there was no perceptible lag

between the turning of the knob and the movement of the carriage, unless

a real effort was made to turn the knob by a large amount in as little

time as possible. And then the lag was less than a quarter of a second

from the initial position to the final position. One student

hypothesized that there was a direct mechanical connection between the

knob and the carriage, and refused to believe that no such connection

existed until I took the control panel off and showed him the

potentiometer and the wiring, and operated the knob.

The next demonstration consisted of having one student turn the

reference-signal knob while another (or the same) student tried to move

the carriage by pushing on it. This quickly got across the idea that the

reference signal determined the pen position, with influences from

disturbances having no perceptible effect until the disturbance exceeded

the ability of the servo motors to resist it. So a feeble electrical

signal could swiftly and precisely move the pen carriage, while the

hidden retrofactive system prevented gross mechanical disturbances from

having any important effect.

For the final demonstration, I mounted four temperature-sensitive

thermistors and two photoelectric cells (looking in different

directions) on the pen carriage. I wired the outputs of these sensors

to the x and y reference signal inputs. There was no attempt to create

any sensible retrofactive systems; I just wanted to create some sort of

higher-level systems that worked through the reference inputs of the

lower-level retrofactive system.

This was a big hit. If you held a hand near a thermistor, the heat would

alter the pen position reference signals and the pen would move, either

toward or away from the hand. At the same time, light falling on the

photocells would contribute to the motions, so the shadow of the hand

also had a large effect. The whole system would very rapidly seek

positions where the balances of heat and light came into equilibrium

with the carriage position. Both heat and light disturbances, such as

from a cigarette lighter, would seem to make the carriage move in

strange ways to new positions, sometimes slowly and sometimes very

rapidly. If approached from the right direction, the thermistors would

do nothing until actual contact was made, and then jerk suddenly away

from the finger, or into it and beyond it (the thermistors were sticking

up on the ends of flexible wires). All kinds of purposive

interpretations could be offered: the carriage was trying to keep the

finger between itself and the window, the touch caused a startle

response, the carriage was chasing the finger or fleeing from it, and so

forth. But the students, having seen how each part of the system worked

and having gained a personal intuition of the system through physical

interaction with it, quickly arrived on their own at the correct

purposive interpretation: that the system was controlling some function

of heat and light sensor signals. Of course now they would all have to

be told that the system was retrofacting light and sensor signals, since

if they said “control” some people would interpret this to mean “react”

or “affect” or “influence” or “determine” or “cause.” The students knew

that what they had experienced was none of these. What they had been

experiencing had never been mentioned in any of their psychology or

philosophy courses.


I still try to teach through demonstration, but it’s hard to get people

on the internet to explore the simple demos to get the kind of

understanding my students eventually got. Everyone wants to go on to

more interesting topics, big complicated systems doing big dramatic

things, and generally doing things that are deliberately made so complex

that they can’t be done well, or be understood in any clear way. It’s

almost as if people want to avoid the simple issues, the clear

phenomena, the explanations that either fit or don’t fit with no

quibbling. As long as we flounder around with complex behaviors, any

theory about them can seem right – who can prove they’re wrong?

Bill Leach at one time was considering building some real

servomechanisms to use as demonstrations of real retrofactive systems

that people could physically interact with. I hope, Bill, that when your

current situation comes to some sort of even keel you can get back to

this project. Even if they cost $500 apiece, they would be worth it in

educational power. People who are serious about wanting to learn and

teach retrofaction theory would willingly pay the price to buy or rent

such devices.



Matti


Richard S. Marken PhD
www.mindreadings.com
The only thing that will redeem mankind is cooperation.

                                               -- Bertrand Russell

[From Bruce Abbott (2013.12.27.1225 EST)]

Much appreciated, Adam! I look forward to your contributions.

Have you seen Rupurt Young’s implementation of the inverted pendulum? (See, e.g., http://www.youtube.com/watch?v=fDz2SbS8nmo&feature=youtu.be .

Bruce

···

From: Control Systems Group Network (CSGnet) [mailto:CSGNET@LISTSERV.ILLINOIS.EDU] On Behalf Of Adam Matic
Sent: Wednesday, December 25, 2013 7:19 AM
To: CSGNET@LISTSERV.ILLINOIS.EDU
Subject: DIY control systems

Hi friends,

I was wondering if there is any interest among CSGnet-ers in making electronic control systems.

I’ve been playing with those for more than a year, turns out it’s quite simple to make a control system with just basic electronic boards, sensors and motors. I like the idea of going trough LCSIII, and I think it might be a nice complement to make simple electronic control systems to see in “real life” what happens when some parameters are changed and what happens when some others are changed.

We could start with simple ones and use them as demonstrations of core PCT principles, then move on to more complex ones. For the ‘live block’ from LCSIII, we can make a motor velocity control system, for a two-level system a servo motor, and for a multi-level system an arm-like structure.

I’ll start a blog and post build instructions, hopefully in two or three weeks, after the holidays.

Oh, and Merry Christmas and happy holidays from Croatia, everyone!

Best,

Adam


No virus found in this message.
Checked by AVG - www.avg.com
Version: 2014.0.4259 / Virus Database: 3658/6946 - Release Date: 12/24/13

[From Bruce Abbott (2013.12.27.1235 EST)]

Thanks for posting that, Matti! Some of those attending the CSG conference
a few years ago near Chapel Hill, NC may remember the "arm" demo I showed
off there. It consisted of two "rc" style servo motors acting as a shoulder
and elbow joint of a plywood arm. The servos were connected to a PIC
microcomputer which in turn could be connected via an RS232 serial port to a
computer. I had a program running on the computer that showed a graphic
representation of the arm and "slider" controls that could be manipulated
via mouse to change the reference angular positions of the servos. The arm
segments vigorously resisted attempts to manually rotate their joints (when
the control systems were active), but responded almost effortlessly to
changes in reference values. It was interesting to see the simulated arm on
the screen and the physical one on the table doing the same things in
response to manipulations of the references, confirming that our computer
model accurately simulated the real thing.

Bruce

···

-----Original Message-----
From: Control Systems Group Network (CSGnet)
[mailto:CSGNET@LISTSERV.ILLINOIS.EDU] On Behalf Of Matti Kolu
Sent: Thursday, December 26, 2013 11:29 PM
To: CSGNET@LISTSERV.ILLINOIS.EDU
Subject: Re: DIY control systems

[From Matti Kolu (2013.12.27.0530 CET)]

Adam Matic--

I like the idea of going trough LCSIII, and I think it might be a nice
complement to make simple electronic control systems to see in "real
life" what happens when some parameters are changed and what happens
when some others are changed.

Yes. You might have already read this post, but here's Powers about his
experiences teaching PCT with the help of live demonstrations.
("Retrofaction" should be read as "control".)

Bill Powers (960130.0730 MST)--
[...]
------------------------------------------
In 1972 and 1973, I gave a series of student-sponsored seminars, backed by
Hugh Petrie, Don Campbell, and (for anthropoplogy students), P. J.
Bonhannan at Northwestern University. One of the things I did to give the
students the feel of a retrofactive system was to bring an x-y recorder to
the sessions, so the students could physically interact with it. This was
not the modern type in which a stepper motor generates the pen positions,
but the old-fashioned analog type in which DC servomotors moved the pen
carriage in x and y, and the position was sensed by a linear slidewire
potentiometer along each axis.

The first lesson consisted simply of taking the pen carriage between thumb
and forefinger and trying to move it. Until he or she actually tried this,
it was clear that each student had understood my introductory descriptions
of negative feedback systems in some way that was off the mark. I could
tell, because every one of them, on grasping the pen carriage and trying to
move it, looked startled or surprised -- even after having just seen
another student doing the same thing. What surprised them the most was that
the carriage _resisted_ them, energetically enough that they could hardly
feel (or see) any motion of the carriage at all. With enough applied force,
the carriage would seem to break loose and move without any further
increase in resistance, as if it had come out of a detent, but always
pushing back toward the original position. The motor had a slip-clutch on
it to prevent damage, and when enough force was applied to the carriage,
the motor could be heard to hum louder and louder and then start spinning
at high speed.
The experience was one of being resisted by a very active system. All of
the students said that it "felt alive."

The next demonstration was to have each student take hold of the x or y
offset control and turn it. This control actually varied the reference
signal for the retrofactive system that positioned the carriage. Again the
students were surprised, because there was no perceptible lag between the
turning of the knob and the movement of the carriage, unless a real effort
was made to turn the knob by a large amount in as little time as possible.
And then the lag was less than a quarter of a second from the initial
position to the final position. One student hypothesized that there was a
direct mechanical connection between the knob and the carriage, and refused
to believe that no such connection existed until I took the control panel
off and showed him the potentiometer and the wiring, and operated the knob.

The next demonstration consisted of having one student turn the
reference-signal knob while another (or the same) student tried to move the
carriage by pushing on it. This quickly got across the idea that the
reference signal _determined_ the pen position, with influences from
disturbances having no perceptible effect until the disturbance exceeded
the ability of the servo motors to resist it. So a feeble electrical signal
could swiftly and precisely move the pen carriage, while the hidden
retrofactive system prevented gross mechanical disturbances from having any
important effect.

For the final demonstration, I mounted four temperature-sensitive
thermistors and two photoelectric cells (looking in different
directions) on the pen carriage. I wired the outputs of these sensors to
the x and y reference signal inputs. There was no attempt to create any
sensible retrofactive systems; I just wanted to create some sort of
higher-level systems that worked through the reference inputs of the
lower-level retrofactive system.

This was a big hit. If you held a hand near a thermistor, the heat would
alter the pen position reference signals and the pen would move, either
toward or away from the hand. At the same time, light falling on the
photocells would contribute to the motions, so the shadow of the hand also
had a large effect. The whole system would very rapidly seek positions
where the balances of heat and light came into equilibrium with the
carriage position. Both heat and light disturbances, such as from a
cigarette lighter, would seem to make the carriage move in strange ways to
new positions, sometimes slowly and sometimes very rapidly. If approached
from the right direction, the thermistors would do nothing until actual
contact was made, and then jerk suddenly away from the finger, or into it
and beyond it (the thermistors were sticking up on the ends of flexible
wires). All kinds of purposive interpretations could be offered: the
carriage was trying to keep the finger between itself and the window, the
touch caused a startle response, the carriage was chasing the finger or
fleeing from it, and so forth. But the students, having seen how each part
of the system worked and having gained a personal intuition of the system
through physical interaction with it, quickly arrived on their own at the
_correct_ purposive interpretation: that the system was controlling some
function of heat and light sensor signals. Of course now they would all
have to be told that the system was retrofacting light and sensor signals,
since if they said "control" some people would interpret this to mean
"react"
or "affect" or "influence" or "determine" or "cause." The students knew
that what they had experienced was none of these. What they had been
experiencing had never been mentioned in any of their psychology or
philosophy courses.
------------------------------------------------
I still try to teach through demonstration, but it's hard to get people on
the internet to explore the simple demos to get the kind of understanding
my students eventually got. Everyone wants to go on to more interesting
topics, big complicated systems doing big dramatic things, and generally
doing things that are deliberately made so complex that they can't be done
well, or be understood in any clear way. It's almost as if people want to
avoid the simple issues, the clear phenomena, the explanations that either
fit or don't fit with no quibbling. As long as we flounder around with
complex behaviors, any theory about them can seem right -- who can prove
they're wrong?

Bill Leach at one time was considering building some real servomechanisms
to use as demonstrations of real retrofactive systems that people could
physically interact with. I hope, Bill, that when your current situation
comes to some sort of even keel you can get back to this project. Even if
they cost $500 apiece, they would be worth it in educational power. People
who are serious about wanting to learn and teach retrofaction theory would
willingly pay the price to buy or rent such devices.
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Matti
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