Regarding that motor control stuff...
Archiver
Posts: 46,084
Hey group-
Thanks for all the replies I received regarding implementing multiple PWMs with
a BSII. I'm leaning heavily in the direction of an AWC PWM coprocessor, since
it's a single-chip solution with multiple PWM outs. Some of the other stuff
people suggested had only one PWM out. Another suggestion, the Oak Tree
coprocessor, seemed superior to the AWC PWM coproc, but it needed its own PCB,
and I really needed a 1-DIP answer. Someday I'll probably learn PIC ASM and
make a Serial Motor Controller, possibly with the drivers built into a circuit
board, ... but that's for another year.
I have one more nearly unrelated question.
Assume that I have a DC motor shaft that must be rather loosely controlled, as
in accuracy to the nearest 10 degrees is fine. Positional control of the shaft
will likely come from a joystick, as inverse trig functions make angle
determination (read desired position) easy to do. The joystick angle should be
the exact same as the rotation of the output shaft. If not, the stamp with
motor control tasks will continually update the shaft position until it reaches
the desired angular position.
->Some possible solutions I've thought of:
1. The easiest: an absolute shaft encoder. I've never seen one these things in
any catalog and I'm sure they're darned expensive. But I've heard them
mentioned in books...
2. A geared-up servo. If the user wanted continuous rotation this wouldn't
work. So it won't work for this application, but maybe with similar ones.
3. Two-phase shaft encoder. I like! Reasonably accurate control, but would
require a reset upon startup, where the shaft would turn until a switch is
pressed, and the BSII knows its position. Another potential problem: accuracy
loss over time.
4. I just thought of this, it sounds interesting to try out. I know that some
potentiometers can be bought without mechanical stops limiting their range of
motion. Assuming >180degree range, place one on the shaft. Then place the
second on the same shaft, just 180 degrees out of phase from the first. When
one pot reaches its lower or upper limit, you would know to use the other one's
reading to determine position. Sounds cheap, and would probably require little
programming complexity. However, for endless rotation pots, when they're
outside of the measurement range, what happens? I'm guessing the circuit opens,
but I don't know.
Known to not be solutions:
1. A normal potentiometer is out of the question, since rotation tends to be
limited to less than 280 degrees.
2. Steppers require more circuitry, and the shaft will definitely be a DC
motor.
I don't know if any mechanical engineers are on the list, but I thought I should
ask the question anyway, since it's an electrical problem too. As always, any
suggestions are appreciated!
-Brandon Heller
Montgomery Blair High School
Thanks for all the replies I received regarding implementing multiple PWMs with
a BSII. I'm leaning heavily in the direction of an AWC PWM coprocessor, since
it's a single-chip solution with multiple PWM outs. Some of the other stuff
people suggested had only one PWM out. Another suggestion, the Oak Tree
coprocessor, seemed superior to the AWC PWM coproc, but it needed its own PCB,
and I really needed a 1-DIP answer. Someday I'll probably learn PIC ASM and
make a Serial Motor Controller, possibly with the drivers built into a circuit
board, ... but that's for another year.
I have one more nearly unrelated question.
Assume that I have a DC motor shaft that must be rather loosely controlled, as
in accuracy to the nearest 10 degrees is fine. Positional control of the shaft
will likely come from a joystick, as inverse trig functions make angle
determination (read desired position) easy to do. The joystick angle should be
the exact same as the rotation of the output shaft. If not, the stamp with
motor control tasks will continually update the shaft position until it reaches
the desired angular position.
->Some possible solutions I've thought of:
1. The easiest: an absolute shaft encoder. I've never seen one these things in
any catalog and I'm sure they're darned expensive. But I've heard them
mentioned in books...
2. A geared-up servo. If the user wanted continuous rotation this wouldn't
work. So it won't work for this application, but maybe with similar ones.
3. Two-phase shaft encoder. I like! Reasonably accurate control, but would
require a reset upon startup, where the shaft would turn until a switch is
pressed, and the BSII knows its position. Another potential problem: accuracy
loss over time.
4. I just thought of this, it sounds interesting to try out. I know that some
potentiometers can be bought without mechanical stops limiting their range of
motion. Assuming >180degree range, place one on the shaft. Then place the
second on the same shaft, just 180 degrees out of phase from the first. When
one pot reaches its lower or upper limit, you would know to use the other one's
reading to determine position. Sounds cheap, and would probably require little
programming complexity. However, for endless rotation pots, when they're
outside of the measurement range, what happens? I'm guessing the circuit opens,
but I don't know.
Known to not be solutions:
1. A normal potentiometer is out of the question, since rotation tends to be
limited to less than 280 degrees.
2. Steppers require more circuitry, and the shaft will definitely be a DC
motor.
I don't know if any mechanical engineers are on the list, but I thought I should
ask the question anyway, since it's an electrical problem too. As always, any
suggestions are appreciated!
-Brandon Heller
Montgomery Blair High School
Comments
> From: northstarb@a...
It's not entirely clear to me how many degrees your motor
will turn or if it's continuous rotation both directions.
Most of this type of problem has been turned over to optical
digital devices called shaft encoders. [noparse][[/noparse]look in your catalogs
and in the Stamp archives for descriptions].
There are 3, 5, 10, 20 turn pots that have high resolution
[noparse][[/noparse]and cost unless surplus]. These are spiral wound inside -
some with ball bearings. Also the continuous pots in single
turn come tapped or regular and don't have a large gap per
turn going from max to zero in a very small degree. They
are subject to eventual contact noise [noparse][[/noparse]though wirewound and
with precious metal contacts...] and mechanical wear after
many thousands of turns.
Have fun!
________________________________________________________________
YOU'RE PAYING TOO MUCH FOR THE INTERNET!
Juno now offers FREE Internet Access!
Try it today - there's no risk! For your FREE software, visit:
http://dl.www.juno.com/get/tagj.
> Hey group-
> Thanks for all the replies I received regarding implementing
multiple PWMs with a BSII
>Another suggestion, the Oak Tree coprocessor, seemed superior to the
>AWC PWM coproc, but it needed its own PCB, and I really needed a 1-
>DIP answer.
Just to clarify, our low-end coprocessor comes with a PCB, but you
don't have to use it if you don't want to! Just put the chip on your
own project board and connect the required support components
(resonator and reset circuit basically) according to the schematic.
Chuck Davis
www.oaktreesystems.com