Subject:
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Re: Building a Postscript printer?
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Newsgroups:
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lugnet.robotics
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Date:
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Tue, 27 Jun 2000 17:49:57 GMT
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Viewed:
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836 times
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> Looking around the newsgroup, I found some posts talking about stepper
> motors (including that cool LEGO-only motor). So what is the consensus
> then? Can we control a stepper motor using LegOS+hacking or can we
> do it with the standard firmware? I'm also clueless about the difference • between
> a servo and a stepper.
Let's try a little "metaphor". Not technically correct, maybe, but we'll see
:
1. servo motor
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A servo motor is esentially an "analogic" device : you have to provide him
with a pulse width modulated signal. The signal must be logical 1 (5 volts)
for 2-5 msec, and logical 0 (gound) for 20 msec (20msec not critical). The
variable 2-5 msec length of the signal gives the position of the axis. You
cannot make more than +- 250° (less than one turn) with a servo motor
without tweaking it. Because the internal circuitry uses a potentiometer to
control the position. You also need to provide external power. (3 wires for
most servos)
You could eventually tweak the servo and connect directly the pot to the
rcx inputs and control the motor directly while watching with the rcx where
is the axis).
If you remove the plot which lock the axis, you can have a servo which can
make multiple rotations.
2. Stepper motors.
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When interfaced with proper interface, stepper motors are essentially
"digital" devices (or at least "look like"). In fact, using a specialised
IC, you can control most of them (those found in floppy drives for example)
with only three wires :
- One which means one step left
- One which means one step right
- One which means half-step (double precision but less torque I guess)
Conclusion :
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Interfacing a stepper motor would require to build an interface using a
specialized ic. (A stepper motor driver). This is the easiest solution
providing the rcx has only 3 outputs. Those outputs should be multiplexed.
Connecting a servo motor is difficult : the 2-5 msec timing is too short for
the standard hardware. With some replacement firmwares such as legos or
pbForth you could control servo motors directly (expectations here). I think
it has already been made.
In your case, you'd better use stepper motors altough you'll need some more
electronics. because you need a motor which is able to make more than one
turn.
But maybe it's an overuse of those hi resolution motors : using lego gears
with a stepper motor is quite "strange". Maybe with standard lego motors and
rotation sensors you would get the same resolution using only genuine pats.
Just my 0.02
Philippe
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Message is in Reply To:
 | | Re: Building a Postscript printer?
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| Thanks! I grabbed the HPGL info from wotsit.org. Looking around for Postscript->HPGL converters, I found the following: <ul> <li> <a href="(URL)Pstoedit</a>: converts Postscript and PDF into lots of other vector formats (including HPGL). Source (...) (24 years ago, 24-Jun-00, to lugnet.robotics)
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