Communicate with stepper motors?

[Stephen Barncard]

I worked with a lot of stepper motors in my days in the movies 
working with Jim Cameron in the early 80's.

You don't want to create the pulses yourself unless you're trying to 
prove something.

Stepper motors require a lot more than 'electrical pulses' sent to 
it. They also would need anywhere from 0 - 5000 pulses per second. 
But the killer part is that steppers need to be RAMPED. That is, they 
need to be started slowly and ramp to speed. So what you need is a 
stepper motor controller to create the pulses.

If you're good with a soldering iron, you can create a controller this way
http://www.controlchips.com/cy545.htm
These are reasonably cheap.

Also stepper motors consume current. YOu can't just take the output 
of an interface directly to a motor. It takes driver transistors and 
a high current low voltage supply to make it work. There are often 4 
or even more  coils to feed, and they must be fed a perfect square 
wave at the right time and in the right sequence, like an internal 
combustion engine.

Superior Electric used to make the packaged products to drive 
steppers that I used at New World Pictures. These are pretty 
expensive, but they contain all you need to drive a motor from a 
computer serial port.
http://www.danahermotion.com/products/product_detail.php?parent_id=549

Finally, you have to decide on a strategy of feedback. That is, you 
need to keep track of the absolute position of whatever you're 
controlling. If it's just 360 degrees, that's one thing. BUt if it's 
controlling a camera running down a track, then you need an external 
way to keep tabs on where you are. For that end one usually uses 
encoders.

Also another alternative might be a DC SERVO which works inside a 
feedback loop. Offset the loop plus or minus voltage and the motor 
runs. Encoders are part of the package. Servos are more accurate and 
can deliver more torque quicker.

>I was talking with a guy yesterday who said that using Basic you 
>could use the printer port on Windows to talk to a stepper motor. I 
>know pretty much nothing about robotics (or communicating through 
>ports for that matter). Does anyone know if this is possible with 
>Rev? I read through the docs and could see that one can read from 
>and write data to com ports and LPT ports, but wouldn't a stepper 
>motor just need electrical pulses sent to it?
>
>I realize I'm revealing my ignorance to the world here, but any help 
>would be appreciated.
>
>Marty Knapp

-- 
stephen barncard
s a n  f r a n c i s c o
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