From: Trevor Jacobs (firstname.lastname@example.org)
Hi John and all,
How big of a motor are you planning on driving? If you are using a size 17 motor rated at say 12 VDC you could build up a small drive circuit out of 2N2222's or similar with some logic to run it.
One chip that you could use is the Ericsson PBD 3517 (now manufactured by NJR in Japan). It will drive a stepper in unipolar (6 wire) fashion with a minimum of external components. Two signals are required to run the chip: Step and Direction. Think of step as a clock pulse, each pulse steps the motor 1 full step (or a half step if in half step mode). Direction is either high or low depending on which direction you want to turn the motor. The pulses could be generated easily with a 555 timer.
Now, keep in mind, that you have no idea of the position of the motor at turn on, so if you want to store motor positions you'll need some kind of "Homing" routine at power up. I usually run the motor to one end of travel and use some kind of sensor to know when it's there. This could be as easy as a microswitch with an arm attached to the motor (assuming 1:1 gearing or direct drive) to trigger the switch when at the home position. After the motor is homed, you simply "count" the number of steps that you move. If you don't want to store motor positions, you'll still need to know when the motor is at the end of the travel of the device (I'm assuming an air variable?) so that you don't destroy what you are driving. You could use micro switches for this also or a hard stop on each end of travel that keeps the motor from turning any further. The latter method will NOT damage the motor and is common practice.
As far as resolution goes, the most common size 17 motors are 1.8 degrees per step. If you need further resolution, you could half step the motor with the above chip to get .9 degrees per step. Higher resolution motors are available, such as .9 degree per step motors, but the torque is generally much lower for the same power rating and stack size.
For very high resolution, you could look into microstepping. I commonly use 1/128th or 1/64th microsteps per 1.8 degrees for my applications. This gets way more involved though.
One very good source of information and parts for stepper experimenting is http://www.eio.com . They offer a wide variety of parts and there is also a news group.
Sorry for the long winded e-mail. Hope this helps...
From: "John Dorson" <JDORSON@worldshare.net>
Date: Thu, 6 Sep 2001 13:11:17 -0400
To: "Low Power Amateur Radio Discussion" <qrp-l@Lehigh.EDU>
Subject: motor control
> can anyone tell me where I can find a stepper motor and control. I wan to
> add this to my loop antenna.
> John K2JHU...
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