You’ve got to move: working with motors
I’m working on several projects, where in each case, my role involves making a motor spin. On one project, we need a small motor, running at approximately 33RPM. At first, I chose a Mabuchi DC motor, one inch in diameter. This type of motor wants to run fast. To slow it down, I throttled back on the input voltage. At five volts no load, the motor spun too fast. At four volts, it didn’t turn.
Powered this way, the motor had little torque. Not surprising, since the operating voltage was 8 – 18v. The application called out for either a gear head motor or a stepper motor. The gear head motor would be a motor much like the Mabuchi motor I used, with the addition of reduction gears to let the motor spin fast while the gear train slows down the effective rotation and increases the torque output. The drawback was that gear head motors are bulky plus I didn’t have one at hand.
I managed to scrounge a Moon’s stepper motor. It’s a 24v bipolar 4-wire motor. It is a squat motor, approximately the same diameter as the Mabuchi. Stepper motors, of course require a specialized drive circuitry. Luckily I had a left over EasyDriver (http://www.sparkfun.com/commerce/product_info.php?products_id=8368) from an old project. For the hobbyist or prototype builder, the Easydriver simplifies the use and control of a stepper motor. I have an older version of the EasyDriver. The EasyDriver has two control inputs: Step and Direction.
A short while ago, I was in a pinch to demo the Moon’s set up. I needed a 5v pulse input signal for the EasyDriver. From the Allegro datasheet “A low-to-high transition on the STEP input sequences the translator and advances the motor one increment.” All I had at hand was an Arduino clone. A quick mod to the Arduino LED Demo Program and the motor was spinning.