I see this (am I using the correct term?) in reference to motorizing turntables and other slow motion animation projects.
What is it and how does it differ from a regular DC motor?
A stepper isn’t a free-running motor. It usually has three or more “legs” or discrete winding sections. Driven by a transistorized or integrated circuit, it can be “stepped” forward or backward in very precise increments.
Here’s a link to a nice pdf on the subject:
http://www.solarbotics.net/library/pdflib/pdf/motorbas.pdf
and here’s one in the Wikipedia:
http://en.wikipedia.org/wiki/Stepper_motor
FOR TURNTABLES better (and cheaper) to use a geared motor and a SPDT toggle with spring loaded CENTER OFF.
One example of an extremely accurate stepper motor is the Idle Air Controller on GM and some Toyotas. Here is a link to some info: http://www.autoshop101.com/forms/h26.pdf
Jim
Ford is using them in electronic throttle bodies now.
Stepper motors are usually controlled by sending two trains of digital pulses, which are 90 degrees out of phase with one another. Which channel of pulses is “ahead,” that is, goes positive before the other, determines the direction the motor will run. The frequency, how fast the signal is pulsing, determines the velocity of the motor. The steppers we usually see from disk drives, or surplus sites, don’t usually have a lot of torque. Additionally, they may not come with documentation. Since there are two basic types of stepper, which are controlled differently, this can be a problem.
Providing the trains of pulses is usually done by a piece of electronics called, appropriately enough, a stepper motor controller. Counting the number of pulses, determining the frequency and phase of the digital pulses, etc. is the job of the controller. You just tell it how fast, which direction, and where to stop. But you still have to do that digitally, so you’re dealing with a microcontroller, or microprocessor. Then you’ve got software to write, a control interface to design and build, etc. While it’s definitely do-able, it’s a fairly involved task, not a one-evening project.
Appropriate microcontrollers for this sort of thing, and stepper motor controllers, can be found at websites like the following:
Parallax: Basic Stamp http://www.parallax.com/
Savage Innovations: OOPIC http://www.oopic.com/
There are a great many other candidates. These have the advantage of programmability in higher level languages with Basic-type syntax. Good places to learn more include robotics websites, and the magazine Nuts & Volts, which can be found at Borders or Barnes & Noble, among other places.
-Ed