Stepper Motors and Power Supplies

We get a lot of questions about what stepper motors and power supplies to use, so we've started this page. As of today (1/19/14) it's pretty sketchy but we'll fill this in. A lot of this information is scatter over the rest of the wiki, but it's nice to pull it together in one place.

Stepper Motors

Sources

Here are some sources that carry some good motors. Please feel free to add your favorites.

• Alltronics See the OSM's in particular. Often have some interesting surplus Lin motors. Have NEMA8's
• Pololu Have some nice smaller motors as well, e.g. NEMA11
• Sparkfun
• Phidgets
• Oriental Motor Company
• Automation Technologies (Keling) In particular they carry a 425 oz-in NEMA23 that only takes 2.8 amps. Monster.
• Automation Direct. Check out the STP-MTR-17060, a 125 oz-in NEMA17
• [MPJA](http://www.mpja.com/Stepper-Motors/products/101/ www.mpja.com/Stepper-Motors/products/101/) Surplus motors
• [All Electronics](http://www.allelectronics.com/make-a-store/category/400/Motors/1.html www.allelectronics.com/make-a-store/category/400/Motors/1.html) Surplus motors

References

More some useful information on steppers and wiring steppers:

• http://reprap.org/wiki/Stepper_motor

General

NEMA17 versus NEMA23

TinyG is capable of delivering 2 amps per winding, and 2.5 amps per winding with cooling. Given that, we have never found a NEMA17 that would not work with TinyG, and almost every NEMA23 we have tried will work if rated up to about 3 amps per winding (with the caveat that you might not get full power if it calls for more than 2.5 amps). We also routinely run NEMA34's, but not at full power and therefore not in high mechanical load situations.

What's with the motor's rated voltage?

The question comes up - can I run a motor with a rated voltage of 4.2 volts (for example) with a 24 volt supply? Will this burn out the motor?

The motor's rated voltage is irrelevant and can be ignored.

When running NEMA23's (or above) we recommend fan cooling. Note that most of the heat comes off the bottom copper, so be sure to provide air circulation for the bottom as well as the top.

Finding the Coil Pairs on a stepper motor

Bipolar motors have 4 wires (2 pairs), Unipolar motors typically have 6. Some other motors have 5, or 8, or whatever. 8 wire motors are usually wired as 2 sets of bipolar windings (i.e. essentially 2 bipolars wired together). 5 wire motors are usually in a "star" configuration that has a common ground and require a specialized driver. TinyG cannot drive 5 wire steppers.

The following color code is typical for many motors

	Color    | Bipolar      | Unipolar      | Notes
	---------|--------------|---------------|--------
	Green    |  Winding A1  | Winding A1    |
	Yellow   |  (none)      | Center tap A  |
	Black    |  Winding A2  | Winding A2    |
	Red      |  Winding B1  | Winding B1    |
	White    |  (none)      | Center tap B  |
	Blue     |  Winding B2  | Winding B2    |

Use your volt meter to verify that green and black connect together, and red and blue connect together, and that they don't connect to the other pair. Typical DC resistance across a winding is about 1 to 5 ohms. If you have a Unipolar motor you can just leave the center taps disconnected.

If this doesn't work here's a shortcut to finding wire pairs for a bipolar (4 wire) motor.

Spin your stepper motor with your fingers. Depending on the size / holding torque this could be easy or pretty hard. All you really want from this is to get a feel how the motor spins without any of the wires connected to each other. Now that you know how hard it is to spin with your fingers, connect 2 wires together. Just pick any two. Try to spin the motor again. If it feels the same then more than likely these are NOT connected to the same coil. Disconnect these wires. Connect one of the other wires to one of the first wire pairs you tried. Try to spin the motors again. This should be much harder. If so, you have found your wire pairs. Tape these 2 together (not wired but just taped to group them). Tape the remaining 2 wires together as well.

Unipolars are a bit more complicated, but not much. To do a series wiring find the outer taps of each coil. These are often color coded by convention (see below). Using a volt meter to find the resistance across the outer pair. The resistance between the center tap an an outer tap will be 1/2 the resistance between the outer taps.

Power Supplies

References

Sources

General