XY Table Part 6: Determining Stepper Configuration

Since I couldn’t find a datasheet on my Sanyo Denki stepper, I decided to figure out how the motor was wired myself.  There are a variety of sources; PIClist has the best list of methods I found, and RepRap is also worth a look.

If you’re not familiar with stepper motors and their terminology (such as unipolar or bipolar), Wikipedia’s article is a good start.  A 4 wire stepper can be used in bipolar mode only, a 5 wire stepper can be used in unipolar mode only, but 6 and 8 wire steppers can be used in either bipolar or unipolar mode.

The exact procedure to use will vary depending on the motor (and its number of leads) and the equipment you have.  Since I have an 2 channel oscilloscope, I decided to use it and look at the phase differences between the leads of my Step-Syn 103-771-16.

My Step-Syn is a 5-wire stepper motor so it has one common wire connecting the center-taps of both coils, and four wires connected to the ends of the two coils.   The wire colors are black, red, blue, yellow, and orange.

The first step is to find the common wire:  the resistance between the common wire and any other wire will be half of the resistance between any other two wires.  The resistance  between the black wire and the other wires was 130 Ohms; between all the other wires, 260 Ohms.  So the black wire is the common.

The next step is to set up the oscilloscope with the black (common) wire connected to the oscilloscope probes’ ground and the two channels connected to any two wires.  You then spin the motor and adjust the oscilloscope settings (V/Div, timebase, triggering, etc) until you can capture a good set of data.  If the waveforms are 180 degrees out of phase, the wires are from the same coil.  If they are 90 degrees out of phase, the wires are from different coils.

If your oscilloscope can be used in XY mode (often used for showing Lissajous patterns), it’s even more obvious: wires from the same phase create a diagonal line while wires from different phases create a circular pattern.  My Fluke 196 doesn’t have a real XY mode, but I used a Tek TDS210 to get the pictures below.

If the wires are connected to the same coil, then the other two wires are the other coil.  If the wires are connected to different coils, then swap out one wire until you find two wires on the same coil.

Suppose I connect the Step-Syn’s orange and yellow wires to the scope.  The scope trace would show they are connected to the same coil; therefore, the other two wires (red and blue) are the other coil.  Or, suppose I connect the orange and blue wires to the scope; the trace would show they are connected to different coils, so I would swap out one wire (for example blue for yellow) and try again until I find two wires connected to the same coil.

The procedure would be similar for a 6-wire stepper motor, except you have to find two common wires, but the procedure would be considerably more complex for an 8-wire stepper.

The final part is determining the how to connect the wires to the driver.  Basically, connect the coil wires up using your best guess.  If you swap wires within a coil or swap the coils you will change the direction of rotation.  I’ll give a real world example in a paragraph or two.

When I got ready to connect my Step-Syn motor to my Stepnet I discovered I had a problem: the motor is unipolar only while the Stepnet is bipolar only.  The Stepnet manual doesn’t state that (there is no mention of bipolar or unipolar stepper motors), but it became obvious when I looked at the motor connection diagrams in the manual.

Sometimes you can convert a 5-wire motor to a 6-wire by taking the motor apart, cutting the connection between the two center-taps, and then bringing out the second center tap.  I did take the case off the Step-Syn, but I didn’t see any obvious way to bring out the sixth wire.

Since I still wanted to test this motor, I decided connect it to a Allegro Microsystems UCN5804 unipolar stepper driver.  I connected the black wire, Pin 2, and Pin 7 to +24VDC, orange to Pin 1, yellow to Pin 3, blue to Pin 6,  red to Pin 8, and Pin 14 (Direction) is tied to ground.  The motor rotated the direction I wanted: clockwise when viewed from the front.  Using the UCN5804 datasheet, I determined that in 2-phase drive the wires were energized in the order yellow/red, red/orange, orange/blue, and blue/yellow.  In wave mode (1 phase), the wires were energized in the order red, orange, blue, and yellow.

Swap two wires within a coil, for example, yellow and orange.  yellow is now connected to Pin 1 and orange is connected to Pin 3.  The motor now moves counter-clockwise.

Related posts:

1. XY Table Part 4: Stepper Motors
2. XY Table Part 5: Finding Information
3. XY Table Part 3: Major Components
4. XY Table Part 2: Overall Architecture
5. XY Table Part 1: Introduction