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### Topic: 8-wire stepper motor STH-56D111 (Read 2127 times)previous topic - next topic

#### zeropoint

##### Jul 31, 2012, 03:50 pm
I couldn't find a datasheet or much wiring info for the Shinano Kenshi STH-56D111 Stepper motor so I'll put what I have here along with the logic that got the 8-lead stepper to run in Bipolar series.

Key:
G=Green B=Black O=Orange W=White w=[white wire with colored stripe] c*=coil ,=connected wires <->= opposite poles

Coil wire pairs(19ohms):
c1 = R <-> B
c2 = Rw <-> W
c3 = G <-> O
c4 = Gw <-> Bw

Parallel coils:
c1+c2 = R, W <-> B, Rw
c3+c4 = G, Bw <-> O, Gw

Series coils:
Coil A
(A+) = Bw
(A-) = O
Center tap = G,Gw
Coil B
(B+) = W
(B-) = B
Center tap = R,Rw

I found each of the coils by measuring resistance on each of the wires. Since there were 4 wire pairs each with 19 ohms, I figured I was working with 4 separate coils. I soldered 2-pins on each of the pairs and powered up a breadboard rail with 1.5V (25% of the motors' rated voltage). I plugged in 2 coils at a time and felt how much force it took to turn the motor. After a bit of plugging, I found that c1 and c2 had the most force together, as well as the least force when the polarity of one coil is reversed. That told me that the coils were relatively on-axis with each-other. Combination of c1 with c3 or c4 resulted in ~25%-75% force regardless of the polarity of the second coil, this told me c1 was off-axis with c3 and c4. I applied the same logic to find c3 on-axis with c4.

To put the pairs in series you just keep the current flowing in the direction that has the most force. You obviously don't want the parllel coils to directly cancel each-other out at any point.

Since I kept driver 1 and 2 separate on the L298N proto-board there was a 50% chance that my motor would spin and not just jerk back and forth between steps. As well as a 50% chance that it would actually turn in the right direction. It performed flawlessly on the first try, I was astounded.

Of course, if you have a 4-channel oscilloscope laying around you can spin the motor by hand and see the exact timing and polarity.

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