EB-011 & Stepper Motors

[JohnCrow]

Hi

I'm looking at driving a stepper motor with the L293D chip configured as on the EB-011 Power Board.

After looking at various circuits etc I just want a conformation that I have understood everything and I'm not going to release the magic smoke
The motor is a 4-phase unipolar (6wire) (Rapid Part No. 37-0506)

As I see the connections using 1 half of the E-block

EB-011.....Motor Connections
0...........Brown....(A1)
1...........Red.......(A2)
2...........Orange...(B1)
3...........Yellow....(B2)

The two center taps from the motor are both tied to the 12V supply at the same point as the 12V PSU is connected to the EB-011

The motor draws 160mA / phase = total 320mA.
I appreciate the Matrix supply (500mA) will be on the limit of its current capacity so to drive the motor so I will need a seperate 12 V PSU

I can then control it using the +ve unipolar macro in flowcode, using 4 data lines from the EB-006

Thanks

[Sean]

The motor is a good match with the L293D.

If the common wites are connected to the 12V supply, the 'Unipolar -ve' configuration option should be selected (-ve logic used for the output signals). Alternatively, the common wires could be connected to 0V with +ve polarity signals sourcing the coil currents.

Note: The L293D contains free-wheel (back emf) protection diodes. Some other versions of the L293 have a higher output current specifications, but no protection diodes. The diodes are necessary when switching inductive loads and would need to be added externally.

[JohnCrow]

Ive finally got round to getting a EB006 board.
Ive connected it up as in my last post using +ve unipolar, and it works fine.

But i managed to catch the common wire and disconnect them from the gnd on the EB-006 but the motor kept stepping.
I have measured the connections and they are wired as above. So I dont understand why it kept working with the common disconnected?

[Sean]

If the common connections of a uni-polar stepper motor are not used, some motors can behave as bi-polar motors.
The common connections are effectively centre-taps in coils from A to B, and from C to D. When the commons are connected, each of the four coil connections only requires a uni-polar drive (open-collector transistor) to energize it.

Disconnecting the commons can allow current to flow directly between A and B and between C and D. This will only work if totem-pole drives are being used (L293, L298 etc.). The bi-polar arrangement is effectively 2 uni-polar coils in series, so the voltage and current characteristics will change. This might not be noticed if the motor is not under mechanical load.

[JohnCrow]

Thanks Sean

Ive just got the motor on the bench, and not driving any loads at the moment.