I have two used flatbed scanners that I've taken apart and retrieved stepper motors from, but they are not identical. One is a unipolar motor, and the other is bipolar. I have already wired up and tested each motor individually (ULN2003 for the unipolar, L293D for the bipolar), but can't seem to get them both to run at the same time.
I have a simple sketch that uses the AccelStepper library to make each motor move forward, then back an equal amount. However, depending on the type of power supply I use, only one or the other motor will actually spin.
When I connect my USB programming interface to my Arduino, I am able to measure 3.9V at the stepper driver chips, and the bipolar motor moves (unipolar motor does nothing). When I disconnect the programming interface and switch on my external power supply (+5V line from an ATX power supply), I measure 4.6V at the driver chips, and the unipolar motor spins (bipolar motor does nothing).
I was unable to find the datasheets for either of these motors (the markings are pretty unhelpful), so I just guessed that they ought to be able to run in some capacity at 5V.
How can I control both of these motors at the same time, using the same power supply? Do I need to go through the trouble of building an adjustable power supply to supply different voltages as needed, or is there a simpler trick I can try?
h4t:
I was unable to find the datasheets for either of these motors (the markings are pretty unhelpful), so I just guessed that they ought to be able to run in some capacity at 5V.
How can I control both of these motors at the same time, using the same power supply? Do I need to go through the trouble of building an adjustable power supply to supply different voltages as needed, or is there a simpler trick I can try?
Steppers are not dependent on their driving voltage and 5V should be safe. If 5V is too low the outcome with either be that the motor will not run with its full speed or torque and if 5V is too much (assuming a non-current-limited drive) then the motor will start to get too hot.
@yolser - I'm sorry, I'm not sure I understand what you are asking. The wiring is fine, I've already figured out which wire goes to which phase, and how to wire up the chips appropriately. I had a previous thread on the topic which can fill you in: http://arduino.cc/forum/index.php/topic,114843.0.html
@Chagrin - that's what I thought. Any ideas on why only one motor will work at 3.9V, and the other at 4.6V? Perhaps its a matter of insufficient current, but I thought that ATX supplies are capable of multiple amps per power line.
In the past, I had tried to run my unipolar motor (connected through a ULN2003) at 12V, and it DID run, but it (and the driver) got much too hot. At 3.9V (USB), it doesn't move at all, and at 4.6V (ATX supply) it runs fine.
Remember that if you drive it at a low voltage then it won't pull its rated current, and generally speaking with motors voltage equates to speed and current relates to torque.
If you run any stepper at higher than its rated voltage you must use some sort of current limiting or it will get too hot. You can measure the resistance through any single coil, and knowing the voltage rating, calculate the amperage rating that way (using Ohm's law). Typical methods of current limiting with steppers is to use large ceramic resistors in line with the coils (wasteful) or a "chopper" drive which will limit the current. Drivers based on the Allegro A4988 are very popular and can be used with bipolar or 6 or 8 wire unipolar motors wired in a bipolar configuration. 5 wire unipolar motors cannot be wired in a bipolar configuration.
Any ideas about why a motor would work at 3.9V, but not at 4.6V? As I said, when I run both motors off my ATX power supply's 5V line, only one motor will work. When I run them with my USB connection plugged in, the other motor works, but the first one stops working.
One motor is a 5-wire unipolar, the other is a 4-wire bipolar. I've already invested in a ULN2003 and L293 to drive them, so I'd rather not spend $30+ more if I don't have to.
Theoretically, BOTH motors SHOULD work at 4.6V (ATX supply), but only one will. The motor that does not work makes some effort, but doesn't get anywhere. This motor DOES work at 3.9V. What might that mean?
The images show my latest test, of running both chips on 12V (hence the orange jumper between the two). This didn't work - one motor doesn't turn, the other gets way too hot.
