My Stepper motor is just jiggling!

Using Arduino Motors, Mechanics, Power and CNC
1

I'm pretty new to arduinos and I'm trying to get a stepper motor moving. I got an Airpax 12V stepper that I can't find any data sheets for. I used an multi-meter to find the leads using the method from this site

http://www.me.umn.edu/courses/me2011/arduino/technotes/stepper/index.html

I ordered some darlington ULN2003AN transistor array chips and hooked everything up through that with a 9V cell phone transformer (my meter tells me that it actually provides about 13V).

Here's the code that I used, it's simple and there were no obvious problems with it.

#include <Stepper.h> 
#define STEPS 48
Stepper stepper(STEPS, 4,5,6,7);

void setup()
{
  int i;
  stepper.setSpeed(30);
  delay(1000);
  stepper.step (48);
  delay(1000);
  stepper.step (-48);
  delay(1000);
  stepper.setSpeed(60);
  for (i=0;i<5;i++){
    stepper.step(20);
    stepper.step(-20);
  }
}

void loop()
{}

I'm trying to just get this motor moving before I try to do anything with it but when I hook it up to the power supply and start the arduino, the shaft just jiggles. It jiggles in spurts twice, then jiggles a little faster leading me to believe that the code is reaching the
motor, but something's not working and I can't figure out how to trouble-shoot the problem. The transistor array also gets real hot real fast and that doesn't seem quite right. Any thoughts or suggestions would be greatly appreciated.

Jeremy

2

Switch two of the wires, any two will do.

3

Thanks. I feel like a bonehead. I had my wires mixed up. I got the motor turning but my chip was still heating up too hot and too fast. I threw a resistor between the power source and the chip (leaving full power to the motor) and it stopped getting so hot. I'm not sure if this messes with anything that I'm not seeing. The motor seems to be working fine, plenty of torque, and nothing is getting so hot.

4

What chip is/was getting hot?

5

If the motor driver chip was getting hot then your motor is drawing too much current for the driver chip. Have you searched the web for any info? what info is on the motor?

6

The chip is a Texas Instruments ULN2003AN chip. The stepper motor is an Airpax 11.9 volt motor. I've searched every bit of info on the sticker for the motor and haven't been able to find anything. There is an Ohms/Coil number which is 33.5. Does this help at all?

7

33 ohms is not unreasonable, that's about 350mA per winding at 12V. You can always measure this
to check the markings are correct :wink:

The ULN2003 has darlington outputs, it will get hot at 350mA - so long as its under 100C its going to
function OK (heatsinking and/or forced air cooling would help). 4 discrete switching transistors rated
at 1A each and driven with 20mA base current would be probably be more efficient and run cooler.

You could double-up two ULN2003's in parallel to share the current and reduce temperature - they
are cheap enough.