Problem with Pacific Scientific Motor

[ChuckNRC]

Hi I'm having a problem with a Pacific Scientifc hybrid stepper motor we purchased a few weeks ago.  This is more a total hardware question than with Labview so I hope its ok to post in this forum.

We actually purchased two steppers and I do have 1 working.  Both gave similar problems.  When hooked up to the drive box they didn't work (the drive box was set to turn clockwise 2 revs and then 2 revs counter clockwise).  After playing with it a bit we tried switching the A and A(not) leads.  This worked.  Thinking that Pacific screwed up their wiring diagram (strange, but ok), I wired the second motor the "right"

way and it didn't work.  I tried reversing the A and A(not) leads now thinking that ok maybe the first motor was wired wrong (orange should have been black).  That didn't work.  I then proceeded to try every possible combination (switch the As, switch the Bs, switch both As and

Bs).  Nothing worked.  I've used an ohm meter across both coils and they seem ok (nothing is open, about .4 ohms).  I also tried hooking up just the A coil and then just the B coil.  This is the only place where I noticed something a little unsual.

If I hook up just the B coil it tries to turn (makes a noise, but can't turn without the other active), but if I hook just up the A coil nothing (no noise).  I tried this with the other working motor and it made noise with just B and with just A coils hooked up.

I don't think I could have broke the motor (I've tried pretty much everything on both motors and the working one still works), but does this mean the one is broken, or is it just stuck or has anyone had a similar problem?

Thanks in advance

Chuck

[Buechsenschuetz]

First, it is not easy to break a stepper motor if you don't burn the coils - this will only happen if you feed them with excessive current. If you have very similar resistance readings on all motor coils they still seem to be OK. When measuring very low resistance (less than 1 ohm) you also should check offset error and cable resistance of your instrument, this usually will contribute a few tenths of an ohm, too.

When you activate just one coil with a stepper motor driver you cannot be sure what will happen. Sometimes the motor will move (with some noise), sometimes it doesn't, sometimes it will move from time to time. Sometimes you can start some motion in this case by turning the motor shaft manually. Stepper motors, like all electric motors, need a phase shift between the excitation signals to move, and without that phase shift (usually 90 deg between the A and B signals) they will never run as they should.

I think you should check the coil current setting of your motor driver. Maybe the driver is overloaded and then cuts current. You can also check the voltage across each pair of motor lines (A+ against A- and B+ against B-) with an oscilloscope. Most stepper drivers generate a PWM signal. If the motor driver is not activated and if you do not reduce current to zero when no step signal is applied (many drivers have this option) you should always see a rectangular waveform of some volts (not higher than the nominal voltage of the motor coils, usually around 2 to 6V) in the 20 to 200kHz range (check the chopping frequency specs of your driver). Maybe it accidentially gets overloaded in one of the configurations you tested.

Usually it does not matter much if you swap the (+) and (-) lines of each coils, this usually just changes the direction of rotation.

[tochuck123]

I'm using my home login name....

I didn't think I "broke" the motor.  All the test I tried I also tried on an identical motor which was working.  The other motor didn't have any problems.

Also I was using the same drive box while testing both motors.  One motor works the other (again an identical model), didn't.  I know the current setting was not too high as the motors are rated for 4.1 A/phase and the drive box was set to 2.6 A/phase.  There is a third motor I'm also using that uses the lower current setting and while I'm doing all this it was easier just to be able to use the one drive box (the lower current setting works fine on the higher rated motors).  There is a current reducing option on the drive box (cuts to 50% when there is no movement signal), I'm not sure what it is set to, but I could changing that, but I have a hard time believing that is going to make it work when it already is working for the other motor.

Anyway thanks for the suggestions.

Chuck