6 Wire Motors PDF Print E-mail

Ok I have some 6 wire steppers, what next?


Match Motor Type to Drive Electronics  

Six wire stepper motors can be run with either Unipolar or Bipolar driver electonics.

Which way is best, Unipolar or Bipolar?  

 Most cases, the maximimum performance of a 6 wire motor can be achieved wired as bipolar half coil, with unipolar second as those configurations minimize coil inductance, the result is better high step rate performance. Shreading the total cost/performance options (i.e. enter the confusion)  High speed torque increases as the ratio of the motor power supply to coil voltage increases. If your motor coil is rated 3V it will perform better with a 30V power supply than a 12V power supply. (If you want to understand that more, there is an excellent paper on Geckodrives website.) Bipolar drivers are more expensive, especially as the current and voltage increases. With that consideration, a Unipolar driver that is capable of higher voltage motor power supply, may infact perfrom better than a bipolar driver with a lower voltage power supply.
The driver has to be capable of adequately powering the motor. As an example, driver electronics that have a maximum current rating of 1A would not be a good match with a motor that is rated at 3.2A. A significant percentage of the time, maximum current rating is the determining factor only second to motor type. A little under powered drive is ok, but do it only for cost or already have reasons. i.e. a number of people run the 2.8A stepper motors with 2.5A drives. 

Current rating confusion 

The motor plate say it's rated at 1A. That is the unipolar coil rating, what you set your driver max current when running it unipolar or bipolar 1/2 coil. Bipolar full coil (series) rating will be .707 the unipolar rating.

Voltage Rating 

 A coil voltage rating just relates to the coil resistance and current maximum, you can use (and should) higher voltage power supplies for the motors and limiting the current to the coil maximum current rating via driver electonics.

Wiring 

Impact of Step Size 

Full step has the most hold and pull out torque. But also suffers the most from mechanical resonance.  Practically speaking, it's nearly never used in CNC applications because of the need for rapid movement.  1/2 Step has excellent torque capability, and much improved mechanical resonance effects.   Impirically I've settled on quarter stepping because it has minimal to no motor resonance, and it doesn't demand a fast PC. 

Then comes microstepping, i.e. quarter step, eighth, tenth and so on. Step size is a debatable point and depends on application. As you go down in step size, your available power goes down also. But to counter that as you go down in step size the action becomes smoother and the problem of motor resonance goes down also, which is a speed limiting factor. 

A factor that many don't realize until it's too late is the impact of microstepping verses the PC's capability.   If you buy a microstepping drive that only does 1/10th microstep, the PC will need to generate a pulse stream at a faster rate than say a drive that does quarter stepping.  For example for a .1" pitch screw (10 TPI single start) to move linearly at 100 IPM needs a pulse rate of 33khz for a 1/10th microstep drive.  That same screw with a quarterstep drive needs a pulse rate of 13khz.  If you are using a dated computer, it may not be possible to get the rapids rates you desire if you choose to fine of microstep size.

Performance

See this video on the implications of driving a 6 wire motor:  http://pminmo.com/which-stepper-motor

In Summary

Match motor to drive type unipolar vs bipolar, make sure the driver can supply the current your motor is rated at, rule of thumb to get the most out of your motor the higher the voltage rating, the higher the faster it should be able to step, which means current limiting.  Full vs half vs microstepping becomes specific to the application.

 
 
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