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Mechanics and Construction => Mechanics and Construction => Topic started by: BANE on August 25, 2007, 08:12:30 PM

Title: Bi-polar stepping motors?
Post by: BANE on August 25, 2007, 08:12:30 PM

Does anybody know anything about bi-polar stepping motors and if they are more powerful and accurate than servos?

Most importantly, how to control them?????

Title: Re: Bi-stepping motors?
Post by: hazzer123 on August 26, 2007, 06:05:01 AM

Im assuming you mean bi-polar stepping motor. 

There are advantages and disadvantages to both.

A servo has absolute positioning system, whereas a unmodified stepper motor has only relative position (if you count the number of steps).

A stepper motor has continuous rotation, and unmodified servo has a limited range.

A servo has its drive electronics onboard, you standard stepper motor doesnt.

A servo has a larger torque/size than a stepper.

To control them check google -
here are a couple of links
http://www.piclist.com/techref/piclist/jal/DrivingBipolarStepperMotors.htm (http://www.piclist.com/techref/piclist/jal/DrivingBipolarStepperMotors.htm)
http://www.ams2000.com/pdf/step101.pdf (http://www.ams2000.com/pdf/step101.pdf)

PS - Unipolar steppers are much easier to drive.

Title: Re: Bi-stepping motors?
Post by: Ro-Bot-X on August 26, 2007, 11:32:52 AM

Quote from: hazzer123 on August 26, 2007, 06:05:01 AM

PS - Unipolar steppers are much easier to drive.

I disagree. Using a L297 and a L298N you can easily drive a bipolar stepper. You need one pin for direction (clockwise/counterclockwise), a pin for steps and optionally a pin for full_step/half_stepping from your micro to the L297.

Also bipolar steppers have a better power/weight ratio (more powerfull for the same weight).

Title: Re: Bi-stepping motors?
Post by: hazzer123 on August 26, 2007, 05:59:15 PM

hmmm it looks like you are correct :)

Ive only ever controlled stepper motors with transistors, not using any fancy driving chips, but it seems a lot neater to use one.

Title: Re: Bi-polar stepping motors?
Post by: BANE on August 26, 2007, 07:23:28 PM

Quote from: hazzer123 on August 26, 2007, 05:59:15 PM

hmmm it looks like you are correct :)

Ive only ever controlled stepper motors with transistors, not using any fancy driving chips, but it seems a lot neater to use one.

I've got a question, could you show me a diagram of the transistors you used?  I didn't know that you could do that.

Title: Re: Bi-stepping motors?
Post by: hazzer123 on August 27, 2007, 05:49:44 AM

Have a look at the right hand side of this schematic -

http://aaroncake.net/circuits/stepper.asp (http://aaroncake.net/circuits/stepper.asp)