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Topic: Unipolar stepper motor and ½ steps (Read 363 times) previous topic - next topic

Johan_Ha

Jan 09, 2018, 09:56 am Last Edit: Jan 09, 2018, 09:58 am by Johan_Ha
Here's someone testing a unipolar 5 wire stepper motor.

Am I on right track if I say this is whole steps? A 5 wire unipolar stepper motor needs 4 datapins and having each go high subsequently while the other three go low, will perform this action seen in the video, right? (Going high means opening a corresponding transistor, which will activate corresponding coil in the stepper motor.)

But most code for unipolar show a pattern of 8 steps, not 4:


     0   1   2   3   4   5   6   7
D0   HI  HI  LO  LO  LO  LO  LO  HI
D1   LO  HI  HI  HI  LO  LO  LO  LO
D2   LO  LO  LO  HI  HI  HI  LO  LO
D3   LO  LO  LO  LO  LO  HI  HI  HI


So the even steps would be the whole steps, while the odd steps would be the added half steps. If I'm on right track, do all 5 wire stepper motors behave like this? Or are there motors uncapable of handling the half steps? Or are there motors requiring this half step pattern?

I haven't found confirmation for my assumptions. I'm working on hijacking the stepper motors on an old typewriter to turn it into a plotter and the motors are 5 wire unipolar. I'll be actually hijacking the "drivers", too, which are two IC:s with 7 darlingtons and 7 diodes in each. Since it will be a plotter, I'm most interested in achieving a good resolution by having half stepping or even micro stepping work.
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jremington

Quote
So the even steps would be the whole steps, while the odd steps would be the added half steps.
Correct. 5 wire steppers can all do this, but they can't do microstepping.

Johan_Ha

If I set D0 high and all others low, the motor takes one position. Then if I set D1 high and all others low, the motor rotates to next whole step. But if I leave D0 at high while D1 goes high, the motor takes the half step inbetween. What prevents from introducing microstepping here? Can't D1 go halfway high? Or is 5 wire unipolar so ancient technique that nobody bothers to develop microstepping drivers for them?
____________________

If you ask for help and write 'u' instead of 'you' because you think it's convenient, I will write 'no' instead of 'yes'. For same reasons.

jremington

#3
Jan 09, 2018, 09:18 pm Last Edit: Jan 09, 2018, 09:18 pm by jremington
Hardly anyone bothers with unipolar motors these days; they are so inefficient.

Daenerys

There exist microstepping unipolar drives.

http://www.allegromicro.com/en/Products/Sanken-Products/Sanken-ICs/Sanken-Motor-Driver-ICs/Sanken-Stepper-Motor-Unipolar-Driver-ICs.aspx



But I think you would be better off ditching the 5-wire motors and just buying appropriate motors.
Then you have a wide choice of microstepping bipolar drivers to use.

A very wide choice.  And they are cheap as chips.

MarkT

If I set D0 high and all others low, the motor takes one position. Then if I set D1 high and all others low, the motor rotates to next whole step. But if I leave D0 at high while D1 goes high, the motor takes the half step inbetween. What prevents from introducing microstepping here? Can't D1 go halfway high? Or is 5 wire unipolar so ancient technique that nobody bothers to develop microstepping drivers for them?
Yes, ancient, inefficient use of copper (much more expensive than the electronics these days!)
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