Micro Stepping a BiPolar Stepper motor

Jim Fouch

I'm quite new to the SX & SX/B but have used the Basic Stamp 2 & 2SX for a while.
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I'm interested in making a homebrew NC Drill for drilling PCBs. Being a cheap guy I'm trying to make the XY table out of old computer parts. I have a nice scanner that has agreed to be sacrificed for the better good of my enjoyment. I have managed to take control of the stepper using an L293D Double H-Bridge. I can get the movement ·down to .00328”/step but am looking to get closer to .0005”/step.
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Does anyone have any sample code that will allow me to micro-step a Bi-Polar motor using the SX?
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Thanks,
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Jim


Here is a sample of my code so far...

MotorSteps:
· Data %0000
· Data %0011
· Data %0110
· Data %1100
· Data %1001

Forward:
· INC StepIndex
· If StepIndex<5 then SendMotorCommand
· StepIndex=1 ' Rollover
· Goto SendMotorCommand
Reverse:
· Dec StepIndex
· If StepIndex>0 then SendMotorCommand
· StepIndex=4
SendMotorCommand:
· TRIS_B = %11110000 ' Setup Outputs
· Read MotorSteps + StepIndex, RB
· Pauseus 1800
Return
RelaxMotor:
· TRIS_B = %11110000
· RB=%0000
Return
Start:
For J=1 to 100
· For I=1 to 50
··· For Counter=1 to 5
····· Gosub Forward
··· Next
··· pause 50
··· For Counter=1 to 5
····· Gosub Reverse
··· next
··· Gosub RelaxMotor

··· Pause 50
· next ' I
· Pause 60000
next ' J
End

PJMonty

Jim,

First, the steppers you pulled from the scanner are going to be very weak. Depending on how much weight, mass, and friction is involved in the X-Y table, they could easily be too small for the job. Second, probably everything you want to know about do it yourself micro-stepping can be found here:

www.fromorbit.com/projects/picstep/index.php

The code is for the PIC, but it's all open source source (as is the hardware design) so you can go nuts with it.

Thanks, PeterM

Bean

I thing I caught is that your stepindex variable should go from 0 to 3, instead of 1 to 4 like you have it.



MotorSteps:

Data %0000
Data %0011
Data %0110
Data %1100
Data %1001



Forward:
INC StepIndex
StepIndex = StepIndex AND 3
Goto SendMotorCommand

Reverse:
Dec StepIndex
StepIndex = StepIndex AND 3

SendMotorCommand:
TRIS_B = %11110000 ' Setup Outputs
Read MotorSteps + StepIndex, RB
Pauseus 1800
Return

RelaxMotor:
TRIS_B = %11110000
RB=%0000
Return

Start:
For J=1 to 100
For I=1 to 50
For Counter=1 to 5
Gosub Forward
Next
pause 50
For Counter=1 to 5
Gosub Reverse
next
Gosub RelaxMotor

Pause 50
next ' I
Pause 60000
next ' J
End

Bean.

Jon Williams

What I do know is that you're going to need more than four steps in your sequence. If you do half-steps you'll double the resolution. To get better than that, you have to control the power applied to the two phase coils that are affecting the armature.

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Jon Williams
Applications Engineer, Parallax
Dallas, TX· USA

Jim Fouch

Thanks for the reply. I think I'm going to try to microstep it into 16 smaller steps. Not sure if this will work, but I have a few ideas I'm going to try. I'll post my results.

Thanks,

Jim Fouch

Jon Williams

With direct on and off control (no voltage variation) you will only be able to use eight steps. Here's a couple tables from one of my BS2 programs to give you an idea.

Full Steps:

'                          __
'                        ABAB
'                       -----
Step1           DATA    %1100
Step2           DATA    %0110
Step3           DATA    %0011
Step4           DATA    %1001

Half Steps:

'                          __
'                        ABAB
'                       -----
Step1           DATA    %1000
Step2           DATA    %1100
Step3           DATA    %0100
Step4           DATA    %0110
Step5           DATA    %0010
Step6           DATA    %0011
Step7           DATA    %0001
Step8           DATA    %1001

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Jon Williams
Applications Engineer, Parallax
Dallas, TX· USA