Arduino grbl stepper motors forward and backward different distances

Using Arduino Motors, Mechanics, Power and CNC
1

Hi all, I am new here. I am running into some strange issues with my arduino project.

I have a small stepper motor CNC running off of a 9V 2A power supply. I loaded grbl 0.8c onto my arduino to move the stepper motors. The EasyDrivers to move the motors are connected to the Vin source. The EasyDrivers are all at their minimum current setting. The stepper motors that I am running are from CD drives.

I have a strange thing going on- whenever I move the Y axis positively or the X axis negatively, the steppers move the correct amount- about a centimeter. However, when the motors run the other direction, they move about 1.5 times as far as they should.

Here is some example g-code. In parenthesis are what the motors actually do:

%
M3
G21 (mm)
G00 X0.0000 Y0.0000 (nothing)

G00 X -10 (moves -10 mm)
G00 X0.0000 Y0.0000 (centers correctly)
G00 X -10 (moves -10 mm again)
G00 X0.0000 Y0.0000 (centers correctly)
G00 X -5 (moves -5 mm)
G00 X -5 (nothing)
G00 X 10 (moves about +15 mm)

M5
G00 X0.0000 Y0.0000 (centers correctly!)
M2
%

I believe that it is some sort of software issue, because the motor centers correctly in the end.

So here are the settings for my grbl.

Grbl 0.8c ['

Please help me set the movement to normal so that forward and backward move the same! thank you! for help]
$0=53.330 (x, step/mm)
$1=53.330 (y, step/mm)
$2=53.000 (z, step/mm)
$3=5 (step pulse, usec)
$4=250.000 (default feed, mm/min)
$5=500.000 (default seek, mm/min)
$6=192 (step port invert mask, int:11000000)
$7=25 (step idle delay, msec)
$8=5.000 (acceleration, mm/sec^2)
$9=0.050 (junction deviation, mm)
$10=0.100 (arc, mm/segment)
$11=25 (n-arc correction, int)
$12=3 (n-decimals, int)
$13=0 (report inches, bool)
$14=1 (auto start, bool)
$15=0 (invert step enable, bool)
$16=0 (hard limits, bool)
$17=0 (homing cycle, bool)
$18=0 (homing dir invert mask, int:00000000)
$19=25.000 (homing feed, mm/min)
$20=250.000 (homing seek, mm/min)
$21=100 (homing debounce, msec)
$22=1.000 (homing pull-off, mm)
ok


Please help me set the movement to normal so that forward and backward move the same! thank you!
2

I don't think this is the place to get specific advice on grbl.

Is there a grbl forum somewhere? Or perhaps some of the CNC forums?

...R

3

Have you tried just testing the motors with Stepper or AccelStepper libraries first?

The issue may or may not be GRBL related and this would help determine this.

4

Whoops, figured this out a while ago. The commands are absolute, not relative.

This means that "-5" then "-5" with no movement is correct, because the position is the same :stuck_out_tongue: