Ignore the g-code errors, those commands are indeed not supported by GRBL, but they don't change anything anyway.
You probably have GRBL set up with the wrong steps-per-mm value for your steppers and driver microstepping setting. You need to know:
- stepper motor: number of steps per revolution (200 or 400 steps/rev);
- driver setting: number of microsteps per step (2x, 8x, 16x...);
- pulley: number of teeth;
- belt: pitch (mm);
If you're using the stock pulleys and belt, the pulley has 18 teeth and the belt pitch is 0.08", or 2.032 mm. If you're using grblShield, microstepping is probably 8x; with Pololu A4988 drivers, it can be set to 16x, which I recommend.
Many stepper motors use a numbering scheme like this example:42BYGHM809
, which reads:
- 42: motor width in mm; 42 mm is NEMA17;
- BYGH: appears to mean hybrid stepper motor (always the same four letters);
- M: M indicates 400 steps/rev (0.9 degree/step); W or no fifth letter means 200 steps/rev (1.8 degree/step);
- 8: motor length (larger is bigger); for NEMA17, 6 means 40 mm and 8 means 48 mm;
- 09: winding type and current (generally, larger number means lower impedance and higher current); for this series, 09 means bipolar, 1.7 A or so.
In brief, BYGH and BYGHW are 200 steps/rev, BYGHM is 400 steps/rev.
TL;DR version: you probably need to double the value of the $0 and $1 GRBL parameters.