Taking info from your related post on our forums (
http://www.pmdx.com/PMDX-Forums/index.php?topic=266.0) - Is this like a glue extruder, where the motor is always going to spin one direction to apply glue? If so, make sure to disable "rollover" as in step (1) below. It should be disabled by default, but check to make sure. If rollover is enabled and you issue a "G0A30" followed by "G0A300", the 2nd move will be backwards through 0 degrees to 300 (actually -60 degrees).
I'm at home and don't have a motor to verify this with, but have you tried this:
(1) Go to the "Configure" menu and select "Mach". On the "General" tab in the lower right corner make sure the "Rollover A" box in un-checked.
(2) I tried these motor tuning parameters:
- set your motor driver for 1/8th step (1600 steps/rev)
- In Mach, set "steps/unit" to 4.444 (i.e. 1600/360 = 4.444 steps/degree)
- set velocity to 21600 units/minute (60 RPM * 360 degrees/rev, just a number I pulled out of thin air, change this for whatever a realistic velocity is for your machine)
- set acceleration to 500 units/sec^2 (again, a number I pulled out of thin air)
For me, entering a "G0A30" in the MDI box results in the SmartBOB generating 133 step pulses, which is (30/360)*1600 or as close to 30 degrees as you can get with 1/8 step resolution. Try this (with realistic velocity and accel params) and tell me what you get.
[EDIT] If you don't get the expected results, in addition to telling us how far the motor actually moved, also tell us which version of Mach4 and the SmartBOB plug-in you are running (both are available on the SmartBOB configuration dialog or the SmartBOB diagnostics dialog (go to the "Diagnostics" menu and select "PMDX SmartBOB").
Bob