Motors Jitter and even Reverse at low speed

Hi All,

First let me say I am new to CNC and EMC2.

I have built and installed a HobbyCNC Pro controller board and I am using the #23-205-DS8 motors from HobbyCNC. I have a system with swappable Hard drives and can run the system from Windows XP SP3 or Ubuntu installed from the Live CD.

Under Windows using KCAM the motors run smooth and have lots of torch at low speed and smoothly creep along when very low feed rates. However, running under Ubuntu and EMC2 the motors jitter and low speed and often jump back and forth between directions. At higher feed rates they seem to run fine until the feed rate reaches a point where they seem to simply lock up. The feed rates are not unrealistic. A feed rate of a half inch per minute cause the issues at low speed. A feed rate at 5 inches per minute cause the motors to lock up. The motors run fine under Windows/KCAM at these same feed rates.

I suspect the issue to be pulse timing but how can I find out short of using an osciiscope tide to the motor wiring? Does anyone know what these motors require for pulse timing/width?

Lastly, where I set the maximum Jog Speed and Maximum Voloscitiy settings so I don't have to keep adjusting the sliders on the Axis GUI panel under the Home and Jog controls.

Thank you for your aid