Very good suggestion. This should indicate if its hardware or software. The code to turn FakeServo ON is “the answer to the ultimate question of life, the universe and everything.”
If it fails with FakeServo ON then we will probably need to see your gcode file and/or WebControl logs to find the problem as its almost certainly software. Don’t bother reading further.
If it works with FakeServo ON:
Turn off FakeServo and run Actions → Test motor/encoder and post results.
If Test motor/encoder is OK then:
Make sure FakeServo is OFF and move the Home position so that the piece is cut somewhere else on the workspace. You could also try physically switching the motors from left to right to see if problem gets mirrored. This could identify a motor power overload condition specific to the cut position.
Beyond that you could try basic process of elimination for USB. These are all edge cases as it sound like a reproducible rather than intermittent problem.
- Use a different shorter USB cable - motor power draw may reduce USB signal strength on the stock long cable.
- Tape down the USB cable, with a little bit of slack, on both ends - Could be a specific vibration causing lose connection.
- Remove all other USB devices connected to device that is running Webcontrol - If using RaspberryPi with WiFi Dongle and Wireless Keyboard/Mouse you could be maxing its power supply. Use at least 2A power for RaspberryPI.
- Plug USB into a different port on device that is running Webcontrol - Wear could make it lose or could just be a weak soldered port.