In some of the 3D Chameleons, the motor current might not be high enough (specifically, the older kit units.) If you have one of these units and are experiencing issues with either the selector or the extruder motors skipping, please adjust the motor current to the 1 o'clock position for both of the motor controllers in the 3D Chameleon electronics. The steps are very simple...
1) Unplug the power to the electronics and the printer. 2) Locate the two adjustment POTs on the small stepper driver boards in the electronics.
3) Rotate them to the 1 O'Clock position. By default, they'll be at the 12 O'Clock position.
4) Replace the lid and power it back up.
Here's a picture of the POTs of before and after.