Step 4
Now you have adjusted the pot slightly re-read the Vref voltage as in step 2 and you should see
the change in the Vref from the adjustment you made, now you should have a feel for the amount
of change in Vref in relation to the degree change of the pot. A value of between 0.4v and 0.5v is
appropriate for the Stepper Motors in you kit.
You should notice a physical change in the behaviour of the stepper motor as the Vref is
manipulated, when it is too low the stepper motor will make a noise and vibrate as if it were
moving but it will fail to move or move accuratley, if the Vref and hence current is too high the
stepper motor will move in jerky overly highly torquey manner ( it will seem unnecessarily
powerful for the printer) and after a certain point the motor won’t move again and will vibrate
and get very hot.
Depending upon which motors are being used more heavily when printing will depict how
warm/hot they get along with their respective heat sinks on the stepper drivers, so for example
the Extruder stepper may well be considerably hotter than the z axis stepper motor as it is
Step 3
Now we have a reading of the Vref voltage, it should be between 0.40 and 0.50v, if we wish to
adjust it we need to turn the pot slightly, if we turn it clockwise we’ll increase the current drawn
and anti clockwise we’ll reduce it. Use an insulated small slotted screwdriver to turn the pot
slightly. There is a flat side to the pot, usually this should sit at around the 10/11 O’Clock
position.
11.0 Commissioning & Calibration - Reprap Prusa Mendel Build Manual
©2012 NextDayReprap
Prusa Mendel Kit Build Manual V1.01 - 07/2012