How to keep stepper motors active

[Hans2]

I have been able to print my first print successfully on my Prusa Delta Rostock 3d printer G2s, using the PLA which was delivered with the printer. Now I was trying to print the same item with ABS, but failed. I think my calibration is not good enough.
I can move the print head around and measure the distance to the print bed. But the stepper motors are switched of after a short while, causing the print head to go down some distance because the stepper motors doesn't keep the print head where it is supposed to be. How can I instruct the printer to keep the stepper motors active so that the print head is always kept at the correct location?

[Mark]

try this link:
http://www.geeetech.com/forum/viewtopic ... 519#p28519