I had a the same misery up until about 30 minutes ago. I read on a RepRap forum that you need to really keep the Arduino Stepper drivers cool or you get print shifting (as the drivers screw up so much internal logic when they overheat!), and someone suggests a house fan pointing at the Arduiono directly. I did this right in the middle of one of my miserable "shifting" prints, and after I opened the Arduino box and pointed the fan at it for about 1 minute, the print started to print correctly. I jumped for joy and ran around the house.
My 5 year old came to take a look and kicked the cord on the fan, and the behavior of "shifting" cam back! I plugged the fan back in and it magically finished the print. See attached picture and you can see the change and also the moment the fan got kicked out. I could attach about a dozen failed prints, but now that I have this solved, my mood is elevated and I am going out for dinner.
Also, I have read and talked to many about how much power to put into the steppers via the little analog pot. You want to drive at the highest voltage you can get, but also back off before their make that clicking sound. They should just whine a bit, and then you have it at the sweet spot. With my steppers, this feels like about 75% of the total rotation of the pots for me to get max power, before going to far.
Gordon's printer uses a nice stepper actually. I looked into it. It has 0.45Nm of torque and uses 1 amp, and that is pretty good ratio. So it seems these Arduino drivers can only handle 1 amp, so if anyone is thinking of a new stepper for the Z-axis (if they make a heavier bed), you will most likely need a better driver for the Z-axis channel.
- These users thanked the author uprightfan for the post (total 0):