Steppers not moving right

I've been making really slow progress, but finally got the the stage where the Prusa is built, steppers are attached, half of the wiring is connected, my Sanguinololu (1.3a w/ Pololus) is done, the bootloader is burned and firmware (Sprinter) is uploaded. I can even connect to it with Pronterface.

Currently, I just have the X & Y steppers hooked to the Sanguinololu, and they move when when I click the +/- buttons in Pronterface, but they're very erratic. They Y will move forward, then backward even when I'm only clicking, say, +10. The X does something similar, except that it barely moves at all. Mostly it just buzzes.

I've tried adjusting the trimmers on the Pololu boards, but that only helps marginally. The power source is a 300W ATX power supply.

Any suggestions on what to try to better troubleshoot this?


Conan.

Get the ol' multimeter out and check all the things that can be checked:

Steppers (for shorts)
power supply: What voltage and amperage are you getting on your leads?
stepper drivers: what voltage and amperage are you getting when you move the motors? Does this change when you change your potentionmeter (little screw on board)?
Do your pulleys bind on the steppers? Try without any pulley/load first.

Did you modify your source at all before compiling? Do you have the endstops set up correctly (it might think it has hit the end stop already, try inverting)

I had this too, but mostly on my extruder motor. Turns out I had breaks in my wires - check all the wiriing really carefully, especially where it runs into the plugs on the board and at any terminal blocks.

Check how hot the pololu are. When they overheat they turn off. Try turning the trimmer right down and slowly increase until stepper starts moving, then go a bit more. If the trimmer is too low the stepper doesn't move, if its too high, it won't microstep correctly and will overheat.

Thanks everyone for their guidance.

The issue ended up being two-fold: 1) my power supply started to go bad and is only outputting 10.7V instead of the 12+V, and 2) I had the order of the stepper wires messed up.

So after using another power supply, testing/changing/testing/changing/testing the wire order (http://reprap.org/wiki/Stepper#Shortcut_for_finding_the_proper_wiring_sequence), and trimming the stepper driver pots, my steppers are running very smoothly.

Thanks! Now on to finishing up my printer!

Might not have been a bad power supply. Those ATX supplies generally need a load on the 5V line of half an amp or more before they really start to stabilize. And I think the more you load the 12 V line the more you need to load the 5 V line, and I have even seen some mention that the 3.3V line should be loaded as well. You need a couple high power resistors or some other load. My motors vibrated badly until I put a 12 Ohm power resistor on the 5V line, now they work nice and smooth.