I have recently finished putting together a prusa mendel i2. I get motor jitter(z axis) when both are connected to ramps but with one connected it moves fine. I am using a 12v 20a power supply. My question is, is it a power, ramps or motor issue? It is very frustrating. Any help will be very appreciated.

Thanks,

Keith

Are the Z axis motors connected in parallel or series? If in parallel, it's a power issue and you need to up the vref.

Thanks a lot for the info. They are in parallel. My motors are rated at .6 amps. How do I set the amps correctly on the potentiometer? Also is there a way to check the current with a multimeter?

Thanks again.

Here's the reprap wiki page for a4988 pololus. Make sure your drivers are pololus and not stepsticks, though, as the vref will be different.

Basically, plug your board into your PC and check the voltage on the board with positive on the pot and negative on one of the negative terminals on the RAMPS.