Z axis Control problems

Hi,

I've recently bought a RepRap Prusa i3 kit and assembled it. However, I keep running into problems with the stepper motors.
I'm running a Mendel kit with Numa 17 motors.

First, none of them would work. After digging on this site for similar problems, I modified the Configuration.h, lowered the acceleration speed and so on.
After, I tried to modify the Vref value (by turning the screw on the stepper control chip) which is supposed to be at around 0.4 - 0.5V.
I got X and Y axis to work by putting in a value of 1.5-1.6 V (maxing it out really) but Z still seems to be underpowered.

Does anyone have any advice ? I'd really appreciate it.

Check for binding in the axis. You can disconnect the couplers and see if you can easily move the z assembly up and down. It should not bind at all, and in fact you should be able to move it from either end - not just the center. If you have any binding, check the parallel if the Z bars. They need to be perfectly parallel. I've also encountered slippage like this is when one side of the axis was higher than the other so that it wasn't parallel to the bed.

First off, thanks for answering.

Now, I've taken the couplers off and tried turning the Z motors while they're entirely disconnected from any load.

At Vref = 1.5V, they oscillate a little bit when I try manual control. I'm guessing they do 1 step forth, on back, one forth and so on...

Edited 1 time(s). Last edit at 08/28/2014 10:38AM by Astra.

Can you try swapping in a different driver board, just to see if you can isolate the problem?

I don;t know your electronics setup, but I use RAMPS/Pololu drivers. I had one of my drivers fail to where the motor would go back and forth I swapped out the driver and all was well again.

The drivers are somewhat fragile. If you plug one in, or even just plug a motor in, while power is on, you can ruin the board. In my case, I plugged everything in without power, but I didn't realize that the plug was shifted on the header by 1 pin, so it was basically wired wrong. When I corrected this situation, I found the driver had been destroyed.

I try to always have a few driver boards on hand.

My electronic setup is also RAMPS/Pololu drivers.
So I swiched two driver boards but the problem persists. I also tried to control one motor of the Z axis with the driver of the Y axis, switched two wires basically, and the motor worked perfectly.

I don't believe that there's anything wrong with the physical setup and that it might be a software issue.

Edited 1 time(s). Last edit at 08/29/2014 05:41AM by Astra.

Ok, new development :

I took all of the motor wires off the board and reconnected only one of the Z axis motor connection. And it worked !!
Then I tested the second set of pins and then the other motor and everything worked fine.

After that I connected BOTH motors at the same time and then I end up with the same problem as before. So it's not a software issue after all (kinda relieved)

At this point I don't know. Maybe the voltage is too low to activate both motors at the same time, or maybe it's a current issue...

Final post, SOLVED :

The jumpers were not under the stepstick chips. The instructions in french kinda missed that las part...
Now that they are, everything is in order.

If anyone is having the same issue and found this post, that's the first thing to look for.

Good luck and have fun