Steps per unit, hardware broken?

I'm starting go crazy here so I'll try my best to explain the problem. Starting to think my hardware is broken...

After calibrating the printer with my digital calipers I came up with the following settings.
These setting seem to be very good, the 10mm test cube is 9,86mm high.

Z axis settings:
steps per unit = 2024
feedrate = 1.9

Here comes the crazy part.
Sometimes I get squashed prints because the z axis only goes up half the distance. When I tell it to go up 10mm it only goes 5mm up.
Using g-code commands I change the settings: steps per unit 4048 / feedrate 0.9. Now the z axis moves 10mm like it should.

Put the same settings (4048 / 0.9) in the firmware and upload, now the z axis moves 20mm instead of 10mm!?
So I use g-codes again to set it back to 2024 / 1.9, now the z axis moves 10mm like it should.

Put the settings in the firmware (2024 / 1.9) and upload, z axis now moves 5mm instead of 10mm!


I have no clue on how or why the printer is doing this. Sometime the printer works fine but other times the z axis only goes up half the distance, the other axis work fine.
One more thing that might help, the printer doesn't always want to move in the negative direction on any axis when I tell it to via pronterface. Only after going into the positive direct once it will go into the negative direction once.

I'm using a megatronics v3 with Marling firmware.

Edited 1 time(s). Last edit at 09/20/2014 11:37AM by cyberfly.

is it possible it's getting the request twice? which is why it's double?

Hi,
I'm using Marlin on my own build Ordbot Hadron.

1)
After switching on, Marlin uses the current postion as 0/0/0 point. In the options by default of Marlin it doesn't allow moves to negative axis position.
You can change this by changing the _MIN_POS values:
// Travel limits after homing
#define X_MAX_POS 210
#define X_MIN_POS 0
#define Y_MAX_POS 205
#define Y_MIN_POS 0
#define Z_MAX_POS 134
#define Z_MIN_POS 0

But generally you should do first a homing to your printers reference point. So it travels to the endstops of your printer and sets the 0/0/0 position there.

2)
If a axis does not travel the amount of steps as needed (if calibrated) may be:
a) the current for the stepper motor is to low
b) the travel speed is to high and resistance of mechanic blocks the stepper motor
c) the current for the stepper motor is to high and the driver runs into overhead protection

One part of the calibration is, to find out the maximum speeds your hardware can do. If your feedrate is too high, you will here a buzzing sound and the axis doesn't move.

BR
Peter

Thanks for the tip!

Homing all axis before printing seems to do the trick.

Edited 2 time(s). Last edit at 10/03/2014 10:16AM by cyberfly.