Erratic Z axis motion

graybeardtx

I have converted my Prusa I3 clone from a Melzi control system to a RAMPS 1.4 and ATMega 2560 control system with a full graphic smart controller. I am running the Repetier firmware created with the online configurator 0.92.9. I have managed to get almost everything working correctly again with the exception of the Z axis. It seems to have a mind of it's own.

I have added the delay to STEPPER_HIGH_DELAY 1 and it has improved the repeatability but occasionaly the software position of the printhead changes according to a move command but the head does not mechanically move. The X and Y axis work fine. I have made the delay as high as 5 but that hasn't eliminated the problem.

Not sure if it is relevant but the Z axis doesn't always respond to the manual moves by the controller although the software position gets changed.

Repetier

Z axis can easily stall. Then you hear some sound but no move. Make sure jerk and acceleration and max. z feedrate is low to never block. Jerk 0.3, Acceleration 50 and max. feedrate 2 is a safe start. From there you can increase to find what your limit is.

graybeardtx

Thanks. I tried those values and it didn't have any noticeable effect. As an unscientific observation, there doesn't seem to be any stalling of the motors. It really appears that the commands are somehow being ignored.

I did a simple test - moving the Z axis up and down repeatedly to different values. It ran fine, never skipping a beat.
G21
G90
G28 xZ
G1 Z10
G1 Z5
G1 Z15
G1 Z3   
G1 Z0

When I added a single X axis move to the script, it would skip or miss a Z axis move randomly.
G21
G90
G28 xZ
G1 Z10
G1 Z5
G1 Z15
G1 X25
G1 Z3   
G1 Z0
Additionally there may be a long pause between steps.

I'm stumped.

Repetier

G28 Xz must by G28 X0 Z0
Test your endstops with M119
If z endstop is triggered in move direction, the z move will be ignored and hence no sounds will appear. This might also happen from crosstalk e.g. from x stepper.
One other reason not to move might be not being homed (not sure if it did with the wrong syntax)

graybeardtx

I corrected the G28 line. The end stops are all "off" during the moves. I wondered about the possibility of cross talk. The wires on the steppers are all 1M long so they are not cleanly separated. But because they were terminated with Molex connectors I did't want to shorten them until I got the system working.

I'm going to look again at the Z stepper driver setup.I might have it set to too many microsteps for this particular confighration.

graybeardtx

Turned out to be a defective RAMPS 1.4 card. The D2 diode looked to be fried. Not sure how that figures in but I replaced the board and it all works smoothly now.