Prusa i3 Z motor problem

[Alex_M]

When I manually jog the Z motors from my computer they work fine, but when i press home or ask it to start a print I only get the noise and no movement. I have tried turning the screw on the driver in every way possible but still no movement. Please help. Thank you

[printbus]

As mentioned in the chat box, try slowing down the Z-axis feedrate. You're likely trying to step the motors faster than they can actually move.

[Alex_M]

Thank you i will try it in the morning. what line would this be in marlin

[Mjolinor]

It would not be in the firmware yet. You need to find a figure that works using G codes direct from the command line.

[printbus]

You could start by just experimenting with the z-axis movement speed in your slicer. The printer will move at the slower of either the slicer setting or the limit in Marlin.

What kind of printer is this, or at least what kind of z-axis drive does it have? I know MakerFarm printers with 5mm threaded rods for the z-axis can't be driven faster than 2 or maybe 3 mm/sec. I've seen slicers default to settings a lot higher than that.

The Marlin feed rate limits are in the DEFAULT_MAX_FEEDRATE parameter, with z-axis being the third value in the matrix. The last revised Marlin github baseline I looked at had a default value of 5 mm/sec on Z.

[Alex_M]

It is a Prusa I3 With the 5mm Threaded rod. I have #define DEFAULT_AXIS_STEPS_PER_UNIT {78.7402,78.7402,200.0*8/3,760*1.1}// default steps per unit for Ultimaker
#define DEFAULT_MAX_FEEDRATE {500, 500, 5, 25}// (mm/sec)
#define DEFAULT_MAX_ACCELERATION {9000,9000,100,10000}// X, Y, Z, E maximum start speed foraccelerated moves. E default values are good for Skeinforge 40+, for olderversions raise them a lot.

[printbus]

It is a Prusa I3 With the 5mm Threaded rod. I have...
#define DEFAULT_MAX_FEEDRATE {500, 500, 5, 25}// (mm/sec)...

That value of 5 might be high, but like Mjolinor said, don't mess with the firmware yet. Find the setting for z-axis movement speed in the slicer and experiment with it. A number of factors come into play here, including the stepper driver current limit setting, the weight of the carriage that the z-motors would lift, acceleration, and moving up vs. moving down.