As I calibrated my printer, I observed a kinda strange issue. While moving my Z axis up and down repeatedly, I measured different lengths. Up and Up gave me exact 10mm. Down and down another 10mm. But sometimes it measured only 9.8mm. So, what was wrong?
After some testing, I figured out that it only happens during a direction change. This means I can lift my Z-axis by 10mm as often as I want, but the next time I lower the Z-axis, it will measure 9.8mm.
For a system with gears, I expected this because gears need to have some space to fit inside one another. Therefore, the space will cause such behavior. But with a direct-driven Z-axis, this was unexpected.
I don’t think that this was because the screw was worn due to the weight of the X-axis, which is hanging on it with some pressure. So, for me, the current drop during direction change could be a reason.
However, the Marlin firmware can handle this if it’s not a mechanical issue. Search for BACKLASH_COMPENSATION to enable it.