There is a possibility that Marlin introduces backlash and skipped steps.
Because my printed parts suffer from backlash (oval circles) and ripples (skipped steps which catch up later) I investigated the movement of my printer. I attached a long pen to the axis of my X-motor to be able to clearly see all microsteps and removed the belt to have no load.
Then I ran [attachment 84410 test-steps.gcode] which rotates the motor by one microstep (0.0125mm @ 80steps/mm), waits a second and moves a step again 32 times total. Then the direction reverses. The result can be seen in the figure [attachment 84415 backlash.jpg]. The motor does not rotate for each 5 steps and catches up at the 6th step. The same occurs in backward direction and a backlash of 5 steps (0.0625mm).
Then I ran another backlash test [attachment 84411 test-hyst.gcode] which rotates the motor by 5 steps back and forth a few times. This time I did not use single step commands but a single move command for these 5 steps. No movement of the motor can be observed.
I tried different stepper drivers (a4988, drv8825, tmc2100), different currents and two versions of Marlin (RC4 RC7). All exhibited the two problems.
Finally I hooked up the motor to an isolated driver on a breadboard. The driver was controlled by a Arduino UNO and a simple self written custom program: A sequence of LOW-HIGH signals for the STEP pin and a LOW or HIGH for the DIR pin allowed to reproduce the two gcode files. Now NO skipped steps and NO backlash was observed for all three drivers.
The only explanation is, that either my Chinese GT2560 board or Marlin cause these two problems. Is Marlin maybe limited in resolution? Are these internal rounding errors? Or am I doing a mistake somewhere?
Has anybody experienced this before? Could somebody try the two files? You maybe have to change the numeric values if your steps/mm is not 80.
Because my printed parts suffer from backlash (oval circles) and ripples (skipped steps which catch up later) I investigated the movement of my printer. I attached a long pen to the axis of my X-motor to be able to clearly see all microsteps and removed the belt to have no load.
Then I ran [attachment 84410 test-steps.gcode] which rotates the motor by one microstep (0.0125mm @ 80steps/mm), waits a second and moves a step again 32 times total. Then the direction reverses. The result can be seen in the figure [attachment 84415 backlash.jpg]. The motor does not rotate for each 5 steps and catches up at the 6th step. The same occurs in backward direction and a backlash of 5 steps (0.0625mm).
Then I ran another backlash test [attachment 84411 test-hyst.gcode] which rotates the motor by 5 steps back and forth a few times. This time I did not use single step commands but a single move command for these 5 steps. No movement of the motor can be observed.
I tried different stepper drivers (a4988, drv8825, tmc2100), different currents and two versions of Marlin (RC4 RC7). All exhibited the two problems.
Finally I hooked up the motor to an isolated driver on a breadboard. The driver was controlled by a Arduino UNO and a simple self written custom program: A sequence of LOW-HIGH signals for the STEP pin and a LOW or HIGH for the DIR pin allowed to reproduce the two gcode files. Now NO skipped steps and NO backlash was observed for all three drivers.
The only explanation is, that either my Chinese GT2560 board or Marlin cause these two problems. Is Marlin maybe limited in resolution? Are these internal rounding errors? Or am I doing a mistake somewhere?
Has anybody experienced this before? Could somebody try the two files? You maybe have to change the numeric values if your steps/mm is not 80.