Lowrider 2 get out of track

LowRider CNC Troubleshooting
21

I kept thinking about this and making a change and so far so good. Remove the 3 jumpers from the Z motors and they were in “full step” then change the value in marlin to fit that. Without the jumpers the value for Z is 160 mm / min. With that, a precision more than desired is reached. I leave this comment in case it helps someone
steps_per_mm = (steps_per_motor_turn * microsteps_of_motor_driver) / rod_step = (200*1)/1.25 = 160

#define DEFAULT_AXIS_STEPS_PER_UNIT { 160, 160, 160, 160 }

/**

  • Default Max Feed Rate (mm/s)
  • Override with M203
  •                                  X, Y, Z, E0 [, E1[, E2[, E3[, E4[, E5]]]]]

*/
#define DEFAULT_MAX_FEEDRATE { 120, 120, 16, 25 }

Change to 16 maxfeedrate in Z (960 mm/min)

22

I’m not sure how full steps vs. micro steps will be impacted here. That will certainly reduce the effort on the cpu, because it isn’t flipping that switch as much. But I am thinking of another affect.

Here is the story, as I understand it. Stepper drivers are trying to send a constant current. They are supplied with a constant voltage. They turn the voltage on and off to get the current they want to flow through a coil. When the motor is stopped, there isn’t much resistance, and the driver may be “on” for only 50% of the time.

When the motor starts moving, the inductance in the motor starts fighting the current, which means the constant input voltage has a harder time pushing current. The driver then is “on” for longer. At some speed, it reaches 100%. At any speed higher than that, the input voltage goes completely into the coil, and it isn’t enough voltage to meet the current set point, and the current goes down.

The motor torque is proportional to the current, so they start losing torque, even though they are going at a high speed.

None of that has to do with microstepping. It is completely a factor of the input voltage, the speed the motor is spinning, and the inductance of the motor.

Microstepping is just sending part of the current through one coil, and another part through the other to try to drive the stepper to a state in between whole steps. It may be a little weaker on the partial steps, and removing those might help you in this case. Maybe that is the result you are seeing.

I also should mention that with a leadscrew, the motor turns much slower, so a 12V PSU gives you lots of room to move pretty quick before saturating.