extruder working in X | Y | Z but VERY slow in XY and chattering

Hi folks,
another problem is reoccurring with the printer. When I move the extruder in a
single axis it happily hums along a full speed. But if I issue say a G1 X15 Y15 from, say, the
centre of the bed, the extruder moves INCREDIBLY slowly, say 2mm/s, and the
motors are chattering very loudly.

The steppers are being run on DRV8825s, wound up to ~1.6A, about 60% of the max
of the steppers.They are set to 1/8 usteps. The Z steppers are running on seperate
drivers to avoid the problems I was having with the Z steppers seemingly being
underpowered.

Below is the what I think is the relevant code from the configuration.h. It all seems to
make sense and no embarassing mistakes seem to be there.

Oh, I know the Z feedrate being 4mm/s is slow but when it was above 5 the steppers
were playing up and 4mm/s at the end of the day does the job.


Many thanks,
Andrew

#define NUM_AXIS 4 // The axis order in all axis related arrays is X, Y, Z, E
#define HOMING_FEEDRATE {50*60, 50*60, 4*60, 0} //

#define DEFAULT_AXIS_STEPS_PER_UNIT {80,80,4000,107*8} //
#define DEFAULT_MAX_FEEDRATE {150, 150, 4, 25} //
#define DEFAULT_MAX_ACCELERATION {9000,9000,50,10000} //
#define DEFAULT_ACCELERATION 3000 //
#define DEFAULT_RETRACT_ACCELERATION 3000 //

Maybe the power supply cannot handle all three at once.

I doubt, correction, hope it isn't a psu issue.
It is a 33a psu with only the steppers and electronics plugged in.


Andrew

Do you have the same issue when you send a G1 X15 Y15 F3000?

---

Triffid Hunter's Calibration Guide

--> X <-- Drill for new Monitor

Most important Gcode.

I've heard there are RAMPS boards, were the microstepping jumpers had no influence. The pins are bridged under the pin header!
If that's the case with your board, your extruder is running 1/32 .
IMHO it doesn't make sense to run the extruder with 1/8, you want a smooth_as_can_be filament feed to avoid blobs and other ugly things.
-Olaf

PS: With standard M5 lead screws I would reduce the Z-feedrate even lower to "3".

Edited 1 time(s). Last edit at 10/14/2015 04:10AM by o_lampe.

Hi folks,
haven't yet tried specifiying the F value in the G1. Assumed the default values
would carry through and be sufficient. Will give it a go though.

Olaf, I'm only running in 1/8 step currently as I'm testing on what had been reliable
values. Then I'm going to start bumping the ustep back up to 1/32. Maybe I'll
just jump straight back upto 1/32 ustep to save some time.
Given the RAMPS boards I have are from eBay, that purveyor of "quality" components,
I might have to check them under a scope.

Many thanks,
Andrew

If you've changed to 1/8 without changing the steps/mm, the stepper is forced to accelerate and run 4x faster. OTOH, the code you showed, indicates 1/16 steps
-Olaf

Olaf,
I forget to include my steppers are 0.9° Beastie's.
I've changed everything to 1/32 as you suggested and just
need time to test it. Oh, I double check the numbers on
the reprap calculator page each time I play with them
but I'll check the numbers again to be safe.


Andrew

Olaf,
I just remembered why I had the microstep set to 1/8.
There was an article on the myths of microstepping and it
had a table showing the drop off in torque for various levels
of micro stepping. The reduction appeared to be non linear.

The other problem the article discussed was that if the micro
steps were too small then insufficient torque would be
generated on a step command and 2 or more step commands
would be needed to get a stepper to move.

I added that all up and decided that 1/32 was why the z steppers
were freaking out, so dropped them and the others to 1/8.


Andrew

Yes, and Elvis is alive and we never landed on the Moon

This stepper torque article is a piece of BS.
We even have 1/256 microstepping drivers. They must be weak as a butterfly
-Olaf

That is the problem with so much of the material available to read.
What is, as you point out, BS and what is realistic?

I really must invest in that Olfactory Emission Circuit for the laptop.

Thanks Olaf,


Andrew

Microstepping: Myths and Realities