Losing Z steps

what you are seeing is the difference between the capabillity of the stepper motor in real life , and mathmatics , high microstepping values and steppermotors that cannot move these extreme small amounts
the higher the microstepping the worse these results become , as a stepper motor can only move one step at a time i.e 1.2 degrees , and the electronics of the microstepper driver trying to interpolate the microsteps
which cannot be achived , however EMC can calculate the move , so therefore you build up an error over time .

reduce the z axis microsteps by 50% and you should find it better ,

high microstepping values and steppermotors that cannot move these extreme small amounts
the higher the microstepping the worse these results become , as a stepper motor can only move one step at a time i.e 1.2 degrees , and the electronics of the microstepper driver trying to interpolate the microsteps
which cannot be achived , however EMC can calculate the move , so therefore you build up an error over time .

That has not been my experience.

I beleive the G540 has fixed micro stepping as John pointed out.
However when microstepping the stepper motor has less torque. If your power is marginal you could be losing steps when microstepping.

You should go back and tune the driver if you have not done so already,(see the manual) I once tested a drive and before tuning the driver and using 10 micorsteps the shaft when forward in several uneven movements and then back a bit then completed the last microstep where it belonged. It moved much better after tuning.

Try tuning, if that does not help you may just need more power, or change your pulley/drive arrangement to give more torque.

Rick G

hazmat wrote:

The plot does show the Z tool level changing- I did some experimenting and I found that it is only losing steps in a slow (G1) move, I had set the tool speed very low (F0.1 in the G-code) and the stepper was not moving at all, while I could see the back-plot changing. I sped *up* the feed rate during cutting to F2.5, and it was able to do the entire engraving cycle without losing any Z.
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I have never lost steps (I am aware of/have evidence of) in X or Y- the only real difference is the thread pitch on the feed- 32,000 microsteps per inch on X and Y, 20,000 microsteps per inch on Z.

A couple of quick thoughts...

Did you select the current set resistor based on calculations?

Did you size the voltage power supply based on the induction calculation in the manual? The power supply voltage is determined by multiplying the square root of the motor’s inductance by 3.

Z does seem to be at a disadvantage over the X & Y axis with a higher gear ratio and having to fight gravity to move the mass. So if X & Y barely make it with 24v then Z could just be loosing steps.

You might do the Z test at the slow speeds and have some scrap wood to cut.

John

John,

I'm not familiar with the equation you gave- I chose the current based upon the motor's specifications- the motor is rated at 2.5A/phase, and I had 2.2K resistors... so I chose 2.2A. The inductance on these motors in this configuration (they are 8 wire motors, I'm running them in a series mode) is 6.6mH/phase- using your equation, the number doesn't make sense 3*((0.0066)^.5)=.24, if I use the inductance in mH, it would only be 7V. A pointer to the basis for your equation would help- I am an EE, so I won't be too intimidated by the math.

Considering the driver is current limited, I thought a good place to start was 2.2A (10% below max current for the motor). The G540 does a current reduction on standby- they don't get hot even when operating or idle- a SWAG is that they get about 10 degrees above ambient. The documentation suggests 2.5mH to 3.3mH for maximum power- I could rewire the motors, but that would drop the effective inductance per phase to 1.65mH, and I was figuring erring on the side of higher inductance would be safer.

One thing I still don't understand is that when I do a manual move at the smallest increment (0.0001) I can hear the motor moving (spindle off, of course)- that should be 2 microsteps. when I'm doing this move under the GCode at the slow rate, I can't hear the motor step at all, while I can see the back-plot showing a motion. Is there any condition that EMC would not actually drive the motor at the slow rate (I'm only changing one axis, the Z, when I notice this, so I don't think there would be any interaction with the other axes)

Actually that is from the G540 page.

This is a must read from Gecko when selecting current and voltage.

www.geckodrive.com/ark-2/support.html

John

One thing I still don't understand is that when I do a manual move at the smallest increment (0.0001) I can hear the motor moving (spindle off, of course)- that should be 2 microsteps. when I'm doing this move under the GCode at the slow rate, I can't hear the motor step at all, while I can see the back-plot showing a motion. Is there any condition that EMC would not actually drive the motor at the slow rate (I'm only changing one axis, the Z, when I notice this, so I don't think there would be any interaction with the other axes)

When you say manual move do you mean you are using the jog buttons?
In which case the jog buttons are moving the machine a small distance but not at a slow velocity.

Cannot think of any condition that EMC would not drive the motors regardless of how slow.

Have you removed your stepper motor from the axis drive and try running it with EMC witout any load?


Rick G