Y axis negative direction drift. Help!

Ok. I used those EZ540 boards to set the current limit. Perhaps I am limiting the current too much?
I will look into this.
Thanks!

cncbasher wrote:

their should be no difference in cutting any size circles arc's or whatever , or works ok at one size but not at another etc ...
simply put if the cutter is moving off target path there is a reason for it , either feed rates too high or pushing the cutter through the material rather than allow the cutter to do it's work first .
or stepper is missing steps for whatever reason ...

as you are cutting in air and not material , that only leaves , mechanical issues , belts and stepper setup.

remember on arc's you have all axis moving at once and therefore drawing current from the psu at a greater rate , than if you were moving one axis at a time , so check your current settings on the stepper driver they may well be too low
or the psu cannot supply the amperage needed for all the motors at once , for example .

As cncbasher stated I would lean toward...

psu cannot supply the amperage needed for all the motors at once ,

And of course check that the drivers amp setting is correct, any chance it was accidentally changed between when you said the machine worked well and now?

This would be a good time to put a meter on the PS and check it's voltage and the amps that are being drawn with the machine working.

Rick G

Interesting. I found out my motors are rated for 2.5A. For the G540 driver, you set the current using a resistor. I checked what my current set resistor is at and it is 2.0K (I am using an EZ-G540 board to do this with a trim pot), which means I could bump this up. My guess is the combined X-Y movement of the arc is really needing a lot of power to do the job?

I plan on setting them to run at 2.5A and run that arc to see what happens.

Thoughts?

Be sure your power supply has enough amps to run all the steppers at the same time.
Most drivers have a setting to allow reduced amps when the motor is not moving, so if you have three motors and only one is moving it would require less amps than all three motors moving together.

Rick G

let us know what power supply you are using both and list the output Voltage and Amps please

48vdc 400watt power supply

ok 48v and at 400w = 8.3 Amps your motors are 2.5A per phase max , so 2 phases per motor ( coils ) that's 5A per motor , you have 3 motors so essentialy in theory they could draw 3 x 5A = 15A
but you have a max of 8.3A so your deficient in Amps by 15A - 8A = 7A Although you would not reach 15A in real use , but experience comes in too , so i'd say your a bit low on current , i'd say 10A - 12A would be about right
but more is no harm , just means you have some in reserve ...

perhaps see if you can add another power supply and supply the z axis separately or try running with the z axis disconnected totally from the power supply and see if the error in the path goes away . if it does then that's been the problem .
lack of Amps when all 3 motors are under power together .

yes this is a crude way of working it all out , but for non electronics gifted folks it's a good guide , and will get you out of trouble , without getting a headache !

48v is a good reasonable value for 3 axis modern steppers , ... again in a crude way think Volts = acceleration speed and Amps as Holding a position ( torque )

modern stepper drives control current flow ( amps ) and in doing so this limits the volts , hence why you can say have 5v steppers on a 48v power supply
so in effect control the torque and holding force , and why steppers tend to run hot as they draw more amps when stationary to hold position etc . so it's important to have the current setting within the motors limits in current ( amps)

I found out my motors are rated at 2.5A. I originally had them set to run at 2.0A. I made the change to have all motors run at 2.5A and running that arc program shows a vast improvement. I can do about 4-5 passes with little drift, however if I do about 8 passes I am seeing about a tool width drift.

Originally, I had about 2 tool width drift when I ran about 2-3 passes. So this boils down to power requirements. I am assuming the driver (G540) and LinuxCnc are talking correctly and sending the right signals down the line, its just that the steppers can not keep up. It is interesting because for 90% of other stuff I have done I have not had this problem. At least we are on to the problem! Thanks!

So, it looks like I would need to upgrade the power supply?

cncbasher wrote:

ok 48v and at 400w = 8.3 Amps your motors are 2.5A per phase max , so 2 phases per motor ( coils ) that's 5A per motor , you have 3 motors so essentialy in theory they could draw 3 x 5A = 15A
but you have a max of 8.3A so your deficient in Amps by 15A - 8A = 7A Although you would not reach 15A in real use , but experience comes in too , so i'd say your a bit low on current , i'd say 10A - 12A would be about right
but more is no harm , just means you have some in reserve ...

perhaps see if you can add another power supply and supply the z axis separately or try running with the z axis disconnected totally from the power supply and see if the error in the path goes away . if it does then that's been the problem .
lack of Amps when all 3 motors are under power together .

yes this is a crude way of working it all out , but for non electronics gifted folks it's a good guide , and will get you out of trouble , without getting a headache !

48v is a good reasonable value for 3 axis modern steppers , ... again in a crude way think Volts = acceleration speed and Amps as Holding a position ( torque )

modern stepper drives control current flow ( amps ) and in doing so this limits the volts , hence why you can say have 5v steppers on a 48v power supply
so in effect control the torque and holding force , and why steppers tend to run hot as they draw more amps when stationary to hold position etc . so it's important to have the current setting within the motors limits in current ( amps)

I would follow cncbasher's advice first...

perhaps see if you can add another power supply and supply the z axis separately or try running with the z axis disconnected totally from the power supply and see if the error in the path goes away . if it does then that's been the problem .
lack of Amps when all 3 motors are under power together .

Remember not to plug or unplug any cables with the power on.

Rick G

i'm glad you are making progress .. the main reason you are having this problem is that you are moving all 3 axis at the same time within a small period of time , and that the stepper driver does not have time to recover before the next move
so it ends up struggling to keep and gives you missed steps , with all the small stops , and as I said earlier the motors draw more current when stationary .

this is also one reason where simple old fashioned power supplys are preferred to run steppers ( transformer , rectifier and capacitor only ) , rather than the more modern switch mode ones , the old ones don't run out of steam !

I would fit another 48v power supply just for the z axis of say 7 - 8A , 10A ones are popular , having a excess of available current is fine