X Axis Stall

Hello,

I have recently built my own CNC machine and after bits of advice from the forum its been working an absolute treat!

until...... It has just randomly started to stall whilst moving up and down the x axis and then recover shortly after. This then goes on to offsetting the x axis by anything up to 100mm. I can't seem to replicate it as it happens during different events. Which is making problem solving difficult.

I have read a few other threads on the site but its rather complicated so I may need a little 'hand holding' to get to the solution.

I'll just mention the x-axis details as this is where the problem is:
Nema 34 8.7nm stepper motor
Stepper motor driver 6.0A 80v micro stepping cw8060
UC100 Motion controller
UCCNC software
CP0-10v Break out board
480W psu 48V 10A CNC power supply (also providing power to 2*Nema 23nm Stepper motors via cwd556 5.6A drivers(y and z))

Having read a few other threads, from very basic principles - its either mechanical or electrical.
Mechanical - I am going to have my lunch and then go and remove the motor and turn the ball screw by hand to make sure that this isn't a case of mechanical interference, dirt preventing motion.

Knowing only a little about electrics - is this a torque problem? Would it be the case that the Stepper motor can't get the required current? when changing direction. Should I power this stepper from a separate PSU? If this is the case, what logic causes the x stepper to stall and not the y or z (I believe the term is called a brown out). I briefly had a multimeter on the psu tails to the cw8060 when it stalled but I didn't see any voltage drop.

All help greatly appreciated!

cheers
Andy.

How frequent does it happen? if frequent enough that you can test and be confident that you should see the problem (e.g. repeat a x-traverse 100 times in g-code), then why not power down disconnect the Y/Z axis and test again - if the problem remains it's not brown-out of the main supply, and you can tick that off your list.

What are your microsteps on the CW8060 set to?

I know this seems to be my particular 'bete noire', but check the wiring particularly at places that move. Make sure that all connections have the wires clamped either side so the whole thing is shake proof and that cables flex on as large a radius as possible. One wire to a stepper with an intermittent break can cause all sorts of grief.

Couple of thoughts.

First - 48V and NEMA34 motors don't really go together. The high-inductance motors need a fair bit of volts to get them going. It's possible that things have tightened up a bit or moved slightly out of aligment since first building the machine, so more friction, so more likelihood of stalling? Does it still happen if you reduce acceleration and max speed? Try low values just for testing purposes.

Second - and possibly linked to first. Sounds like you are using a switch-mode power supply. These are really not ideal for stepper motors. Steppers need high pulse currents even if the average is low, and it's possible that these peak currents (possibly increased because of a bit more friction as above) are tripping the over-current limits on the PSU. Ideally, you should be looking at about 68V from a linear power supply - details and how to build are available on this site!

This going to be one of two things IMO,
#1 slippage of couplings/pulleys or friction due to mechanical wear/failure.
#2 Lose or breaking/ trapped wire

However, everything Neale mentions is correct and could very likely be a cause of trouble and most certainly will be straggling performance, so I 100% agree with him that you should up the volts for the Nema 34 and go with a toroidal type supply. But first I would try to identify the cause of this issue if it as been working ok for a lengthy time, the simplest way to check the PSU would being just running the X-axis with the other axis unpowered.

My suggestion would be to write some G-code with 1000's of short moves at full rapid speed but just long enough to let the motor reach full speed before changing direction. Zero and Mark the axis before starting the run and finish by having it come back to Zero.
If it returns to zero, then repeat but this time run the other axis at the same time, if it then drops steps then it's a power issue.!

Quote:

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Originally Posted by Neale

Couple of thoughts.

First - 48V and NEMA34 motors don't really go together. The high-inductance motors need a fair bit of volts to get them going. It's possible that things have tightened up a bit or moved slightly out of aligment since first building the machine, so more friction, so more likelihood of stalling? Does it still happen if you reduce acceleration and max speed? Try low values just for testing purposes.

Second - and possibly linked to first. Sounds like you are using a switch-mode power supply. These are really not ideal for stepper motors. Steppers need high pulse currents even if the average is low, and it's possible that these peak currents (possibly increased because of a bit more friction as above) are tripping the over-current limits on the PSU. Ideally, you should be looking at about 68V from a linear power supply - details and how to build are available on this site!

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I was disappointed with my mill Z 34 stepper max speed on 60vdc. Accel was quick but rpm lacking.
I've recently swapped driver to a dm860t https://www.omc-stepperonline.com/download/DM860T.pdf and powering it off a new 80vdc.
Haven't got into fully testing yet.

Quote:

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Originally Posted by dazp1976

I was disappointed with my mill Z 34 stepper max speed on 60vdc. Accel was quick but rpm lacking.
I've recently swapped driver to a dm860t https://www.omc-stepperonline.com/download/DM860T.pdf and powering it off a new 80vdc.
Haven't got into fully testing yet.

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You won't see a massive difference in speed with only 20V difference, if you want real speed with large 34 motors then you really need mains-powered drives. These give high speed and torque.

Quote:

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Originally Posted by JAZZCNC

You won't see a massive difference in speed with only 20V difference, if you want real speed with large 34 motors then you really need mains-powered drives. These give high speed and torque.

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Probarbly not. Maybe an extra 400mm/min ish. Not much, but there'll be a lesser risk of skips/stalls if left at the present settings.
I was looking at the Leadshine DM2282 but..... For around another £100 I could get a basic 1kw AC servo set instead.
That's my future route so I'll make the most of what I've got until then.

Quote:

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Originally Posted by dazp1976

I was looking at the Leadshine DM2282 but..... For around another £100 I could get a basic 1kw AC servo set instead.
That's my future route so I'll make the most of what I've got until then.

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What mill have you got that you think a 1Kw servo is a correct choice.? I've got an Hurco BM40M milling machine that weighs 8 tons and is the size of a transit van that is only fit with 1.5Kw servos.. . Remember bigger doesn't; always make it better, often just more expensive with lower performance than a correctly sized motor.

Hello, Thank you for the replies.

So having read the suggestions and getting some time to address the issue:

Firstly, no mechanical problems with the machine, took the stepper motors off and checked it all turns freely. It's not mechanical wear/failure.
Secondly, no loose wires. All checked for continuity (as much as I can - obviously I can't check inside the stepper motor).

Wrote simple G-Code file to motor x axis back and forth around 100 times. No problems. On returning to a complicated spiral cutting pattern creates a sporadic stall again.

I hear the suggestions regarding power supply, I'm on a starters learning curve at the moment. I have obtained a 48V 600W 12A supply and have changed to over.

Doddy, you mentioned what are my micro steps on my cw8060 Set to: 4.28A, Half Current, 1/10th microstep. Am I limiting current thus causing the problem?

onwards..........

Quote:

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Originally Posted by AndyW

Doddy, you mentioned what are my micro steps on my cw8060 Set to: 4.28A, Half Current, 1/10th microstep. Am I limiting current thus causing the problem?

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No, you are not limiting current, Half current only applies to when the motor is at a standstill, it then drops to half current after a period of time to reduce motor heating.

You said before that the machine has been working fine so I very much doubt it's a motor tuning issue which is one of the reasons for asking about the Micro steps.
However, if you have changed the motor tuning then this would cause missed steps if you have the motors over-tuned.

So if you are 100% sure it's not mechanical or electrical then you could lower the motor tuning and it will most likely go away but in my opinion, but seeing as it was working fine before, this could just mask the real issue.

Give more info on the motor tuning and the controller being used so it will give us a better idea if you are over tuning or not.