Stepper motors not holding on Y-Axis

[martyncnc]

I'm after some troubleshooting advice...

I've noticed recently that sometimes when I start my CNC the Y-Axis stepper motors have very little holding force... all other axes are locked solid but the Y axis (which is the gantry and has a stepper motor on each end) is easy to move by manually pushing it.

The fault doesn't always happen but seems to be getting more frequent.

One of the Y-steppers seems to be worse than the other... so one side is easy to move by hand and the other side still moves but seems to have some holding force.

The control board is suitable for running 2 drivers and steppers for one axis.

Any advice to what to check? Should I expect certain currents or voltages across stepper motor wires?

HELP!

[Dragonfly]

Holding force is a function of current through motor coils. Check the settings of the drivers.
Also, drivers usually have a DIP switch which controls whether they reduce coil current when idle (normally 50%). You can test by disabling idle hold current reduction.
And there is the 'Enable' signal to the driver which when deactivated turns completely off the voltage to the coils.

[martyncnc]

Thanks!

The dip switches have not been changed but this gives me something to start from!

Is there a way to measure the voltage at the steppers to see if it is correct?

[martyncnc]

OK, so when enabled X and Z motors have 6.0V at the ENABLED on the driver output to the motors.

Both Y motors have 5.7V for some reason but all 4 motors seem to be enabled.

Reduce coil current dip switch is set to OFF which is HALF CURRENT according to the manual. Can I damage anything by turning this ON?

[Dragonfly]

What is your machine, what rating are the motors and what kind of drivers you have?
Voltage should be measured at the power input to the driver and at the output terminals of the power supply. Because the current through the coils is being dynamically limited by internal current limiter (turned on/off with high speed) voltage reading there are not true.  6 volts is way too low if true. What is the power supply output voltage?
If idle current mode is OFF motors will produce more heat, especially if the current settings are at their max. rated value. But for a short period of time will not be a problem.
Also, check the motors holding torque by trying to rotate the motor shaft by hand. Check the tightening of the couplers that connect the motor shaft with the screw. If they have become loose they may be slipping while the motor is actually not turning.

[martyncnc]

It's just a home built machine.

I discovered my multimeter was faulty because the battery was low!

Motors are Nema23 4Nm from here... https://www.cnc4you.co.uk/Stepper-Motor-4Nm-60BYGH401-03-Nema23?search=60BYGH401-03

Driver is Digital DSP Stepper Driver 5.6A, 50V CWD556...
https://www.cnc4you.co.uk/Microstepping-Driver/Digital-DSP-Stepper-Driver-5.6Amp-50Volt-CWD556

Breakout Board...
https://www.cnc4you.co.uk/Breakout-Board-and-PSU/Breakout-board-CP0-10V-CNC-4-Axis-with-Charge-Pump

The drivers all have 48V on the output going to the motors.

The voltage across the ENA+ and ENA- from the controller is 4.7V when the machine is running and 0V when I hit the emergency stop which I presume means the motors should be enabled and holding. The X and Z axes are holding but the 2 Y axis motors can be easily moved.

Could this be a dodgy connection somewhere?

[lloydsp]

"Could this be a dodgy connection somewhere?"
-------------

It very-well could be.  What sort of connectors do you have between the driver and the motors?

It's at least a reasonable thing to explore, if there are any connectors between the two.  If not, the only things could be the connections at the driver, and the connectors at the motors. (If connectors are the issue).

Lloyd

[martyncnc]

It's shielded cable from the drivers to all the motors and at the motor end I used a push connector that crimps to the driver wire.

They aren't great tbh. If you can point me to a UK supplier of decent connectors I'd be interested.

What I really want though is a way to check motor, driver and breakout board in way where I can test each component.

I could try swapping drivers with the Z or X. I'd rather not start swapping motors, but I could. Can you get diagnostic tools for stepper motors?

[lloydsp]

I'm not in the UK, but the USA, so I can't contribute to your vendors request.

Swapping a couple of axes wouldn't be a bad experiment to try!

Lloyd

[martyncnc]

I swapped the RH Y axis driver with the X axis driver.

This did not move the problem at the motors. The RH Y motor can be easily moved and the LH Y axis also moves but has a slight holding torque.

It's strange that its both Y axis motors and one slightly worse than the other.

switching the dip switches  for full current instead of half current made no difference.

[lloydsp]

Hmmm... it almost sounds like a motor problem.  I can't fully diagnose it from your reports.  But if you swapped one with an X driver, and it still had insufficient torque, it sounds like the motors.

OTOH... what is the pitch of your screws on the Y axis, vs. the others?  If you have a 'long' pitch on Y (fewer turns per unit of travel) than on X and Z, that might be the source of what you're seeing.

If the screws are of the same pitch in all three axes, then I would suspect the motors.

Lloyd

[martyncnc]

I don't believe it... it was the grub screws on the pinions on the stepper shafts. Both the Y axis grub screws had come loose... the RH was really loose and the LH was a bit loose.

I'm swapping those pinions for some with 2 larger grub screws

[lloydsp]

OH, YEAH!  That's the BEST outcome!  Someone else had suggested the screws, but I didn't pursue that angle.

I'm glad you got it solved.

Lloyd

[martyncnc]

Check the tightening of the couplers that connect the motor shaft with the screw. If they have become loose they may be slipping while the motor is actually not turning.

Credit due

[Dragonfly]

Credit due