Z-axis intermittently travels only one direction

Hi Reprappers,
I have been experiencing an unusual intermittent problem with my Ormerod (1, green from RS). The issue is that sometimes the Z drive will only move in one direction (downwards). For example, after a complete clean start with power off etc, I can connect with the web interface fine and use all the controls but sometimes when I hit the +1 Z, it moves downwards instead of up. Even after manually send the zero command for the Z axis, each subsequent command moves the head downwards. After hitting the reset button on the duet or cycling the power, I can usually get back to a point where initially, the Z drive works in both directions. At this stage I usually home the X and Y (which works fine) and then attempt to manually home the Z using the web interface controls. At this point, either everything works ok or the problem arises whereby all move commands go in the same direction. The issue does not appear all the time, some days when it starts, everything works 100% and I have about a dozen successful prints so I don't think there is anything fundamentally wrong. I upgraded the firmware to the latest 0.78c today along with the SD card files and having the same issue. I checked for loose connections on the board but everything seems ok. I'm pretty confident with electronics and mechanics but not sure what is the best way to troubleshoot this issue so any ideas or advice appreciated.

I suspect you have a dodgy connection at one end of the Z motor loom. But check that the threaded rod can be rotated by hand fairly easily when the stepper motors are off, and lubricate the thread rod with light machine oil if you haven't already.

---

Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

It's probably best to test the motor with no load on it (disconnect the Z axis leadscrew, and support the X axis with something under it), as it could just be the axis sticking. See: [reprappro.com]
And specifically for the Z axis, see the last three bullet points here: [reprappro.com]

If it seems to be that the motor is not moving correctly, here's our usual motor movement troubleshooting advice:

NOTE: If you are connecting/disconnecting motors from the Duet, make sure the motors have NO POWER. Disconnecting a motor with the power on may destroy the stepper driver on the Duet.

If there is a particular motor moving randomly, vibrating, or not moving at all, there are three areas to check:
1. The motor. These are generally very reliable - we have sent out over 10,000 of them, and had about 10 faulty ones.
2. The wiring. This is also generally very reliable, but it's possible it has been put together incorrectly, or there is a break in the wiring.
3. The electronics. The Duet may have suffered damage to the stepper driver.

To test, turn off the power to the printer, and swap the wiring at the Duet between two axes, eg X and Y, or Z and extruder. Make VERY sure you have connected the wiring correctly; check the wiring diagram. Turn on power, connect, and test BOTH axes. If the problem stays with the same motor as before, the issue is with the motor or wiring; if it swaps to the other motor, the problem is with the Duet.

If the problem follows the motor, turn off the printer, and replace the motor wiring on the correct pins. Then:

1. Check the motor wiring loom. We have had a few cases (in nearly 2000 kits!) where the motor loom is incorrectly wired. Compare the wiring loom, at both ends, with another, known-working motor loom; check that the colour order is the same, check that the wires are connected to the right pins of the plug into the motor. The crimps are quite easy to release from the housing, and put in the correct order.

2. It is possible there is a problem with motor, but this is rare. Connect the motor to a known-working wiring loom, and test it. Also, with the motor removed from the printer, rotate the motor shaft in your fingers. Does it feel notchy? We'll replace any motor that is faulty, under warranty.

If the problem appears to be with the Duet, most likely the stepper driver has failed. The main reason for this is a poor connection, or disconnecting the motor wiring when the motor has power going to it; for the technical explanation, see: [reprap.org]
If the axis has never worked, we'll replace the board under warranty.

Ian
RepRapPro tech support

Hi guys,
Thanks for all the info (and you guys are fast), I checked all of the items you mentioned above and it looks like the Duet has a bad Z driver. As soon as I swapped the loom between the Z and Y axis, the problem moved to the Y stage only being driven in one direction. I also noticed when I swapped them back that even though the Z was being physically driven in the wrong direction, it was reporting to the web interface that it had moved correctly. Since this has been occurring intermittently from the start would it be covered under the warranty? Or should I use this as an excuse to get a new board with the duex4 and look at multihead printing

Hi Dan_P

Email me on support@reprappro.com and we'll replace the board under warranty. If you could give a brief description, and link the thread here, that would be good. Also, if you bought through RS, we don't have access to the RS customer database, so please send me your full name, address, and some proof of purchase (copy of invoice), and we'll get the process rolling.

Ian
RepRapPro tech support