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Have I a faulty stepper motor?

Posted by picnic 
Have I a faulty stepper motor?
January 26, 2014 04:23PM
I've been unable to print the Orthogonal Axis Compensation Test Pieces because my Y axis loses its position. Now I know what you're all going to say, the Y Belt is slipping, but I don't believe this to be the case. When the print goes wrong the Y stepper makes noises as if it's hit the end of movement and can't move any where. When this happens the motor does not rotate.

I found that rapid movements of the bed back and forth would result in a lock up, 90% of the time going away from the Y limit switch (increasing Y). The lock up would be tight enough I can move the whole printer across the table. Initially I thought it must be something mechanical with the Y movement but if I remove the belt from the Y stepper and twist the stepper motor's spindle back and forth it will lock up. Is this a faulty motor? Do stepper motors lock up if you twist the shaft? I have some old steppers out of disc drives and connect get them to behave is the same way.
Re: Have I a faulty stepper motor?
January 26, 2014 05:19PM
picnic, once powered up, the motors fight to stay still (holding torque) unless told to step, so not necessarily a problem motor, unless it behaves the same way when 12V is off. The same goes for moving the stage manually in the Y direction - powered up it will be hard, powered down it should move gracefully.

Other things to check are, is the belt looped correctly? Is the belt trapped anywhere? do the teeth catch on a slot ? is the idler bearing rotating freely? with the stage removed, do the bearings slide freely?

Re: Have I a faulty stepper motor?
January 26, 2014 06:22PM
Hi picnic

We've had a couple of motors returned (out of about 3000!) that have had problems. One of them was similar to yours, in that it would move properly, then stick. You can test this by removing the motor, and turning the motor shaft. Does it periodically lock? I took apart the motor that did this (remove the 3 or 4 screws, pull faceplates off, pull out motor shaft, note order of bearings, washers and thrust washer), and blew over it with air. I couldn't see any problem, put it back together, and now it doesn't lock.

It is possible to get contamination into the motor, like small bits of swarf or solder from when the connectors are soldered. Maybe it fell out when I took it apart. If you want to give it a go, before emailing me for a replacement ( support at reprappro dot com ), feel free!

RepRapPro tech support
Re: Have I a faulty stepper motor?
January 27, 2014 04:33AM
Thanks Ian, I'll try and blow any contaminates out before requesting an RMA. The spindle tests I did were with the motor disconnected from the electronics and the Y belt, so effectively free, and it was still sticking.
Re: Have I a faulty stepper motor?
January 27, 2014 05:24AM
Depending how regularly it happens, it might be worth checking it's definately a motor problem and not a problem with the board. I had what appeared to be an extruder motor that never worked (juddered, but wouldn't rotate); but after troubleshooting with another motor/loom, i narrowed it down to the board, which RRP kindly replaced. As yours is intermittent, it may well not be that, but still worth checking.
Re: Have I a faulty stepper motor?
January 27, 2014 01:45PM
All four of my motors had some degree of degradation on the terminal pins. One (kindly replaced by Ian) had a pin totally missing - melted down to a perfect little blob actually. I can only assume the motor inspection/test involved pulling a live connector off with plenty of volts trying to keep the circuit closed. Anyway, another one of the other motors had lost the plating on the same pin and was losing steps - the winding resistance is low enough that any additional resistance is unwelcome, especially with only 12V available for headroom. I suggest you take a good close look at the pins in the motor connector shell.

Edit: added photo of melted motor pin as supplied:

Some metal vapor can be seen deposited on the plastic shell above the pin, and I think this stuff was contaminating some of the pins on the other motors.

Edited 1 time(s). Last edit at 01/27/2014 03:45PM by Radian.

RS Components Reprap Ormerod No. 481
Re: Have I a faulty stepper motor?
February 03, 2014 08:55AM
Just wanted to say thank you to Ian and Reprap support for shipping me out a replacement stepper motor. I've now managed to print the calibration piece so onwards and upwards smiling smiley

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