i3 MK3S+ Extruder axis (motor) not moving  

RE: i3 MK3S+ Extruder axis (motor) not moving

the stepper motor has 4 wires, if any one breaks, the motor just quivers, in place... 

maybe you have fatigue fractures in the wiring loom! 

regards Joan

RE: i3 MK3S+ Extruder axis (motor) not moving

Is there a way to test this theory?

Since there is no access to the wires on the motor's end I can't check continuity.

Thanks,

RE: i3 MK3S+ Extruder axis (motor) not moving

the motor has two coils  Black and green wires connect to one coil, and red and blue connect to the other, ~

remove the plug from the motherboard connector, and use a multimeter to test for continuity, 

Beware, if you move the print head, the broken wire may touch together  and look ok.
If this happens you will need to undo the wiring loom, and pull on each  wire, individually. this should identify which wire is faulty. 

regards  Joan

RE: i3 MK3S+ Extruder axis (motor) not moving

I've been struggling with this problem with a while now, and one of the difficulties is that it comes and goes. I thought I fixed it (though I don't know exactly what I did that would have fixed it) and had very good prints for a while, but but now the problem seems more severe. I tested the motor wires as you suggested and it's not them. Continuinity tested fine and no matter how much I jiggle the wires they are ok.

Prints are now failing quite consistently; some time during the print the Extruder motor stops moving.

I thought it was due to a clogged nozzle so I replaced it; that did not help.

I ran a print without filament and I saw that at the beginning the Extruder motor moves as expected, but somehwere along the print it stops moving even though the rest of the machine goes through the motions of the print.

If I try to unload the filament after the print gets stuck like that I can hear buzzing from the motor but it does not really move. If I reset the machine and then try to unload the filament the motor moves as expected and unloaded the filament.

What could cause the Extruder motor to stop moving during a print? Can it be a FW issue?

Thanks,

RE: i3 MK3S+ Extruder axis (motor) not moving

If the problem is intermittent, then it has to be a wire and you cannot check it while it is in the loom.  Over the decades, I find that a hard pull on a suspected wire is the only way to find an intermittent break.  Look at any location where the wire may bend the most.  Top of the Einsy housing or just at the beginning of the loom.  Or, if the motor wires were pulled tight into a sharp bend, then right at the motor. 

When using a meter, the amount of current going through the wires is very low.  A break may not show up with a meter but when you try to put current through the break to drive the motor, the resistance at the break will stop the motor from turning.  I have taught many techs, where current is involved, a test light is better than a meter for testing continuity.  I have seen an ohm check pass but a test light fail.  From a search, the motors are rated at 1A of current.  It wouldn't take much resistance to stop the motor from turning.  You can then add in some thermal effects into the mix.

RE: i3 MK3S+ Extruder axis (motor) not moving

I wish the problem was with the wires (wishing in the sense of finally knowning what the problem is), but it does not fit the data.
1. I played with the wires any way possible, no impact on the motor's behavior.
2. When I run a full print with the idler door open and with no filament I see the extruder motor spinning throughout the print. If the problem was intermittent I would expect the motor to stop turning during these prints as well.
3. When I close the idler door (still no filament), the extruder motor will get stuck at some random point (I checked the angle at which it gets stuck and it is different every time). Obviously it gets stuck with filament too.
4. About two weeks ago I decided to vacuum the inner chamber of the extruder motor axis and I found a piece of filament that got wedged there. It probably broke off during one of the filament unloads. I then had a very good run of prints without fails, but then the problem returned. I vacuumed again, didn't help. Tried a copmressed air canister to dislodge anything that might be stuck there, didn't help. I released the screw of the internal Bondtech gear so I could move it back and forth and rotate freely, but found nothing that could cause the problem.
I'm back to square one with the same problem, only now I cannot find a reason for it. 🙁

RE: i3 MK3S+ Extruder axis (motor) not moving

I am still thinking it is a wiring issue.  A partially broken wire will allow some current through but when the motor is under load, the motor won't have enough voltage at the motor to drive the motor.

Stepper drivers work with current regulation, not voltage.  That is why you can run stepper motors on different supply voltages.  A concept that some don't understand.  Controller will do what it can to ensure that the current is correct for the motor.  If the number of strands of wire are broken, then you could measure continuity with a meter and it looks good, yet, if you try to put any current through the system, then you have an issue.  One of the reason I use an incandescent test light for checking wiring to ensure that I draw current through the wires and them measure the voltage.

Since you say that the motor sticks in different locations, isn't a clear sign that it isn't the motor.  Stepping coils are the same and not part of an individual point on the motor. 

Closing the idler door will add load to the motor and will increase requried torque.  Higher resistance in the wire due to some broken strands will generate a voltage drop to the motor and not allow enough torque for the motor to drive the filament.   Motor is getting correct current with a lower voltage, less power.  Some information on how stepper motors work.

Impact of Voltage and Current on Stepper Motor Performance

If I had your issue, I would setup an Arduino with a stepper driver and test the motor that way.  Lock the motor in different points and measure the voltages across the wires.  Testing on the printer I would close the idler door, using some scrap filament, manually run the motor with the idler door adjusted tighter than normal.  I would use a pin to allow me to measure the voltage at the motor.  A pin is use to cut through the insulation with a small hole.  My meter came with probes that will put a small hole in the wire insulation to allow me to measure voltages. 

RE: i3 MK3S+ Extruder axis (motor) not moving

First, thank you very much for all the information.

What you suggest is still a possible reason, but the long run of good prints I had after removing the filament residue is not explained. It was like the printer came back to life and printed as if it were new. The prints do not show any signs that the motor was skipping, lagging, or anything like that.

RE: i3 MK3S+ Extruder axis (motor) not moving

I thought you were still having issues.  My mistake. 

A piece of filament can interfere with the movement of the feed mechanism.  You can use friction to enable/disable a gear mechanism as in the release clutch on an electric drill, as I found out on the weekend.  The piece of filament, depending on where it was, it may have been able to jamb up the filament drive.  Never seen it myself.  I have seen filament jamb and the drive gear grind the filament when I had a blocked nozzle.

RE: i3 MK3S+ Extruder axis (motor) not moving

I still am having issues, sorry if I confused you.

I meant the good run of prints I had before the problem returned. Many prints succeeded without issues, and this is strange to me if the problem was an intermittent issue with the motor. Now the problem is back and is extremely quick to manifest itself. Prints will fails on the very first layer or at most after about 10 layers.

The long run of good prints after the filament removal and the fact I get nowhere with playing with the wires is what I cannot reconcile with a wire motor issue.

Disconnect and dismount the motor.  Turn the shaft by hand.  Is it smooth?  You should feel the steps as gentle bumps but no grating and no stiffness...

Cheerio,

RE:

That is a very good idea. Is it possible to disconnect and dismount the motor without disassembling the entire array of the E-axis assembly?

RE: i3 MK3S+ Extruder axis (motor) not moving

I am looking at the assembly manual for the MK3S+ and the screws to mount the motor are inside the print head.  To manually rotate the motor, you will have to either use a tool through the access cover or disassemble the head.  Download the MK3S+ assembly manual.  Section 5, E-axis assembly.  Here is the link.

Original Prusa i3 MK3S+ kit assembly (v3.26)

Put a request on on the forum for a spare motor.  With people that have done upgrades over the year, there may be a few low cost replacements available.  With this issue, I would be tempted to change the motor if I was pulling the head apart.  You can order a replacement motor from Prusa.