Z motors wont move together

nophead

Motors in series get the same current but half the voltage. That means the maximum speed is lower but at low speed you should get identical torque and with 3.4V motors on 24V you should have plenty of speed.

Are you sure one axis isn't binding mechanically? Can you turn each motor by hand and feel the same resistance?

If you are trying to move too fast then one motor will tend to stall and the other run when in series. Have you tried moving very slowly?

Xandrel

If I switch the port the motors plug in, the opposite motor will work. Its as if there is a drop in power from one motor to the next. So the first one works well, the next doesnt have enough power. Its not isolated to any particular motor, but the order in which the power cycles through them.

1 question. If the Duet can handle running at 80% of 2.8A, why does the configurator say the maximum is 2000ma. Am I missing something? Can I put a value of 2240ma? Cause thats what I did.

deckingman

@xandrel said in Z motors wont move together:
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1 question. If the Duet can handle running at 80% of 2.8A, why does the configurator say the maximum is 2000ma. Am I missing something? Can I put a value of 2240ma? Cause thats what I did.

The maximum motor current that the Duet boards used to be able to handle was 2.0 Amps but that specification has fairly recently been increased to 2.4 Amps. https://duet3d.dozuki.com/Wiki/Choosing_and_connecting_stepper_motors

I'd say that the configuration tool just hasn't been updated.

nophead

@xandrel said in Z motors wont move together:

So the first one works well, the next doesnt have enough power. Its not isolated to any particular motor, but the order in which the power cycles through them.

Sorry but that makes no sense electronically. I think you must have an error in the wiring to the motors. Are you sure each motor is wired to just one of the plugs and you haven't mixed them up somehow?

nophead

It is actually behaving like one of the sockets is shorted. The motor plugged into that one would not spin but the other would.

dc42

@nophead said in Z motors wont move together:

It is actually behaving like one of the sockets is shorted. The motor plugged into that one would not spin but the other would.

I agree. Check that there are no solder bridges between pins of the Z motor connectors on the underside of the Duet. I recall seeing a report of a board with this fault recently. It didn't get picked up during testing because the boards are tested with the 2 jumpers in the Zb position, just as they are shipped.

Xandrel

@nophead said in Z motors wont move together:

It is actually behaving like one of the sockets is shorted. The motor plugged into that one would not spin but the other would.

@dc42 said in Z motors wont move together:

I agree. Check that there are no solder bridges between pins of the Z motor connectors on the underside of the Duet. I recall seeing a report of a board with this fault recently. It didn't get picked up during testing because the boards are tested with the 2 jumpers in the Zb position, just as they are shipped.

I took a quick look at the board this morning, front to back, and cant see anything visual. I inspected the motor wires and connectors and cant see anything wrong. I trust the next step would be to check the pin headers with a meter for shorts?

Should I be running the motors off their own driver anyways at this point? There seem to be more benefits that way anyway?

jckray

I have been having a slightly different issue with my z motors, but perhaps it could be related so I'll post here too.

I have had many a successful print of the printer I built, however sometimes at the end of a print, or after a print has finished and upon starting up a new print, the z-axis motors decide to move out of sync. This seems very weird to me. As I understand it, this should not be possible since both motors are run from the same driver. I have had this issue across 3 different models of the printer shown in this video. All using the Duet Wifi, and two .4A steppers with integrated lead screws fro the z axis. The hardware and duet configuration is identical across all 3 printers. Power cycling the printer always resolves the issue.

Perhaps the motors are been driven too fast? I know the z motors are in series so this greatly reduces torque over a certain speed.

Another thought I had was maybe this has something to do with how RRF handles idle currents.

I also have a single motor with the same specs as the z motor running of another driver on the board, which is used for a multilateral system. I have had no issues with this motor at all.

[0_1541572296923_IMG_1315.MOV](Uploading 100%)

jckray

@jckray Video link

I realized I shared that video for my earlier post incorrectly. This link should work.

dc42

@xandrel said in Z motors wont move together:

Should I be running the motors off their own driver anyways at this point? There seem to be more benefits that way anyway?

As they are large motors (Nema 23), I would recommend that. But they should work in series if you don't ask for high Z speeds.

Xandrel

Just to confirm, I did finally get back to looking at this issue and have temporarily solved it. I made a splicer so that I could put both Z motors into the same socket on the Duet, and it worked. This leads me to believe that the problem is a hardware issue on the Duet itself? Would you agree?

elmoret

@xandrel Does your splice put the coils in series or parallel?

Xandrel

@elmoret It would be parallel.

dc42

I suspect you were trying to run them too fast for a series connection. Now that you have them connected in parallel, they will receive half the current each, so the torque provided by each motor will be halved.

Xandrel

@dc42 I would imagine for the z motors, speed and torque is not much of an issue as its only raising and lowering the printing gantry at a slow speed. The only fast movements it would do is during probing. Perhaps I am missing something? Either way, continuing with the project in this capacity is perfectly fine for me.