Omerod 2 Extruder Motor changes

Hey everyone,

I am currently using an Omerod 2 printer and attempting to print with a temperature sensitive polymer. The problem is that I need more torque than the stepper motors that came with the printer provide. I have purchased a new stepper motor with a gear ratio of 50:1 -- this is the Nema 17 planetary geared stepper motor (specs attached). When I connect the motor to the duet board, I can hear it make noises but the driver does not rotate at all. To confirm that the motor even works, I hooked it up to a raspberry pi and it rotated just fine. So my questions are

How could I overcome this lack of rotation from the duet board? I suspect there is not enough voltage getting to the motor -- is there anyway to step this voltage up?

And secondly, Since I know that a pi can run all of these motors, is there a way to get the pi and the duet board to communicate?

Thanks!

-Luke

in my experience with steppers, makes noise but doesn't rotate is often a case of miswired connections.

afaik, for voltage, the steppers are provided the input DC voltage that you feed the duet (12vdc nominal for most people). You can increase the setting for stepper driver current via the config g-code. M906 I think?

A ration of 50:1 is far too high because the motor will need to rotate at an insanely high speed and the rotor inertia will prevent the motor from moving unless you set the acceleration very low. Even 5:1 gearing on top of the approx. 3:1 gearing in the extruder is probably too much.

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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].

@dc42

Thanks for your reply! I'm trying to understand what you mean exactly (forgive me as I am relatively new to this printer)
So are you saying that based on the board that I have, any gear ratio that is higher than 5:1 wouldn't work even if given enough current through the board? And this is due to the speed that a 50:1 gear ratio motor would optimally rotate at?

@Achaz

I have tried every wiring configuration possible and it is still not budging at all. Thanks for the advice on that currents command, though! That will be useful in the future (and you were right about the Gcode numbers )

The higher the gearing you use, the more torque you get from the final shaft, but the higher the motor speed you need for a given final shaft speed. There are three problems with high motor speeds. One is that the higher the motor speed, the higher the drive voltage you need to the stepper driver, to overcome the motor inductance and back emf. The second is that the motor acceleration is ultimately limited by rotor inertia, so the higher the gearing, the lower the acceleration you can get on the final shaft. The third is that you may ultimately reach the limit at which the firmware can generate stepper motor pulses.

If you reduce the extruder acceleration, speed and jerk settings by a factor of 50 and increase the steps/mm by a factor of 50 compared to the normal settings, then you should be able to at least make the motor move if you have wired it correctly.

The 3:1 gearing on the Ormerod extruder is close to optimal IMO. Few filaments need more extrusion force than PLA. If you do need a higher extrusion force, I suggest you substitute an ungeared motor with higher torque.

HTH David

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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].

If the Pi turns the motor, so will the Duet. If the Duet is not turning the motor, it will be because of a wrong configuration or hardware fault. Remember that the Duet will not turn the extruder if the hotend is cold unless you first enable cold extrusions. I am not quite understanding your issue - you mention using a special type of plastic. Does your printer work OK with more common types of filament but fails only with that type?

Dave

So the problem is purely based on the motor. I am not extruding a plastic through the hot end -- I have completely taken the given extruder off and have 3d printed my own set up. This new set up relies on the torque that the original extruder motor supplied in order to extrude the polymer I am using from the set up that I made. The polymer requires higher torque in order for it to properly print than the original extruder motor affords. So I am only trying to switch out the motor to drive this new set up -- not switch the motor that feeds the given extruder.

where would I be able to mess around with the acceleration, speed, and jerk settings of the printer? And thank you for the idea of maybe using a different motor, I will look into that as well.

-Luke

If you are using the extruder for a different function to usual, are you sure that the Duet is trying to drive the motor? As said, if it is not receiving a hotend temperature input indicating a temperature of above 170 deg or so, it will inhibit the extruder drive.

You can set acceleration with the M201 command [reprap.org] However the extruder acceleration would not normally be the limiting factor (there is no inertia in the extruder system), acceleration would usually only be set for X & Y.

Extrusion speed is not set independently, it is determined by the volume and speed of each print move. To slow the extrusion speed, you can print slower, set a smaller layer height or set a thinner extrusion width.

Dave