Extremely Low Torque to Extruder Stepper Motor

Triffid_Hunter Wrote:
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> casainho, I just ordered some A4983 carriers from
> pololu, instead of reprap stepper boards. my
> steppers are also 2.77v, 0.44Nm ones so current
> chopping is critical, and the 16x microstepping
> may not be much help for the axes but will be
> excellent for the extruder.

Thanks ;-) I already bought things from Pololu in the past and they were nice.

So, I can buy one A4983 board from Pololu for $13 (by the way, they have very good documentation for it!!!!)

Where can I buy the 2.77V, 0.44Nm stepper motor?

Although I bought a DC motor with 3x more torque than the one I currently have, I would prefer to use a stepper motor... and that one of 0.44Nm have the double torque of mine :-)

I got mine from [ausxmods.com.au] but I suspect you'll prefer a local supplier

[objects.reprap.org]

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[www.hydraraptor.blogspot.com]

I bough the stepper motor controller from Pololu: [www.pololu.com]

And I also bought the NEMA 17, part number SY42STH47-1684B from Zapp Automation.

Thanks ;-)

Just a heads up, Adrian just changed the firmware in svn to use the pot. This works out of the box for me. All I need now is a gear that'll fit inside the extruder, and get enough grip

From Adrian:

M110 ;makes the machine listen to the pot.

M108 S0.5 ;Makes it ignore the pot and sets the PWM to 50%

I've also amended the Java host software, but I haven't checked that back in as I'm developing other parts and there are still bugs. Here's the code (from GCodeRepRap.java) if you want to do a patch:

public void selectExtruder(int materialIndex)
{
int oldPhysicalExtruder = getExtruder().getPhysicalExtruderNumber();
super.selectExtruder(materialIndex);
int newPhysicalExtruder = getExtruder().getPhysicalExtruderNumber();
if(newPhysicalExtruder != oldPhysicalExtruder || forceSelection)
{
gcode.queue("T" + newPhysicalExtruder + "; select new extruder");
double pwm = getExtruder().getPWM();
if(pwm >= 0)
gcode.queue("M108 S" + pwm + "; set extruder PWM");
else // <- New
gcode.queue("M110; set extruder to use pot for PWM"); // <- bit
forceSelection = false;

fynflood Wrote:
-------------------------------------------------------
> Just a heads up, Adrian just changed the firmware
> in svn to use the pot. This works out of the box
> for me. All I need now is a gear that'll fit
> inside the extruder, and get enough grip
>


That is fantastic - I will have to try it out ASAP!

Does anyone have the solution to this problem because I have exactly the same problem, Gen 3 electronics and stepper motors from MakerBot. On the X, Y and Z-axis it is impossible to move the stepper motors when they are energized (I'm not sure even vice grips would be enough to do the job). But, the exact same stepper motor connected to the extruder controller can be easily turned with two fingers.

I will never be able to extrude the way it is right now.
It must be a setting on the extruder!

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Bob Morrison
Wörth am Rhein, Germany
"Luke, use the source!"
BLOG - PHOTOS - Thingiverse

The Makerbot motors I have are 14V so they would not need any PWM and they don't have a lot of torque for an extruder. The recommended motors for Mendel are low voltage so would need a small mark space ratio on the PWM to avoid overloading the driver chips, so perhaps that is the default setting.

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[www.hydraraptor.blogspot.com]

I have tried both 50 and 700 (140 is the default) in the code.
Adjusting the pot also does nothing.

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Bob Morrison
Wörth am Rhein, Germany
"Luke, use the source!"
BLOG - PHOTOS - Thingiverse

My guess would be the max is 255. I think you set it to zero with the M code to make the pot control it.

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[www.hydraraptor.blogspot.com]

@nophead: I just don't think it is the stepper motor since when attached to the stepper controller board it is impossible to budge the motor when energized, BUT when attached to the extruder controller it requires no effort at all to move the motor. It barely resists at all - THIS IS THE PROBLEM! Ergo, the stepper controller must be using less voltage (or current) to drive the stepper motor. The only thing I can think of is to look at the signal to the stepper motor from the stepper controller and compare it with that coming from the extruder controller. If it acted the same and wasn't strong enough then I would say that the stepper motor doesn't have enough torque, but since they react totally differently I don't think so...

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Bob Morrison
Wörth am Rhein, Germany
"Luke, use the source!"
BLOG - PHOTOS - Thingiverse

Changed pwm values on the extruder controller will only take effect after the next step of the motor. So turning the pot won't make the motor immediatly "stronger", it has to turn to see an effect. Perhaps that's the problem.

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[yetanothermendel.blogspot.com]

No you have two problems I think. The extruder controller is expecting to drive a low voltage motor so it defaults to a low PWM ratio, otherwise it would fry when using the recommended motors. You should be able to set the PWM to 100% and get the same torque as the other motors, i.e. full 12V drive.

The recommended motor for the extruder is a high torque NEMA17. The Makerbot ones are not very high torque, especially when run from 12V because they are 14V motors. You might get enough torque with Adrian's geared design, but I think it will struggle on any of the other designs. The table at the end of this article compares the motors: [hydraraptor.blogspot.com]

At 12V the Makerbot ones will only about half the torque of the FL42STH47-1684A-01.

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[www.hydraraptor.blogspot.com]