DC gearmotor with encoder for extruder drive

[snowygrouch 1]

Hi everyone,

It seems that although DC gearmotors were tried in early REPRAPs people struggled a bit with the

control and so moved on to using steppers.

Example being:

http://blog.reprap.org/2009/01/pinch-wh ... e-v11.html

Unfortunatley the steppers might be a bit easier to drive precisely, but some intial comparisons show

they are also about double the weight (ish) for a given output.

Does anyone have any sucessful experiences with DC gearmotors for the extruder ?

Thanks !

C.

[tomnagel 126]

I'm always in for improvements, but why would a DC extruder drive be an improvement?

You mention weight, but since the extruder is mounted on the frame, what drawback do you see for 500g extra?

On top of that, an accurate DC drive with encoder feedback requires quite some processor resources (high controller loop freqency (500Hz?)).

Therefore, I think the choice for steppers is a good one.

[snowygrouch 1]

A high performance DC motor is alot smaller and lighter than a stepper of equivalent

shaft power output. The reason this is interesting for me, is that I am considering

putting the motors on the printhead.

C.

[IRobertI 521]

Couldn't you just go with a smaller stepper with a larger gear ratio to make up for the lack of torque? Seems it would be much easier to implement.

[snowygrouch 1]

Yes I am looking at some very small steppers with a gear reduction of about 50:1

I have some some calculations on the extrusion forces, and also some tests.

However if you used a miniature DC gearmotor its possible to have even better power density.

But if its a massive pain to do, I might just stick with trying the 50:1 stepper motor reduction.

It seems like the electronics are all set up for steppers, so I might be stuck with that.

C.

[rude456 0]

 

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