The second motor of my BitsFromBytes laser-cut extruder, a GM3, has just failed. I do have not a record of the time it has been operating but I estimate it is between 5 and 10 hours, running with M108 S120. The gearbox looks OK but the brushes of the motor are worn. Is this a reasonable life for the GM3 motor/gearbox? Any suggestions for a more robust replacement without building a different extruder? https://reprap.org/forum/read.php?14,22670,22670#msg-22670 Fri, 09 Oct 2026 01:07:01 -0400 Phorum 5.2.23 https://reprap.org/forum/read.php?14,22670,23442#msg-23442 https://reprap.org/forum/read.php?14,22670,23442#msg-23442 This means if we use PWM alone, the speed varies.

Adding an encoder allows the controller to run the motor (and therefore the filament) at a constant speed.

Stepper motors have also been used to drive the extruder - they have more control of the rate, and more torque.]]> DaveR Mechanics Sun, 10 May 2009 05:53:42 -0400 https://reprap.org/forum/read.php?14,22670,23439#msg-23439 https://reprap.org/forum/read.php?14,22670,23439#msg-23439 I am new here, so I am not too familiar with specifics of the Reprap and its motors, but I do know a lot about motors in general (steppers and DC motors).
I don't understand that you say "It naturally runs much faster and, slowing it down to an appropriate speed, the torque is too low."

Torque delivered by a dc motor is linear to the current that you drive it with. If you experience the torque is too low at low speeds, you are not pushing enough current through the motor. This can have several causes.
My guess after reading your situation is the following: you drive the motor with a PWM signal. You regulate the speed of the motor with the PWM signal in a no-load situation. When the mechanical load of the system increases, the motor stops. The current is simply too low because the net voltage on the motor (%PWM*driver voltage) is low.

To get a constant speed you need a speed controller. And for that you need some kind of feedback. Widely used in the industry are incremental encoders.]]> TomNagel Mechanics Sun, 10 May 2009 04:27:01 -0400 https://reprap.org/forum/read.php?14,22670,23423#msg-23423 https://reprap.org/forum/read.php?14,22670,23423#msg-23423 DaveR Mechanics Fri, 08 May 2009 13:23:05 -0400 https://reprap.org/forum/read.php?14,22670,23420#msg-23420 https://reprap.org/forum/read.php?14,22670,23420#msg-23420 jonwise Mechanics Fri, 08 May 2009 10:51:20 -0400 https://reprap.org/forum/read.php?14,22670,23251#msg-23251 https://reprap.org/forum/read.php?14,22670,23251#msg-23251
I think the motor for the solarbotics GM3 is the same size as those used in 1/32 scale slot cars (they agree to a couple thou when I measure them, and the shaft diameter is dead on.) Slot cars use 12 Volts (in the U.S. I don't even know if slot cars are much of interest elsewhere....)
I suspect that the torque/Amp is as good as the GM3 motor, but I haven't checked that. So, 1/32 scale slot-car motors seem like an option.

Possible improvement?
Slot car motors are often available with dual shafts. If one were to replace the GM3 motor with a dual shaft motor, one could put an encoder off the back shaft.
Given the gear ratio involved, one could measure velocity much easier from the motor shaft, and could do so with a very simple (read coarse) encoder disk -- half white and half dark. (Or four alternating light/dark quarters if you want to gild the lilly.)

I bought some dual-shaft motors for this purpose, but haven't tried them out yet.
(I have some distractions of late. We just {today} started a major remodeling project on our house.)

I got dual-shaft motors from www.brshobbies.com The exact part I bought is no longer stocked, but I emailed and got the equivalents. (And I got a reply within the hour.) Looks like his AUTOart #13300 Motor (or 13302) are both dual shaft. They're USD $5.95 +shipping.

-------

Larry,

We no longer carry the SCW1 motor but stock some AutoArt dual shaft motors. Here is the link: [www.brshobbies.com]

Best regards,
Brian
BRS Hobbies]]> Larry_Pfeffer Mechanics Thu, 30 Apr 2009 18:27:46 -0400 https://reprap.org/forum/read.php?14,22670,23239#msg-23239 https://reprap.org/forum/read.php?14,22670,23239#msg-23239
To correct my original post, the second motor had not burnt out. It stalled with similar symptoms to the failed first motor but further investigation showed the problem was elsewhere. The HDPE had developed a kink between the extruder drive screw and the channel down to the heater barrel. It has happened twice more and this problem is perhaps a topic for a different thread.]]> jonwise Mechanics Thu, 30 Apr 2009 12:57:31 -0400 https://reprap.org/forum/read.php?14,22670,22732#msg-22732 https://reprap.org/forum/read.php?14,22670,22732#msg-22732 Forrest Higgs Mechanics Wed, 08 Apr 2009 15:50:38 -0400 https://reprap.org/forum/read.php?14,22670,22724#msg-22724 https://reprap.org/forum/read.php?14,22670,22724#msg-22724 nophead Mechanics Wed, 08 Apr 2009 10:27:43 -0400 https://reprap.org/forum/read.php?14,22670,22723#msg-22723 https://reprap.org/forum/read.php?14,22670,22723#msg-22723 -------------------------------------------------------
> I am not sure. It looks the same but I didn't
> notice the 12V GM3 going any faster than the 6V
> GM3 run from 12V. You could ask Solarbotics, they
> seem pretty helpful.

It does go faster. I measured once and determined that it is about half again faster at 12v as the 6v motor is at 6v.]]> Forrest Higgs Mechanics Wed, 08 Apr 2009 10:19:47 -0400 https://reprap.org/forum/read.php?14,22670,22721#msg-22721 https://reprap.org/forum/read.php?14,22670,22721#msg-22721 nophead Mechanics Wed, 08 Apr 2009 08:04:48 -0400 https://reprap.org/forum/read.php?14,22670,22720#msg-22720 https://reprap.org/forum/read.php?14,22670,22720#msg-22720 jonwise Mechanics Wed, 08 Apr 2009 07:41:27 -0400 https://reprap.org/forum/read.php?14,22670,22715#msg-22715 https://reprap.org/forum/read.php?14,22670,22715#msg-22715
I think they do sell the motors separately though and it is easy to just swap the motor.]]> nophead Mechanics Wed, 08 Apr 2009 04:06:25 -0400 https://reprap.org/forum/read.php?14,22670,22714#msg-22714 https://reprap.org/forum/read.php?14,22670,22714#msg-22714 jonwise Mechanics Wed, 08 Apr 2009 04:02:49 -0400 https://reprap.org/forum/read.php?14,22670,22672#msg-22672 https://reprap.org/forum/read.php?14,22670,22672#msg-22672
My experience with GM3 is that the 6V motors (white end cap) have very thin brushes and last for tens of hours. The 12V motor (black end cap) has better brushes and lasts 100's of hours.]]> nophead Mechanics Mon, 06 Apr 2009 15:29:42 -0400 https://reprap.org/forum/read.php?14,22670,22670#msg-22670 https://reprap.org/forum/read.php?14,22670,22670#msg-22670 jonwise Mechanics Mon, 06 Apr 2009 15:10:19 -0400