Why try using a DC motor as an extruder? It goes back to the recent (ish) discussions on print artifacts that are potentially caused by extruders.
https://forum.duet3d.com/topic/23502/vertical-lines-vs-geared-extruders/89
https://www.bondtech.se/2023/01/26/how-we-improved-our-plastic-main-gear/
https://www.bondtech.se/2023/03/09/turning-lemons-into-lemonade-chapter-two/
https://www.youtube.com/watch?v=c6JmCdovE0U
https://www.youtube.com/watch?v=UWuSsYKI-YM

I've always been fairly happy with the print quality I get out of my two BMG extruders, however I've been impressed with the surface quality of prints done by my Stratasys Dimension BST 1200es (excluding 'ringing' artifacts on direction changes). Inspired by the DuePrint project posted here and on Hackaday, I pulled the extruder off the Stratasys printhead, and worked to get it integrated onto my DIY IDEX machine.

Prior to that though - about a year ago I started looking into designing my own extruder - inspired by all innovations of the LGX, Orbiter, Sherpa, etc. I was using these extremely slim Nema17 motors (PKP242D23A2) that are similar in stature to the popular pancake motors used on the newer generation of extruders (chief difference being the larger shaft diameter). As I played around with designs, it felt like I was reinventing the wheel - why not use a small stepper with an integrated gearbox (aside from price... right?). Starting looking at 15:1 Nema11 motors from Oriental Motor (PKP223D15A-CS15), but then the extruder project fell to the wayside. This past October I came across a nifty Nema8 with a 16:1 gearbox, and have been using that in a few different extruder combinations.

Based on the DuePrint project, I figured integrating the DC motor into the existing design would be easy enough - and after working past some Beta2 bugs, it was!

58f07574-fdf6-42f6-abbc-378ab6955402-image.png
https://www.youtube.com/watch?v=vvajxcZIf6M

Unfortunately, my lack of knowledge starts to creep in. With the Geckodrive G320x, I'm getting excessive motor thermal rise (at extreme conditions, the controller/encoder has either faulted out, or I disengaged the motor based on concerns of it failing) within 15 minutes or so. I'm seeing at least a 35°C thermal rise, and if my chamber sits at 62°C, that is not good. The twist is (detailed temperature measurements pending) that the Dimension series chamber temperatures settle at 75°C, and the motors operate comfortably at that temperature.

The Maxon P/N on the motor and gearhead don't lead anywhere (nor have I directly asked them, assume its 'proprietary' to Stratasys), but I'm pretty sure they're the similar to the following:

RE 25 Motor - P/N 118743, 12V nominal voltage, 2.18ohm terminal resistance, 1.25A nominal current GP 32 Planetary Gearhead - P/N 166167, 86:1 (with the 8mm shaft option) 1000 CPT MR Encoder - P/N 225780

At slow speeds, I have to turn the current pot on the G320x to ~2.5A, and in normal printing conditions, I have to bring it closer to 4A. If I've identified a similar motor, that is much too high!

From the uPrint (very similar print head to the 1200es) service manual:

The 5 VDC and 12 VDC are used by the controller board, single board computer, and hard drive. The 12 VDC also powers the filament motors. • The 24 VDC powers the stepper motors, solenoids, fans, and chamber lights. • The 120 VDC circuit powers the model heater and a separate 120 VDC supply powers the support heater.

Block diagram of the uPrint/1200es - of note is the L298P Dual Full Bridge for the extruder motor.
2ac09183-a753-4fbb-b5ce-4b00635388f7-image.png

This means then for the DuePrint implementation... we're using the G320x to signal to the PDB, and in turn the L298P?
78917a25-2a7d-4236-8561-0dbdba83371b-image.png

Still doing some learning and digging around.

EDIT - Next Day Update:
Trying to use my brain here - my motor current estimates were based on how far I turned the current trimpot on the G320x (starting from 'off'). As one could expect, there is a bit of slop in the trimpot. For the setup with my DIY printer - Making the assumption that V.controller_in * I.controller_in = U.motor * I.motor, I finally hooked a meter in line with the motor controller input (24v supply). Testing at standstill (dithering) and slow 5mm/s feedrates, I'm sitting at roughly 24v * .4A = 9.6W. This took minuscule adjustments to the trimpot, closely monitoring the meter reading. I'm at a steady thermal condition, with ambient (chamber/bed is off) at 22°C, and the motor casement at 57°C (35°C rise, but may be wise to imagine the true range is 30°C - 40°C to include some error with the readings). Separate thermal testing inside the Stratasys is ongoing now.