Here is a simple mounting rig for the Duet 3 6HC main board and a Raspberry Pi 3B or 4B SBC for testing printer builds or to assist with RRF3 firmware / application development.
The fan mount will fit any 40x40x10mm blower fan. Most fans should be a friction fit, but if yours is loose, then insert a zip tie through the hole below the fan then wrap it around the fan's frame to affix it to the test rig.
A fan is optional, but recommended in addition to fitting heat sinks to the stepper drivers for proper cooling.
Use any filament, PLA is great.
Rough / fast print settings are acceptable, although for optimal fit a 0.4mm nozzle is recommended.
STEP files are included in the download for easy remixing.
The author hasn't provided the model origin yet.