This project has reached its logical conclusion with all further development now continuing on the Arcus-3D-M2. Being born as a junkstrap, it inherently had a large number of variables to try to account for which was slowing development. Now that a clear goal has emerged, it was decided to eliminate most of these variables with a stronger, lighter, more standardized design. So go check out the Arcus-3D-M2.
The current design is based on a Beaglebone Black running a Machinekit velocity extrusion branch, and some custom code. The interface is published as a network service and can be accessed locally or remotely with an Android, Windows, or Linux client.
Five stepper motors located on a floating carriage push 1.75mm filaments down short, nylon bowden tubes to a compact, liquid cooled cold-end.
The all metal hot-end employs a tiny impeller located right at the melt-zone of the 5 distinct incoming plastic streams. The impeller spins at a relatively high speed and is designed such that it also generates it's own extrusion pressure to feed the nozzle. This greatly reduces the feed pressure required, eliminates feeding back into idle ports, dramatically improves color change performance, and helps to mitigate 'oozing'.
The impeller drive is a PWM controlled BLDC motor, and it is proportionally tied to the current extrusion rate.
Result: The ability to pick any ratio of the loaded filaments with a few M codes and complete color changes in 20mm of 0.4mm extrusion.
The remaining junkstrap bits I've retained:
- Parallel port based 4 axis board and 3 huge NEMA 34 steppers from a failed CNC project.
- Linear guides made from leftover aluminum extrusion from our Florida room, some screen door rollers, and pre-loaded with roller-blade bearings.
- Thermistor from a garage sale grill thermometer.
- Magnetic bearings from Harbor Freight ball bearings and Home Depot magnets.
- Bowden tubes made from the nylon feed liner from my old mig welder.
- Top and bottom built from oak plywood.