The original direct drive Airtripper V3 extruder that I had made for my Rostock-Mini was almost able to get the job done. However, my stepper just didn’t quite have enough torque to push the filament directly, and it would “skip” steps relatively continuously. I could still print large objects, but they would have a “foamy” appearance due to using less plastic than they really should. Also, my stepper motor and drivers were getting hot due to all the extra current flowing through them.
I finally decided it just wasn’t going to work well enough for production use, and printed an extruder (Gregs Accessible Wade extruder) that has a printed gear system for a large mechanical advantage. I adapted it to feed into my Bowden tube and mount onto the top of my Rostock-mini frame with two printed parts.
It made all the difference in the world. My geared extruder can now easily feed filament continuously through the hot end at a 300mm/min rate.
I also printed an adapter plate that holds the stepper motor and attached extruder in the appropriate location/angle. In the future I may integrate this with parts from Gregs Wade extruder design to build an integrated extruder.