The Orbiter" 140g direct dual drive Extruder with 10 kg pushing force

Last crawled date: 3 years, 5 months ago

Hi everyone! This is my latest design, a high precision direct extruder using a planetary gearbox plus the big (12mm diameter) dual drive bondtech style gear-set.

Short spek:

Gear ratio - 7.5 and 7.2
Filament pushing force 120Ncm (max theoretical) - 12.4 Kg (Wantai stepper)
Filament pushing force 103Ncm (max. theoretical) - 10.5 Kg (LDO stepper)
Filament acceleration up to 660mm/s^2
Retraction speed: 60mm/s
Overall weight is about 140g
The extruder is driven by a small round nema 14 stepper.

The orbiter printing @ 200mm/s on my MachCube 2.1:
https://youtu.be/aZolOWtBbME

In the last months I have experimented with worm gear based extruders with very good results, however not perfect so I decided to go for a different approach.
What I have learned is that the worm gears are not the best choice for extruders. Although high gear ratio gives a good theoretical filament pushing force in reality this is not always true, mainly because the worm gear efficiency is pretty low.
The plastic printed gears are even worse, at high torque their efficiency is well below 50%. The plastic worm gears tooth's are bending a little causing pressure variation in the nozzle which leads to some tiny wavy artifacts on the printed surface.
20-30:1 gear ratio reduces a lot this effect but the stepper will not be able to provide decent filament acceleration slowing your printed drastically down because it has to wait for the extrusion (this is the case for the Zesty Nimble, the flex3drive drive with Nema8 and my previous worm gear based extruders as well, acceleration below 100mm/s^2).

Because of the above arguments I decided to go with a different approach, using a planetary gearbox (efficiency over 96%). In the same time I have changed from the small dual hubs (5mm) to the bigger ones (8mm) because the depth to which the hub tooth bites in the filament is more constant over different materials. More teeths comes in touch with the filament. There is a slightly better grip on the filament resulting a more accurate extrusion. On the downside the bigger hubs ad more weight.