To complete the extruder, I needed a stepper motor to drive the Moineau impeller through the Schmidt coupling. Wishing to keep the package as light as possible, I wanted to use a NEMA 14 stepper. Since the pump turns fairly slowly but requires a moderate amount of force, some gearing was required. I turned to an earlier project I did and posted to Thingiverse: Hypocycloid Gear Reduction.

The hypocycloidal gear reduction can be used with little modification with the Moineau pump. The upper case needs to have a flange added to mount the Schmidt coupling cover and the Schmidt coupling disk nearest the gear box needs to have a nut pocket put into it for an M5 nut. The Hypocycloidal gear reduction can be easily configured to give several ratios from 30:1 down to 4:1 in the same size package. This is explained in the second part posted on Thingiverse. By changing any or all of the impeller, the lower case, and the output, the final drive ratio can be adjusted. I feel this is a big plus given that I'm not sure what the final torque requirements will be.

Now we're at a critical stage: Time to pump something stiff through the extruder and see what happens! Stand by for Peanut Butter!