SummaryI designed a direct drive extruder setup that is similar to the Printrbot. It uses the lever arm style filament pusher. All you need to print are the four parts:

Extruder Base Arm v5 Arm Pin Arm Spacer

The holes for the extruder base are spaced out exactly for a nema 17 stepper motor. All you need to do is drill out the holes once printed and just use longer hardware to secure everything together. I am using M3 nuts and bolts to screw everything down. I found that a golf tee works great for the pin that runs through the ball bearing. Ball Bearing Dimensions: 10mm OD 5mm ID 4mm Thickness As for the spring, I just used some bed springs and sandwiched it in between a M3 nut, washer, and M3 bolt. Print SettingsPrinter Brand: RepRapPrinter: Prusa I3Rafts: NoSupports: NoResolution: 0.1Infill: 40