A limitation of current (affordable) 3D printers is their use of
open loop controllers and
stepper motors which limits reliability (drove the motor too quickly and skipped a step? Your model is ruined) and precision (~300 steps per revolution). A new project,
Servo Stock instead uses cheap RC
Servomotors combined with Hall Effect sensors, using a
closed-loop controller to precisely position the extruder. The Servo Stock is derived from the
delta robot Reprap
Rostock (which is pretty cool even with stepper motors). The sensors give a
resolution of 4096 ticks per rotation, and the controller can currently position the motors to within +/-2 ticks. They've also simplified the printer electronics by driving as much as possible from the controlling computer using
Bowler, a new communication protocol for machine control. The Servo Stock also includes sensors for the hot end, presumably to be used to control the filament feed rate and temperature. The hardware models are fully parametric, allowing reasonably straightforward scaling of the design. Source for the hardware, firmware, and software is
available.