Vert-X-Belt-Truder

Early concept for a fully symmetric belt-driven extruder carriage for upgrading Prusa Mendel. Belt-driven means there's no stepper motor on the X-carriage, so it can be much lighter and move much faster.

It has two X-belts that are controlled by one stepper on each side.

If both belts move in the same direction, the X-carriage moves in that direction too. If both belts move in opposite directions, the extruder moves but the X-carriage stands still.

x_motion = (stepper1 + stepper2) / 2
extruder = (stepper1 - stepper2) / 2

We'll need new firmware to control x_motion and extruder independently by setting the correct speed for each stepper motor for the two belts.

stepper1 = x_motion + extruder
stepper2 = x_motion - extruder

This design attempts to reduce the effects of the torque that's required to move the extruder:

• It is based on the excellent VertX (vertical x-axis) by watsdesign with LM8UU linear bearings: http://www.thingiverse.com/thing:10711
• It uses a pretty large timing belt pulley on the back of the carriage.
• The two belts are entering the carriage very close together and perfectly parallel.