Mini Extruder with 3 Gears

This is a 3Gears extruder, My first extruder design, other extruder usually has one motot gear and one driver gear ,with big volume .I am trying to put 2~3 extruders on a printrbot Plus ,so a smaller extrduer will be needed , and i try to DDIY (design and do it myself) ^__^.

683zz bearings *2
608zz bearings *3
M8 hobblted screw *1
and some m3 screws


2014/1/27 update :improve the inside space to make the hobblted screw working better. And some gay said he dosn't has 683zz bea