Excavator

Original is Volvo ec210
M about 1:20
And yes: there is sand at the teeth of the bucket out of my kids sandbox ;-)

I hope the pictures are descibing the project best. On pic SAM_4173 the lower part of the body is shown with holes for batteries. It was redesigned that a big pb battery fits now. The two servos in the arm have about 120 Ncm, the big one in the body about 260 Ncm.
In the tracks and for turnig there are the the cheapest servos ever in there for about 2,5€.
The servos in the tracks are hacked so that the pwm signal still works but they do it continously. Just search the web for "pwm servo hack"!
In the turnshaft i soldered the + and - of the servos togeter to reduce lines from 6 to 4.
The tooth gears are bought:
http://www.conrad.de/ce/de/product/297410/Zahnradsortiment-Modul-1
Maybe you can also print them, I can't.
You can use: http://www.thingiverse.com/thing:333018
The tracks are in fact a derivate from http://www.thingiverse.com/th