Made this digging mechanism for my robot tank toy project(http://www.thingiverse.com/thing:687676). With this addition the robot platform can be used as nice construction toy for kids. Motors can also be added and the whole thing can also be used as a remote-self controlled digging robot.
I've used the image gallery of the project by tc_fea to create the model (Thanks buddy, http://www.thingiverse.com/thing:32394). I didn't download or use the STL files at his project as they wouldn't be the right size for my toy robot and i wanted to make a bit stronger digger, so I've used the mechanism but the size and details of the model are different.
Simulated it on solidworks, it works smoothly.