I found this design while browsing on Internet and pretty liked it. So I decided to make a printable version of it. Must say it works very well.

All parts are connected with 3mm pegs. The holes in the long arms are little bit smaller so the peg will not fall out. I wanted to run the gripper with a small stepper motor from the old cd-rom drive, but the motor was to weak. So I redesigned the motor mount for the 6V DC motor I bought in local electronic parts store.

Before printing please read the instruction page.

To print:

1x Robotic gripper base
2x Robotic gripper jaw
8x Robotic gripper arm
2x Robotic gripper arm small
1x Robotic gripper center
1x Robotic gripper DC motor mount

Other things you will need:
1x 3mm screw 45mm long
1x coupler to couple motor shaft and 3mm screw
1x 3mm Rivet nut (http://www.rivetsonline.com/rivet-nuts-and-threaded-inserts.html) or make your own on lathe.