A robotic arm with 2 degrees of freedom (DOF) controlled by 2 servos and an arduino. Fishing line (or extruded plastic threads) acts as tendons and a spring at each joint allow the arm to curve evenly.
This project is a stepping stone to a larger project, so it is not meant to do anything useful yet, but be used as a part of whatever you can come up with.
To build it you will need to print one tentacleBase.stl, one tentacleJoint1.stl, two tentacleJoint2.stl and three of tentacleLink.stl.
To assemble the parts, the base and links attach to the joints using a piece of 3m filament inserted into the side of the joint and through the link (hopefully the pictures will help this make sense).
Joint 2 attaches to the base then alternates every other joint with joint 1. If the joints aren't lined up in the proper order, then the spring hooks and tendon holes won't line up along the length of the arm.
To attach the servos, the holes in the base may need to be enlarged slightly and the servo should press-fit into place.
To tie on the tendons, first tie one end to the end of the arm (this could be the end of a link or the side of a joint), thread it through the holes in the joints then through the routing holes in the base.
To tie the tendon to the right length lay the arm out straight and angle the servo horn (oh yeah, you'll want to put those on so they move fully forward and backward relative to the arm and swing to the outside so they don't hit each other) so it is slightly further toward the arm from the half way point and then tie the tendon the the end of the horn so it is taut.
Next, attach the springs (I got mine from a generic assorted bag of springs) or elastics to the anchor points. When the servo is in the middle point the arm should be (mostly) straight, if not you may want to adjust the tendons.
All that is left to do is hook it up to a microcontroller and have it move around.
Also, for those who want them I have attached the NX6 prt files in a zip.