A Robot Tentacle with Big Doc Ock Energy
Trying to harness some big Doc Ock energy, James Bruton experimented with a robot tentacle built with Stewart platform joints.
Doctor Octopus, AKA "Doc Ock," is a pretty middling villain in the Spider-Man universe, but his onscreen rendition in 2004's Spider-Man 2 was memorable thanks to his mechanical tentacles. Those tentacles are very cool and we all want a set, whether we admit it or not. But while many have attempted to replicate the mechanical tentacles, their attempts never quite reach big Doc Ock energy. That's why James Bruton decided to take a unique approach and built a prototype tentacle using Stewart platforms for joints.
The benefit of a Stewart platform is that it can provide a lot of movement freedom in a compact and stable package. That requires six actuators, but they are able to move the top platform in any direction or tilt it at any angle. Stewart platforms can also handle a lot of weight, which is why it is common to see them supporting industrial machinery. Those factors make Stewart platforms a promising choice for the joints in a robotic tentacle; daisy-chain several of them together and you get a very dexterous appendage.
Bruton's prototype contains three Stewart platform joints, resulting in a tentacle around three feet long. Its entire structure, including the actuator arms, was 3D-printed. Only the base and the servo arm mounts are aluminum. Hobby servo motors handle the actuation by rotating arms that push hinged linkages. The angle of the servo arm alters the distance between the two platforms at the connection points, and the relative distances of all six determine the angle of the top platform relative to the bottom platform.
Each Stewart platform needs six servo motors and there are three platforms in the prototype, so this requires a total of 18 servos. That is large number to control, which is why Bruton chose to use an Arduino Mega 2560 with its many IO pins. That works pretty well and the arm moves smoothly with quite a lot of freedom. To get the full effect, Bruton would need to increase the number of Stewart platforms and the overall length.
Of course, that would be a challenge. Every joint needs six servo motors, which is a lot to control. And to support the weight of a full-length arm, the servos near the base would need to be very powerful. But the prototype is awesome and we'd love to see Bruton build a complete arm. Or, even better, four complete arms.
