Vertical Movement of the Head
One of the ways the octopus dances is by moving its head up and down. When it is not dancing however, the head ducks down and moves horizontally to watch as people pass by. This was achieved by making an isolated system mounted on a turntable.
To include vertical movement, a servo drives a crank slider when the octopus is confident to dance. The servo rotates between 270 degrees and 0 degrees back and forth to move the slider up and down. The structure is also secured by elastic tension to reduce interference and overcome unaccounted friction from the materials.
The crank slider system is mounted to a gear resting on a rolling turntable. This gave the octopus sufficient support and clean horizontal motion. The gear is attached to another servo that activates when a passerby gets too close. That servo drives a gear connected to the rolling turntable driving the system.
The design had to balance making the head go up and down with a noticeable distance and making the box as small as possible so as not to interfere with the servos inside the box (seen below). Iterations went through reductions in spacers and stabilizing features to optimize the space being used.
The material we settled on for the box itself was 3mm MDF because of how light it is and its high accessibility. The crank slider arms were originally cut from the same MDF, but because they frequently broke, replacements were made from acrylic plastic for less fragile material.
The octopus head, though only made of paper mâché, proved cumbersome for the small support coming from the top of the box. Our final design of the head support was made taller and included space to add parts that would reach outward within the head to provide additional support.
Above is the final design for the crank slider box. The 2 walls were removed to make for easy access to the internal design. The head support in this image is the shorter version to fit the image. The design of the final support can be seen in the next image above. The holes were included to screw together the servo mount on the side, and the turntable gear to the bottom.
In the image on the left, there can be seen a piece of metal support attached to the ceiling of the box. That was included to restrict horizontal movement of the head support and to keep the servo from rotating too far.
Rotation of the Head
In addition to vertical up and down movement the head also rotates. This system involves 2 gears, one motor, and a lazy Susan turntable. The turntable is mounted to the bottom of the box. On the top rotating piece a large gear and the head box are secured. A motor attached to the right wall (when facing the front of the box) powers a smaller gear. This gear interlocks with the other gear and turns the head. The gears are 8.4cm and 9.8cm in diameter. The tooth ration is about 2:1 and allows the box 180 degrees of rotational freedom. The gears were 3D printed with PLA and 3M heat sets were used for attachment.
A problem came up in the testing phase. The smaller gear attached to the motor was angled. After checking the make sure the motor and motor mount were level, the only answer was that the adapter from gear to motor was not level. After further inspection the adapter had bent during initial attachment. A new adapter was made and secured with a larger screw. The issue was resolved with that replacement. The gears work well and provides full functionality.
Gear CAD
