Public Anemone

Inspired by primitive life, Public Anemone is a robotic creature with an organic appearance and natural quality of movement. By day, Public Anemone is awake and interacts with the waterfall, pond, and other aspects of its surroundings. It interacts with the audience by orienting to their movements using a stereo machine vision system. But if you get too close, it recoils like a rattlesnake.

Mechanical Design

The public anemone robot has 13 degrees of freedom: 8 body stages and 5 tentacles. Each body stage is rotated 90 degrees relative to the stage below. Servomotors at each stage allow us to fit all of the mechanical parts within the robot itself, avoiding problems of friction, control lags, and elasticity that would be introduced with external control. This gives the robot a broad range of motion with the ability to precisely control each stage. To avoid the effects of cumulative backlash from the planetary gearboxes at each stage, torsional springs preload each gearbox against one side of the backlash region. This permits a smooth quality of motion as shown in the movie.

Motor Controllers

Modified commercial servo controllers, using optical encoders to measure finger positions, control each of the finger motors. The eight stages of the robot’s body are controlled using a custom high-density motor control platform currently under development for use in robots with many degrees of freedom. The body motors are equipped with a combination of optical encoders and potentiometers, enabling both precise control and absolute position sensing.

Fabricating the Skin

The skin is made of a highly elastic silicone rubber and is designed to fit over the mechanics in a way that maximizes the realism of motion. To create the organic look and feel of this synthetic flesh, the exterior of the skin was first carefully sculpted in clay and then a four-part, lightweight syntactic mold with a plastic inner core was created. Pre-colored silicone and other additives to create the correct elasticity and opacity was then injected into the cavity between the mold and the core and allowed to cure. Finally the skin was trimmed, patched, and painted. This process is shown in the movie.

The high-level behavior of the robot is controlled by a system developed by the Synthetic Characters group at the MIT Media Lab. This system has been used to create graphical creatures that interact with and learn from people. We adapted it to the task of controlling a robot for this project, and used the animation capabilities as a simulator.

The motions of the anemone are based on handcrafted animations to give it a natural and expressive quality of movement. See movie.

The behavior engine blends and layers these animations to make the movement of the robot appropriate for the situation at hand. For example, the system blends together several animations of the anemone posed in different orientations to enable it to direct its attention to a particular person’s face. In the movie, these animations are blended to track the animated hands as a person controls them using a joystick.

The anemone starts each day’s cycle with a high confidence level and a desire to complete various tasks (such as watering the nearby plants, drinking from the pond, or bathing in the waterfall). It chooses to either continue its tasks or interact with a participant based on their behavior and how much progress it has made with its tasks. If a participant wins the robot’s attention, it will respond by orienting toward that person and following their movement. If a participant gets too close or makes a threatening movement, the anemone may become frightened and recoil from the crowd until it regains its confidence. See Movie (.mov file, 5770 KB). Because the robot makes decisions based on its internal drives and audience interaction, each day is different from the next but follows a coherent theme.