Shapeshifters: Look ma, it’s a boat; What? It’s a bridge now

The project is led by MIT professors Daniela Rus, Carlo Ratti, Dennis Frenchman, and Andrew Whittle. Photo: Massachusetts Institute of Technology and the Amsterdam Institute for Advanced Metropolitan Solutions

In mythology and folklore, shapeshifting allows humans to transform themselves into animals or birds, aided by divine intervention or magic. The Massachusetts Institute of Technology (MIT), on its part, has applied science and upgraded its fleet of robotic boats with capability to ‘shapeshift’ into different floating forms.

In demonstrations in an MIT pool and in computer simulations, groups of linked ‘roboat’ units rearranged themselves from straight lines or squares into other configurations, such as rectangles and ‘L’ shapes. The experimental transformations took a only few minutes. More complex shapeshifts may take longer, depending on the number of moving units and differences between the two shapes.

The autonomous boats–rectangular hulls equipped with sensors, thrusters, micro-controllers, GPS modules, cameras, and other hardware–are being developed as part of the ongoing ‘Roboat’ project between MIT and the Amsterdam Institute for Advanced Metropolitan Solutions (AMS Institute).

The idea is to have the roboats cruise Amsterdam’s 165 winding canals, transporting goods and people, collecting trash, or self-assembling into ‘pop-up’ platforms such as bridges and stages, to help relieve congestion on the city’s busy streets.

Three years ago, MIT researchers tested a roboat prototype that could move forward, backward, and laterally along a pre-programmed path in the canals. Last year, researchers designed low-cost, 3D-printed, one-quarter scale versions of the boats, which were more efficient and agile, and came equipped with advanced trajectory-tracking algorithms. In June, they created an autonomous latching mechanism that let the boats target and clasp onto each other, and keep trying if they fail.

In a new paper presented at last week’s IEEE International Symposium on Multi-Robot and Multi-Agent Systems, the researchers described an algorithm that enables the roboats to smoothly reshape themselves as efficiently as possible. The algorithm handles the planning and tracking that enables groups of roboat units to unlatch from one another in one set configuration, travel a collision-free path, and reattach to their appropriate spot on the new set configuration.

The project is led by MIT professors Daniela Rus, Carlo Ratti, Dennis Frenchman, and Andrew Whittle. “We’ve enabled the roboats to now make and break connections with other roboats, with hope of moving activities on the streets of Amsterdam to the water,” says Daniela Rus, director of the Computer Science and Artificial Intelligence Laboratory (CSAIL). “A set of boats can come together to form linear shapes as pop-up bridges, if we need to send materials or people from one side of a canal to the other. Or, we can create pop-up wider platforms for flower or food markets.”

For their work, the researchers tackled challenges with autonomous planning, tracking, and connecting groups of roboat units. To enable smoother operations, the researchers developed two types of units: coordinators and workers. One or more workers connect to one coordinator to form a single entity, called a “connected-vessel platform” (CVP).

Coordinators come equipped with GPS for navigation, and an inertial measurement unit (IMU), which computes localization, pose, and velocity. Workers only have actuators that help the CVP steer along a path. During shapeshifting, all connected CVPs in a structure compare the geometric differences between its initial shape and new shape. Then, each CVP determines if it stays in the same spot and if it needs to move. Each moving CVP is then assigned a time to disassemble and a new position in the new shape. Using data from the GPS and IMU, the coordinator then estimates its pose and velocity at its center of mass, and wirelessly controls all the propellers of each unit and moves into the target location.

Experiments were conducted on quarter-sized roboat units, which measure about 1 meter long and half a meter wide. But researchers believe their trajectory-planning algorithm will scale well in controlling full-sized units, which will measure about 4 meters long and 2 meters wide.

In about a year, the researchers plan to use the roboats to form into a dynamic “bridge” across a 60-meter canal between the NEMO Science Museum in Amsterdam’s city center and an area that’s under development. The project, called RoundAround, will employ roboats to sail in a continuous circle across the canal, picking up and dropping off passengers at docks and stopping or rerouting when they detect anything in the way. Currently, walking around that waterway takes about 10 minutes, but the bridge can cut that time to around two minutes.

To reach that goal, the researchers are further developing the roboats to ensure they can safely hold people, and are robust to all weather conditions, such as heavy rain. They’re also ensuring that the roboats can effectively connect to the sides of the canals, which can vary greatly in structure and design.

Researchers have been working on developing shapeshifting materials for quite some time. However, such materials have historically been limited in size or extent and the object state changes have proven difficult to fully reverse.

Last August, though, the University of Colarado Boulder (CU Boulder) engineers said they have developed a material that can transform into complex, pre-programmed shapes via light and temperature stimuli, allowing a literal square peg to morph and fit into a round hole before fully reverting to its original form. The controllable shape-shifting material, as described in the journal Science Advances on 24 August, 2018, could have broad applications for manufacturing, robotics, biomedical devices and artificial muscles.

Similarly, last August, researchers from the Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS) said they have developed a mathematical framework that can turn any sheet of material into any prescribed shape, inspired by the paper craft kirigami (from the Japanese, kiri, meaning to cut and kami, meaning paper).

Unlike its better-known cousin origami, which uses folds to shape paper, kirigami relies on a pattern of cuts in a flat paper sheet to change its flexibility and allow it to morph into 3D shapes. Artists have long used this art form to create everything from pop-up cards to castles and dragons.