Autonomous Robot Grows Stem by Responding to Light and Gravity

Researchers in Italy have developed a remarkable robot that mimics the growth patterns of a plant. Known as FiloBot, this innovative creation is the result of the Bioinspired Soft Robotics Laboratory at the Fondazione Istituto Italiano di Tecnologia in Genova.

FiloBot constructs its own stem-like body, which can reach several meters in length. It permanently curves in response to light, darkness, or gravity, and it can adjust the strength of its body based on its environment.

The robot consists of three main parts: a 40mm diameter head, a body of the same diameter, and a base unit. Initially, the head sits on the base unit without a body.

Growth begins when the head starts rotating and deposits a thin stream of melted plastic from a point on its edge. This plastic hardens into a circle, and ring after ring is deposited in the form of a continuous spiral. Gradually, the body is formed, lifting the head layer by layer.

The head of FiloBot is a marvel of miniaturization. It contains two motors with drivers, a rotation mechanism, a deposition mechanism, a Bluetooth microcontroller, a three-axis accelerometer, and a color sensor. The Bluetooth is used for telemetry and debugging purposes, as the robot operates autonomously. Its growth is emergent, without pre-planning or external guidance.

The body of FiloBot was grown in the lab and then placed around a tree for fun. The robot can be steered by depositing more or less plastic at different points during its 360° rotation. This variable deposition technique is also used to strengthen the body when crossing gaps or to be resource-frugal when support is available. The longitudinal growth rate is between 2 and 7mm per minute.

The motivation for steering FiloBot is similar to that of a plant, relying on gravity perception and the levels of blue, red, and far-red. Various algorithms are assessed by comparing the resulting growth with real plants. So far, the robot has demonstrated twining, gravitropism, phototropism, and skototropism.

To rotate the head, FiloBot has a short sleeve inside the body with springs around it that push outward. The ends of the springs are shaped to resist slipping circularly inside the hollow body while easily sliding longitudinally as the body extends. Teeth cut into the inside of the sleeve mesh with a gear on the end of a motor fixed to the spinning part. Another motor hauls 3D printing filament up the length of the body from a spool in the base unit, pushing it out through the deposition nozzle via a heater that melts it.

All of these components, including the electronics, are compactly packed into approximately 42cm³ and 82.5g. To prevent the plastic feed filament from tangling, the storage reel inside the base unit sits on a freely-rotating joint. Two wires pass up the inside of the body, supplying power to the head via slip-rings built into it. Cooling air for the head is provided by fans in the base unit.

The Fondazione Istituto Italiano di Tecnologia collaborated with the University of Montpellier, France, on this project. The research is covered in a highly interesting and readable paper titled "A growing soft robot with climbing plant–inspired adaptive behaviors for navigation in unstructured environments," published in Science Robotics.