Mapping Lakebeds with an Autonomous, Solar-Powered Boat

The value of bathymetry

Knowing the depth of a given sea or lake at various points can yield valuable insights into where underwater currents, certain marine life, and hidden coastal shelves might exist. But performing these measurements, also known as bathymetry, is time-consuming and labor-intensive- typically requiring the use of a boat and an accompanying crew. Last year, maker Clay Builds released an open source mapping solution, affectionately named the Gumption Trap, that could autonomously traverse a lake's surface and take periodic measurements. However, its small size and lack of serious motor power left it unable to overcome some of the stronger waves, leading to the second version: the Gumption Trap II.

Designing a watercraft

With the goal of extra stability and enough surface area for two large solar panels in-mind, this newer design features a pair of fiberglass pontoons on either side of the panels that extend for the entire length of the craft. At the rear of each one is a rudder assembly that can pivot thanks to a toothed pulley connected to a servo motor via a timing belt. Lastly, two 100W solar panels sit across the pontoons and provide structural rigidity as well as enough power to operate the boat indefinitely.

Propulsion and steering

A brushless 3-phase motor and propeller sit just behind each rudder to give the boat plenty of thrust when fighting the wind and waves. When making a tight turn, their ability to rotate at different speeds can help decrease the turning circle even further and improve mobility. The motors receive their power from two electronic speed controllers (ESCs) connected to a Teensy 4.0 microcontroller, and the current draw of the entire boat is monitored with a couple of Adafruit's INA260 current sensor breakout boards.

Autonomous navigation and measurements

Because the goal of this boat is to gather depth data across a body of water, knowing where the watercraft is and the distance to the sea floor at any one time with great accuracy are vital. In this case, Clay Builds went with a Ping2 Sonar Altimeter from BlueRobotics, as it can measure at depths up to 100 meters with a 0.5% resolution and easily interfaces with Arduino-compatible firmware. When it comes time to maneuver into position, the Teensy 4.0 gets its current location from the connected GPS module, reads the destination coordinates from the SD card, and then follows a course to the location aided by the magnetometer and tuned PID loop.

Analyzing the data

To test his creation in the real-world, Clay Builds launched his boat into the water with the aim of capturing location, depth, and heading data along with bonus points for autonomously navigating. At first, it seemed fine, but shortly after the GPS module would lose signal and cause the boat to run aground, ultimately resulting in an invalid depth map. Once the issues with the GPS module and some of the software are fixed, he plans on creating a follow-up to this initial test video where he demonstrates the full capabilities of his system.