Engineer Clay McPherson is building an open source compact boat-bot with a difference: designed to operate under solar power, the autonomous aquatic drone maps beneath the waves by plotting the depth of the water via sonar.
"It runs on solar power and autonomously follows a pre-planned set of coordinate waypoints based on live GPS and magnetometer data," McPherson explains of his creation. "I wrote the autopilot code myself, it doesn't use Ardupilot or a pre-existing flight controller. It has a Blue Robotics sonar module to plot the depth of the water as it goes. All the data is logged to an SD card in CSV format, I then create the 3D plots after the fact using [MathWorks] MATLAB to approximate a surface that intersects all the measured points."
Designed purely as a hobby project, the compact boat is driven by a Teensy 4.0 microcontroller connected to a u-blox NEO-6M GPS receiver, an RCElectricParts electronic speed controller, and a solar panel — described as "cheap eBay garbage" — linked to a Genasun GV-5-PB-12V charge controller. The idea: an autonomous boat-drone that can follow a set course to create a depth map of a body of water, using the Blue Robotics Ping Echo Sounder sonar module.
"[The boat is] consuming around 40W of power at full throttle," McPherson explains. "Its battery, charged by excess solar energy, can power the vehicle for around 40 minutes during gaps in solar access. It is driven by two brushless DC motors which are fully submerged, directly driving two propellers which I designed and 3D-printed to steer with differential thrust."
The data gathered by the boat is processed in MATLAB to create an attractive depth plot, representing the undulations of the ground beneath the surface of the water — though, at the moment, there's no compensation for waves causing undulations in the water too. "I’m mainly making these plots for fun and because it’s a great excuse for a complex project and learning experience," McPherson explains. "But I’ll definitely be using the data to find some nice deep pits for catfish/gar fishing."