This video documents the multi-year development of a novel hydrofoil height control system. The project's goal was to create a hydrofoil mast from a printed circuit board (PCB) with an integrated water level sensor, intended as a more direct alternative to traditional sonar systems. The initial approach using resistive sensing proved non-viable due to long-term electrochemical corrosion, which caused signal drift and physical degradation of the sensor traces. The project pivoted to a capacitive sensing method, which allows the primary sensing electrode to be fully insulated from the water, thus preventing corrosion. This was achieved by leveraging fringe field capacitance. After several hardware iterations, which included adding an ESP32 microcontroller for Wi-Fi configuration, a critical software bug limiting the PID control loop's update rate was identified and fixed. The resulting system demonstrated fast, stable, and autonomous altitude control on a test boat, leading to the creation of a commercial kit.
Developing an Autonomous Hydrofoil Control System
0:00 The Problem: Existing electronic hydrofoil height control typically uses sonar. The project's goal is to create a more integrated solution where the hydrofoil mast itself can directly sense the water level.
0:54 Initial Concept: Resistive Sensing: The first idea was to use simple, cheap resistive liquid level sensors integrated directly onto a PCB that also serves as the hydrofoil mast. An initial prototype demonstrated that the concept was functional and had a fast response time.
3:15 The Fatal Flaw: Corrosion: An electrical engineer, Tamas, identified a critical issue with the resistive design: electrochemical corrosion. Running DC current through exposed metal traces in water causes them to degrade, leading to signal drift and eventual failure. This makes the design unsuitable for a reliable product.
5:09 The Pivot: Capacitive Sensing: The team switched to a capacitive sensing design. By measuring the change in capacitance as water (a high-dielectric material) displaces air, the water level can be determined. Crucially, this allows the positive electrode to be completely insulated from the water, eliminating corrosion. The breakthrough was realizing that fringe field capacitance was sufficient, with the positive and negative plates on opposite sides of the PCB.
8:18 Real-World Testing: A simple trifoiler test boat was constructed to test the prototypes. Initial on-water tests failed; the boat was unstable due to an extremely slow and jittery servo response, indicating a problem in the control loop.
11:00 Debugging and a Critical Bug Fix: To diagnose the issue systematically, Tamas built a test rig using a repurposed 3D printer. He discovered the PID control library was only updating at 10 Hz by default, not the intended 100 Hz. Fixing this software bug was the key to unlocking performance.
11:46 Successful Foiling: With the PID loop running at the correct speed, the servo response became fast and smooth. The boat was now able to foil stably and autonomously, even with hydrodynamically inefficient square-edged foils.
12:39 System Refinement: The system includes a web server hosted on the onboard ESP32, allowing for easy configuration of PID values and servo endpoints via any Wi-Fi device. Physical refinements like sharpening the foil edges and waxing the mast further improved performance.
15:00 Production: The project progressed to designing a programming and testing fixture for mass production, indicating the transition from a prototype to a commercial product.
16:02 Product Availability: The final PCB hydrofoil kits are now available for purchase.