Senix ToughSonic Sensors Used in Hydrofoil Control on Solar Powered Boat

Senix: Tecnico Solar Boat is a university project consisting of cross-degree engineering students from Instituto Superior Tecnico, the major engineering university in Portugal, that work together on the development of boats powered by renewable energies. Their main purpose is to participate in worldwide competitions. In 2019 they participated in the Monaco Solar & Energy Boat Challenge and finished in 2nd place.

This year there were no competitions due to COVID-19, so they decided to do their own event and challenge themselves with a tour of Portugal, Odisseia 2020.

Odisseia 2020 consisted of 4 journeys: one in Douro river, one in Tagus river, one along the natural park of Arrabida, and a final one along the southern coast of Portugal, in Algarve.

The goal of this event was to show the vessel to the public and put all Tecnico’s work to test. They had a lot of improvements done during the 2019/2020 season, and one of them was thanks to a Senix ToughSonic 14 sensor to monitor the electronically controlled hydrofoils.

Hydrofoils allow a boat to get elevated over the water line in such a way that the hull does not touch the water. This is one way of reducing the drag forces exerted on the boat, thus allowing it to consume less energy for the same speed. Tecnico has been working on the implementation of hydrofoils since the beginning of our project (in 2015) and they finally made it happen.

To maintain a stable and level flight, the hydrofoils' angle of attack must be adjusted in real time. These adjustments must be precisely calculated, and for that a controller must be designed. This controller then uses data from sensors strategically positioned on the vessel, as shown in figure 2.

To calculate the adjustments, the controller uses different state variables, and each one of these variables must be estimated in the most precise way possible. Tecnico uses an AHRS to estimate 6 of the 7 state variables needed to control the boat but the 7th state variable is obtained using the Senix's ToughSonic 14 Ultrasonic Sensor. The sensor is used to measure the bow's distance to the water line. These state variables are:

• distance to the water line
• pitch
• pitch's rate of change
• roll
• roll's rate of change
• vertical speed
• horizontal speed

The controller combines seven state variable and applies its optimal state feedback gains to the state vector to find the right angle of attack of the hydrofoils.

The control system's hardware configuration can be seen in figure 3. The system has a main microcontroller which communicates with all the sensors and has the foil's controller coded into it. Every 50 ms the microcontroller updates its calculations of the angle of attack of the hydrofoils and sends this to the stepper's motor controllers that directly move the hydrofoils.

This was a great challenge, and the results were very successful, the team managed to make the vessel fly in different kinds of conditions: with ocean waves, river currents, windy conditions, etc. In all these conditions the controller proved to be very robust, and it could not be possible without Senix's ToughSonic 14 sensor.

Figures 4a and 4b shows the vessel flying during the Odisseia 2020 event, and figure 5 shows data acquired during one of the journeys of Odisseia 2020. The data shows the vessel flying at cruise speed, 7 m=s, at a height of 50 cm, with a pitch always close to zero and small oscillations in roll, this is maintained for 300 seconds, so 5 minutes. The deflections of the left and right foils can also be seen.