- hydrofoil control sensor, RS-485, SenixVIEW, ultrasonic sensor, water level sensor
The solar-powered boat designed and built for competition by a team of students at Delft University of Technology in the Netherlands depends on Senix ToughSonic 14 ultrasonic sensors to keep the craft at just the right height above the water. The boat uses hydrofoils that lift the hull out of the water to reduce the drag so it’s propelled more efficiently. Using the hydrofoil design presented the students with two major challenges—how to keep it stable and at the right level above the water. The students solved the sideways stability problem by designing the boat so it can be steered like a bicycle.
Watch the video (it’s in Dutch, but it’s cool and there is a transcript):
Ultrasonic Sensors Measure Distance Over Water
They solved the water level measurement challenge by mounting ToughSonic14 ultrasonic sensors on the bow and stern of the boat to continually measure distance to the water. “By sensing the height above the water on the bow and stern of the boat, we can verify our dynamic models,” explained Gijs Bruining, the Delft University student with lead responsibility for electronics and data acquisition. “Because we are using a very new concept of hydrofoil configuration, we are very interested in the dynamics of the system.”
Sensor Integration Was Critical
The team configured the Senix ultrasonic sensors to use digital RS-485 output to communicate with a microcontroller. “The data from the ultrasonic sensors are converted to controller area network bus (CAN-Bus) frames, which are logged together with all other signals on the boat,” Bruining said. “The CAN-Bus data can be read in real time by the pilot. The data also can be read out live by a 3G connection with a server in Delft.”
The bow ultrasonic sensor controls the angle of attack directly via a proportional-integral-derivative control (PID controller). “The pilot sets a desired height on the steering wheel,” Bruining said. “The PID controller calculates the current error and then calculates the proper angle of attack.”
The ultrasonic sensor on the stern of the boat provides data that establishes the attitude of the boat and the responsiveness of the level control system at the bow. This data is being collected to help drive refinements in future boats.
SenixVIEW configuration software has played an important role in the project. “We’ve used SenixVIEW to configure the sensors to a higher update-rate and a moving average filter to eliminate the impact of waves and splashes on the readings,” Bruining said. “We also found it very convenient to be able to test the sensors without having to connect them to the rest of our system. This allowed us to verify the working range without having to implement all the communication aspects first.”
Hydrofoiling Drive Train
The solar boat is driven by a brushless direct current motor at a nominal voltage of 44.4 volts. The motor is mounted inside the boat just behind the driver and is connected to a driveshaft through the back strut. The propeller is driven using a 1-to-1, 90 degree transmission. According to Bruining, the boat has achieved a top speed of more than 45 km/h (27 mph or 24 knots).
ToughSonic Sensor Reliability
“The ultrasonic sensors have been working flawlessly,” explained Bruining. “We are really impressed with how reliable they are. We built an IMU (inertial measurement unit) as an automatic backup, but we’ve never had to use it.”
Bruining also credited the ToughSonic ultrasonic sensors for their ruggedness. “During races, the sensors are always exposed to the elements, but even after a recent race in Monaco where they were exposed to salt water, they didn’t suffer from any corrosion,” he said.
Bruining said that in the coming academic year, students at Delft University are planning to design and build a completely new boat to participate in competitions. “If the next team chooses to use an electrical height control system, I will certainly recommend they use Senix ultrasonic sensors.”
See how Oracle Team USA also uses ultrasonic sensors to control hydrofoiling in The Americas Cup.