In 2017, Boeing and GoFly announced a worldwide competition to foster development of ultra-compact flying devices capable of flying 20 miles and carrying a single person.

Silverwing, a student team at the Delft University of Technology in the Netherlands, was formed to develop an electric aircraft to win the Boeing GoFly Prize.

These students imagined a future beyond roads ー a world where electric mobility is available on demand and unlimited in three dimensions.

Seven months ago, I attended the design reveal of the S1, Silverwing’s electric vehicle, and I was inspired by their vision for the future of transportation.

Shortly after, I joined the team as a Power Systems Engineer and I was tasked with working on the low-voltage electronic system.

At the time, I was wrapping up the first year of my Bachelor’s degree in computer science and while I knew the basics about electronics, I had never designed or assembled a printed circuit board myself.

The past few months have been packed with learning EAGLE and Altium, testing, ordering parts, analyzing datasheets, soldering, and getting to collaborate with motivated engineers.

Eurocircuits has greatly supported the advancement of our vehicle by allowing us to quickly order and receive high-quality PCBs. Often things do not go as expected. Parts break.

Requirements change. Our team needs to adapt to each new obstacle as quickly as possible, which is why we rely on fast and smart prototyping, something greatly supported by collaborating with Eurocircuits.

The S1 has a high-voltage powertrain that drives the motors and is powered by our high-voltage battery. We also have an entirely separate system for powering our low-voltage electronics.

These peripherals include all of our sensors, our flight computers, and our servos.

All these avionic devices are powered by our low-voltage battery and all feedback and control signals must be communicated to the flight computer.

This is what most of my work is centered around: designing and assembling PCBs to supply all required voltages to avionic devices and route all signals to their respective flight computers.

All the low-voltage PCBs are stored in the Electronics Box, which is housed on the body of the vehicle.

The vehicle currently contains six different low-voltage PCBs, all of which are the result of testing and a number of previous iterations.

Often, we test circuits using pre-made SparkFun Breakout Boards (mostly for testing PWM signal amplification or RS232 to TTL signal conversion) or on breadboards (used for testing CAN bus filtering) before implementing them in our designs.

Furthermore, some of the boards designed and assembled are “hat” boards that stack on top of existing PCBs or devices to add additional functionality, such as the BeagleBone Hat, which is a board that attaches to the BeagleBone Black in the aircraft (our companion flight computer).

One of the most important PCBs on our aircraft is the Signal Board.

The S1 is composed of a number of sensors that allow us to control, monitor and direct the aircraft.

Not-so-creatively named, its purpose is to route all control lines between the flight computer and the peripheral devices.

Such devices include our battery management systems, current sensor feedback lines, the feedback and PWM signals from our servos, an I2C bus for extra sensors, telemetry feedback, and the CAN bus for our motor controllers.

The Signal Board is a four-layer board: the top and bottom layers are used for routing traces, while the other two are designated 5V and GND layers.

On one side of the signal board are the wire inputs for the signal lines from our external peripherals (in blue).

The other side contains connectors for the signal lines that are connected to our flight computer and our companion computer (in red).

While the board partly serves to route signals without using messy external wires, some of our devices require additional filtering or signal conversion.

The signal board contains three SP3232EB ICs to translate serial RS232 signals from devices into TTL signals for our companion computer.

We also use a number of N-Channel MOSFETs to amplify 3.3V PWM signals from the flight computer to 5V signals for the servos.

One of the main challenges faced was interference and noise on the CAN bus: the bus in which both our motor controllers communicate with the flight computer.

This was partly solved in testing by shifting the location of the high-voltage power cables, but it was a problem we aimed to tackle on the second version of the Signal Board.

We tested out different filter configurations with 0.1μF capacitors and 11μH common mode chokes on bread-boards. While we had success with these filters, we still wanted the ability to swap out different filters on the new version of the Signal Board.

That’s when we had the idea of creating modular boards with different filters that plug into our Signal Board and allow us to alter the filters we use on the CAN bus.

These modular boards are similar to the shields you can buy for Arduinos, as you simply stack them on top of the Signal PCB.

Below (from left to right) are the three modules we designed.

The first is with no filtering, the second is with a common-mode choke connected to the CAN High and CAN Low lines, and the final is with the choke and two 0.1μF capacitors:

Here you can see one of our filters stacked on top of our Signal Board:

This is a bit of insight into the PCBs we are working on at Silverwing, as well as the challenges that we encounter while designing an electric aircraft.

Ultimately, our PCBs need to not only do their job, but also be robust enough to survive flight. At this stage, we are still testing and preparing for the final Fly-Off in San Francisco in February.

This is a bit of insight into the PCBs we are working on at Silverwing, as well as the challenges that we encounter while designing an electric aircraft.

Ultimately, our PCBs need to not only do their job, but also be robust enough to survive flight. At this stage, we are still testing and preparing for the final Fly-Off in San Francisco in February.

If you want to learn more about Silverwing and what we’re up to, check out www.flysilverwing.com!

Brontë Kolar
Power Systems Engineer at Silverwing