KTH Formula Student

by Carolina Hållenius, Junior Product Specialist

KTH Formula Student is a project at KTH – the Royal Institute of Technology (Kungliga Tekniska högskolan) in Stockholm, Sweden. The project is about developing a driverless, electric race car. NCAB Group Sweden sponsors the project with PCBs.

Why is this project of interest for NCAB?

“NCAB strive to fill up with new expertise in the field of technology and hence a broad recruitment base is needed. We want to attract all young people regardless of who you are and where you come from, both to encourage young people’s technological interest and at the same time raise awareness about an industry that is not very well known among young people in Sweden today. We think that KTH Formula Student is a good initiative that fits well with our goal,” says Rikard Wallin, Managing Director NCAB Sweden/Vice President Nordic.

The future of e-mobility

KTH Formula Student was founded in 2003. The project aims to empowering students to engineer the future of e-mobility.

We asked some of the participating students about the project and their parts and responsibilities.

Robin Wikström, Project Manager during 2020:
“KTH Formula Student is all about learning how to apply the theoretical knowledge that we gain in school. It´s an ambitious project where students all over KTH gets involved in every part necessary to develop a race car. This includes things like marketing, management and design. Our work then gets evaluated by industry experts at competitions all over the world, testing both our engineering skills as well as the cars’ capability through static and dynamic events respectively.”

Kim Strinnholm and Jordi Altayó are doing their master in Vehicle Engineering and Embedded Systems, and their roles in the project are Technical Head of Powertrain and Technical Head of Electronics. They work with the electrical and electronic systems of the car which includes the electric drivetrain, high voltage battery, BMS (Battery Management Systems) and all the electronic circuits related to control and safety systems.

Tell us more about the motors and inverters in addition to the battery.

“To the car we are building for the competitions in 2021 we are buying a motor and inverter kit from AMK motors specifically optimized for Formula Student projects. It is a drivetrain consisting of 4 synchronous permanent magnet hub motors with a maximum power output of over 80 kW, driven by 4 individual motor controllers with an efficiency of around 98 %. To control this high power-outputs, and achieve as good performance as possible on the track, we are developing our own torque vectoring and traction control logics.”

What type of PCB do you design? How do you design? What programs do you use?

“Most of our PCBs are two-layer boards with a relatively low complexity. Usually a microcontroller-based board with additional discrete components to fulfill a particular functionality. Additionally, the competition rules force us to design certain systems without the use of programable components such as microcontrollers.

Our design process starts by establishing all the requirements and functionalities that the electronic system should accomplish as well as the interaction among different systems. Following that, all systems are designed by starting with the schematics and continuing with the PCB design. Every step in the design process is accompanied by a review phase where more experienced members or external collaborators reviewing the work that has been done so far. The final step in the process is the test and verification of the particular system before it goes in the car for final verification.

Our main program for PCB design is the KiCAD suite, an open-source PCB designing tool that is easy to learn and offers all the features that we need.”

Carolina Hållenius, Junior Product Specialist at NCAB Sweden about the PCBs that NCAB are contributing with:

“KTH Formula Student are going to compete in the 2021 Formula Student race. They have since the last competition come a long way in their product development process. The prototype phase is starting to reach its final stage and NCAB will contribute with sharp PCB’s, which mainly consist of different types of 2 layer boards but also including one 8 layer board.

The 2 layer boards will both have control over the electrical systems and the BMS system of the car. The specification of the 2 layer boards is 1oz copper, HASL and the panel size is under 100 x 100mm. The 8 layer board on the other hand is a high currency board which needs high copper weight, up to 6oz copper with HASL. The panel size will be around 100 x 200mm.

The project has divided their PCB into three major groups:

  • High Voltage (over 60V) – 8L
  • Low Voltage (less than 60V) – 2L
  • Battery Management System (BMS) – 2L

The high voltage area will include the 8 layer board which shall fulfill requirements such as galvanic isolation or use of non-programmable logic only. It focuses on safety aspects in the design to make sure that all fault safety does not damage the driver or personnel. They have chosen to divide the high voltage area into two parts:

  • Tractive System Active Light (TSAL). This system should in short send a visual signal by flashing a bright light if there is a risk that high voltage is active in the car. If there is no high voltage, a bright light will flash solid green.
  • The precharge is a controlled machine in BMS. The main thing about the precharge is to ensure a slow charge of the DVC connection by connecting it through a resistor during start up to avoid high inrush which can damage both capacitors or the battery.

The low voltage is one part of the 2 layer board areas which includes the data acquisition for vehicle measurements and the dashboard for the driver to monitor the state of the car as well as make adjustments to the vehicle behaviour. This part controls the effects such as torque vectoring, traction control and regenerative braking. The data collection consists of three modules:

  • DCU (Driver Control unit) includes parameters for the driver’s steering angle, brake pedal and throttle pedal.
  • VMU (Vehicle measurement unit includes parameters for wheel sped, suspension travel, tyre temperature and brake temperature.
  • AVMU (Auxiliary vehicle measurement unit) includes parameters for strain gauges for suspension mounting points, strain gauges for aero mountings and torque encoder for the steering wheel.

Battery management System (BMS) is the other part of the 2 layer board areas. This area monitors the battery status to measure the volts and temperature of all cells in the car to ensure that all systems in the car maintain the correct range of volts and temperature specified by the manufacturer. This will work in the front dashboard through an LED light to communicate to the driver if errors occur in the car’s various systems. This also includes various additional features that allow the driver to control everything with their hands through the screen menus at the wheel, torque, vectoring and navigation.”

We continue with Kim Strinnholm and Jordi Altayó:

What are your toughest challenges?

“Coordinating a team of over 100 people and make sure everyone is working towards the same goals and ensuring that we have a good communication within the team is challenging!

When it comes to technical challenges the high voltage battery is the most complex system in the car since it involves a fairly large multidisciplinary team with expertise in mechanical design, composite materials, powertrain simulations and electronic design. All the work has to converge towards a unique design that integrates all the functionalities required both by the competition rules and our internal requirements and goals, such as weight and sustainability.”

What is most important to your design? What just has to work?

“Some key components for our design and the work in Powertrain and Electronics, is traceability and documentation. This means we need to clearly motivate and document our design choices. This is mainly due to two reasons: we need to motivate and defend our design choices at the competition as part of the assessment of the car and when new members take over old projects, they need to have proper documentation to lean on.

In terms of most important system in the car it is of course the safety system, ensuring a safe operation of the vehicle and the high voltage system of 600 volt. This includes everything from safety interlocks to the safety state machines in the main control unit, which is monitoring everything that is of importance for a safe operation, but above all the isolation in the car. The BMS system for the high voltage battery is another crucial safety component that is part of this overall safety system.”

From a sustainability perspective, how do you make your car more efficient? What categories do you compete in?

One of the core values within our team is sustainability, which is permeating all the development. Everything from material selection to tuning the drivetrain have sustainability as an evaluation point when doing the choices. This is why we, for example, are having the efficiency event as one of our main goals, with a lot of focus on the regenerative braking strategy to have among the lowest consumption during the endurance race. This is also why performance parameters such as rolling resistance, drag coefficient and weight are important to us.

For the last 10 years the KTH Formula Student project has competed in the electric classes. Since last year, we´re also competing in the driverless class with the concept of being able to transform the car from electric competition to driverless with all the extra actuators, sensors and computers needed. We are among the only teams doing this, since the normal procedure is to have two different cars. By doing this we are using our resources much more efficient and we are having a more sustainable approach to competing in several classes.”

A final comment from Carolina Hållenius:

“KTH Formula Student is a welded team that has high ambition and addresses the challenges they face in developing a sustainable electric and driverless racing car.

Their goal is to get among the top five teams in Formula Student. We want to do everything we can to fulfill their goal. We will therefore contribute with our long experience and knowledge of PCB’s. By contributing with reliable, quality-assured and sustainable PCB’s, we will be able to build a strong relationship with the team to understand their PCB portfolio to finally take our full responsibility to deliver PCB’s according to the KTH Formula Student target image.”

Read more on the project´s website