Revolve NTNU is an independent student organization at the Norwegian University of Science and Technology that consists of 64 team members working toward a common goal: to develop and build a racecar to compete in one of the largest engineering competitions in the world, Formula Student. This is their experience working toward the 2017 competition thus far.
We are always pushing the limits for our automotive design, and testing of our design is essential for ensuring performance during competitions.
The team uses a wireless telemetry setup in order to have easy, real-time access to our data. Revolve NTNU has experimented with multiple different technologies over the years, and used Wi-Fi for our 2016 system.
For our 2017 telemetry system, we were looking for an additional radio system using a lower frequency than either Wi-Fi 2.4 or 5GHz. We contacted Silicon Labs and saw that they had offerings that combine sub-GHz frequencies and low power, an added benefit for a battery driven racecar. Silicon Labs has been an excellent ally in our project, providing chipsets and development kits, in addition to being able to provide help with our questions.
The latest model, Gnist, powered by the Silicon Labs EFR32 Flex Gecko
The intended use for the module provided with use of an EFR32 Flex Gecko is to transmit mainly the most important data from the car to the base station. As our car uses a self-made battery, there are a number of safety precautions in order to ensure safe usage of the car. The most important, therefore, is the state of each individual cell in the battery. If the temperature is too high, the car is will automatically stop. We want to know the state of the battery from where we are in the pit so we can warn the driver to slow down in order to reduce the temperature of the batteries before the car shuts down.
The sub-GHz link provided by the EFR32 Flex Gecko is therefore required to provide an interference-free and longer-range alternative to the Wi-Fi system we used previously. We are also going to use the system to only broadcast the battery information to prevent problems maintaining the line as experienced with the Wi-Fi system. Other possibilities for the EFR32 include updating and tuning the car over-the-air by sending updates to the car wirelessly.
Check out the Gnist riding on Trollstigen, Norway’s most famous national tourist car routes:
Revolve NTNU has designed a custom circuit board using radio board inserts provided by Silicon Labs, greatly reducing the complexity, while maintaining the performance needed for our system. We are aiming for a range in excess of 500 meters with a bit rate of 500 kbit/s