The Role of PCBs in the Delft Hyperloop Pod
We are Delft Hyperloop, a student team from the University of Technology Delft. With 40 students, of which 34 full-timers and 6 part-timers, we compete against other universities over the whole world in the 2019 SpaceX Hyperloop Pod Competition in Los Angeles, California. This is the third time that we participate in this yearly competition: last year (2018) we ended second and a year before we even won!
The goal of this year’s competition: design and build a vehicle that is able to achieve an as highest velocity as possible in a vacuum tube of approximately 1000 meters. Therefor, our pod uses eight electromotors with four high voltage battery packs. The pod is approximately 150 cm long and 60 cm width and with this vehicle we aim to reach half the speed of sound (617 km/h).
For the low voltage system, we designed three PCBs that are manufactured and assembled by Eurocircuits. This system has four responsibilities:
Contain and read all needed sensors (i.e. temperature sensors, pressure sensors, diffuse sensors and battery management systems).
Run a navigational algorithm to calculate the moment the pod has to brake.
Give control to other subsystems, like the braking and the propulsion subsystems.
Establish a wireless connection that allows us to read sensor data and to give commands from outside the tube.
One of the main challenges of this system is to determine the position and the velocity as accurate as possible. By knowing these parameters and knowing the brake distance of the pod, the maximum point to brake can be calculated without ending the run of the pod while crashing against the end of the tube. The velocity can easily be calculated with the encoders and the position with the odometer, both integrated in the motor controller. As mentioned before, two diffuse sensors are attached to the pod. These sensors are able to detect reflective tape stripes, which are placed in the SpaceX Vacuum Tube every 100 ft (approx. 30 meters). By counting the amount of passed stripes, we can verify the position of the pod.
To ensure the system will work perfectly, we divided the four responsibilities over four CPU development boards, of which the first three are from the Nucleo-family of STMicroelectronics. The last responsibility – the communication – was performed by a Raspberry Pi, connected to an Ubiquiti radio station and two antennas. These CPUs all communicate with each other over one CAN-bus, which is also connected to the Battery Management Systems of the high voltage batteries. A second CAN-bus is used to communicate to the motor controllers, which provide a lot of data needed for position and velocity estimation.
The thee custom-made PCBs will be placed as shield on top of each Nucleo CPU. Every PCB consists of LEMO connectors to easily connect the CAN-busses, the sensors and the actuators (i.e. the solenoid valves that are part of the braking subsystem). All these low voltage electronics are powered by two times a 3S2P low voltage battery pack that have a nominal voltage of 11.1 V. Besides the LEMO connectors, all other low voltage circuitry is assembled on these PCBs, like:
Battery Management Systems for the low-voltage battery packs, including fuses
CAN transceivers for both CAN-busses
DC/DC-converter to 5V to power the Raspberry Pi
DC/DC-converter to 12V to power all CPUs, sensors and actuators
DC/DC-converter to 24V to power the communication radio station
Digital isolator to isolate the signals to the motor controllers
Small ambient temperature sensor
Small ambient air pressure sensor
With these PCBs all subsystems can easily be connected and disconnected, which is very handy for testing purposes. Since the PCBs function as shield of the CPU development board, it is very easy to communicate with the CPUs and the rest of the system.
After a lot of work and testing, we are really looking forward to the 2019 SpaceX Hyperloop Pod Competition, which will take place on the 21st of July!