Drawing on the experience from Paragon, we are striving to create a more sophisticated electrical system for GaAsoline. We are adding new functionality and compatibility while trying to maintain the reliability achieved in previous cars. Progress and ideas for the major components follow below:

Main Node

The Main Node is the control center for the entire car. It communicates with the motor controller, power trackers, driver interface, battery pack, and the telemetry computer. The Main Node’s architecture has been completed and will be featuring Microchip’s 18F2680 microcontroller. This computer is more powerful than Paragon’s was since it will be required to process and export more data than ever before. This increased performance will pay off during the race as we will have more information streaming from the car to aid with strategy.

Recently, hardware layout has been completed and, thanks to our sponsor Advanced Circuits, it has become a tangible reality. Improving our design over cars of the past, this board is smaller and more compact than before. We decided to incorporate some surface mount parts to help reduce the board size and give us some experience with surface mount devices and techniques.

The final program build for the main node is yet to be done. This is usually one of the last steps to be done as the programming will undergo constant tweaking. New ideas are always coming to mind, such as “Why can’t we have an odometer in the car? We have EEPROM.

Array

The array on our new car is comprised entirely of Gallium Arsenide cells from Emcore Photovoltaics. (This is where the name GaAsoline comes from- the chemical notation for Gallium Arsenide is GaAs.) These GaAs cells are much more efficient than the A300 silicon cells used on Paragon. Paragon’s array was getting an estimated 16% efficiency, where we expect better than 22% from GaAsoline’s array.

The process of preparing the cells for the array is a long and labor-intensive task. There will be about 2200 solar cells included in the final array and each cell must have three tabs and a diode attached by hand before it can be sorted and soldered into a module. The Array team has already finished tabbing approximately 2700 cells (necessary cells plus lots of spares) and is currently in the process of attaching all the diodes. The diodes act as a failsafe device, allowing current to pass around a broken cell. Without the diodes, one broken cell would knock out an entire module- about 40 cells- resulting in a worrisome loss of power.

Ideas for protecting the solar cells and adhering them to the car have not yet been finalized. There are two processes which work well for attaching the cells to the body - encapsulation and conformal coating. Encapsulation is a process of sandwiching the cells between protective layers (it looks like thick lamination) and then essentially gluing the section down to the car body. Encapsulation provides protection against dust as we are working on the body and other cells, but it is a very time-consuming operation. Conformal coating is done by laying the cells down directly on the body and then spraying over a clear coat. This gives better aerodynamics than encapsulation, but it has the potential of being heavier. Conformal coating also does not allow for damaged cells to be removed and replaced because they are permanently adhered to the car body.

Battery Pack

GaAsoline's battery pack will be comprised of Lithium Ion cells which are similar to Paragon’s batteries. These Li-Ion cells are the same size as our older batteries, but have 13% higher energy capacity. GaAsoline’s pack will also be 5kg heaver than Paragon’s because this car is being designed for the updated rules of WSC. Higher energy capacity per battery combined with a bigger battery pack means we will be able to store much more energy in this car. We will also be running at 147 volts instead of Paragon’s 108V. The reason for this higher voltage is to close the voltage gap between our array and battery pack, and also to support a high motor speed.

This pack will be sporting measurements of voltage at every module, temperature at select critical points, and current on the main leads to the pack, all of which can be used to monitor the status of the batteries. The battery protection circuitry can shut down the pack if any of the batteries exhibit behavior outside tolerances. Our team has not had a battery pack failure and we intend to keep it that way. Through careful design, construction and monitoring, we plan to have another successful run with the Lithium Ion chemistry.

A how-to has been written on out battery modules. Check it out here.

Power Trackers

GaAsoline will be utilizing an evolution of the Buck Maximum Power Point Trackers (MPPT) found on Paragon. “Buck” means the voltage from the array will be dropped down to match the battery pack and motor controller.

Propulsion

This build will be sporting a whole new motor controller and motor. We are currently in the process of designing our own motor casing to fit our application. More information on this can be found here.