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As of 2016, the American Solar Challenge does not hold a separate class for Cruiser vehicles but does recognize them and provide special rules for them. It is possible that in the future Cruiser vehicles will have their own competition category in ASC.
Frame Design: Chassis & Body
Building a solar car requires extensive design to be put into the vehicle's chassis and body. These terms are used in automotive engineering and are described below:
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Midnight Sun's MSX was designed with a steel space frame, whereas MSXI was designed using a carbon fibre monocoque.
Solar Car Powertrains
A vehicle's powertrain encompasses everything that generates power and propels the car by transferring it to the wheels. In a traditional gasoline automobile, this means the engine, gearbox, drive shaft (if present), differential, axles, suspension, and wheels. Solar cars, as electric vehicles, forego the engine, gearbox, drive shaft, and differential, since most solar cars use electric motors that directly mount behind the wheels. However, solar cars must have a large battery for energy storage and, of course, a PV array for energy generation.
Battery
Most modern solar cars, like modern electric cars, use Lithium-ion batteries for their main energy storage. This type of battery chemistry provides the greatest energy-to-mass ratio, which is also why they're found everywhere in consumer electronics like phones and laptops. The smallest unit in a battery is known as a cell, and a battery is (strictly speaking) an arrangement of multiple cells to provide a greater total capacity and/or voltage. An extremely common Li-ion cell size is known as the 18650, which is economic to purchase due to their popularity.
Cells that can be recharged are known as secondary cells, whereas cells that cannot be recharged are known as primary cells (AA alkaline cells).
The most important point to understand about rechargeable batteries is that they do not store electricity. Batteries store energy in the form of chemical energy, and it is chemical reactions occurring within the battery that either produce or consume electrons, giving the appearance of charge being stored and released. Thus, batteries cannot be thought of as a water balloon that is only at risk of being damaged and rupturing if too much "water" is put in them. Furthermore, it is not valid to assume that batteries are fully "depleted" when they reach 0V. Voltage is not equivalent to remaining capacity!
In reality, because batteries only contain chemical reactions, causing the voltage between the terminals to go above or below its operating limits, regardless of the current state of charge, will cause damage to the battery and potentially fire or explosions. Batteries also have a temperature operating range and leaving this range will also result in damage to the cell and dangerous results. These voltage and temperature operating regions are especially important when using Li-ion cells because they have both a very narrow safe region and a very high energy density.
Virtually all Li-ion batteries are monitored in real-time by a battery protection system (BPS). The BPS is usually its own PCB and is an embedded system located typically inside the battery enclosure. It monitors parameters such as cell voltage and temperature, taking appropriate action such as quickly disconnecting the battery from the car in the event that the battery leaves its safe operating region.
Motors
Solar cars use electric motors, usually mounted directly to the wheels, to move the car. Motors are large, heavy electrical devices that contain conductor coils and permanent magnets. In order to generate force, current must be passed through different coils at a time, which is the job of a motor controller. The motor controller acts as an interface to the motor by taking high voltage power and control signals from a digital control port and applying the appropriate current to the motor to make it move properly.
Steering
The typical design of a solar car's steering system uses a mechanism called a rack and pinion to transfer the rotational motion of the steering wheel into linear motion to pivot the front wheels. The steering rack is mounted between the front wheels and attaches to both using tie rods. When the pinion is shifted left of right, the tie rods push the front wheels to rotate them accordingly.
The steering wheel is attached to a long rod called a steering column, which mounts to the rack to couple it to the steering wheel.
Suspension
For simplicity, and because solar cars don't need to transfer the motion of a gas engine to the wheels, most solar cars do not have axles. Each wheel is mounted directly to the vehicle. Each wheel mounts to its suspension system which then mounts to the frame. There are many different types of suspension systems, each with different geometries.
PV Array
The photovoltaic array, arguably the most characteristic component of a solar car, converts solar energy to electricity both while the car is driving and when it is parked. PV arrays absorb a wide spectrum of light, with a large part coming from infrared frequencies. This means arrays will usually not work behind windows as many windows have films that reject most IR light.
Under full illumination, a solar car's array is designed to generate voltages exceeding 100V and thus is a safety hazard. Solar arrays should be treated in the same way as battery packs or wall outlets. Arrays are also extremely fragile and can scratch or crack when touched on their surface.
Electronic Control Units
The term "Electronic Control Unit" (ECU) is used in automotive engineering to refer to electronic embedded systems within a car that control everything from driver controls to ABS braking and power door locks. They are commonly connected together on a shared digital interface known as a Controller Area Network (CAN). This interface can deliver both data between boards and supply moderate amounts of low voltage power. The primary source of low voltage power comes from DC power supplies in the car that convert battery voltage (typically 120V) to 12V.
Midnight Sun's ECUs
Midnight Sun's current electrical systems uses 4 main ECUs to control the primary vehicle systems:
Power management: Controls power switches connecting high voltage system components like the battery, motor controller, and array. It performs the vehicle start up and power down sequences.
Battery protection (BPS): Monitors the main battery pack and signals a BPS fault in the event of cell over-voltage, under-voltage, over-temperature, under-temperature, and over-current conditions.
Driver controls: Contains driver interface with buttons and switches for toggling vehicle power, turn signals, horn, etc.
Lights: Routes and controls power to the vehicle headlights, braking lights, and turn signals, by receiving commands from the driver controls board.
Our electrical system also has a non-critical ECU for telemetry, which is equipped with a radio transmitter to broadcast vehicle diagnostic information to a team member in a chase vehicle during a race.
All ECU boards are designed and manufactured by the electrical team, which also contains a large software group dedicated to writing the embedded firmware for all ECUs.