The mechanical systems form the structural foundation of the solar car. While the methods and technologies used in the mechanical systems are well established in the automotive industry, the quest for a light, yet reliable vehicle leads to innovation in mechanical designs. The mechanical systems can be subdivided into several main categories: chassis, suspension, brakes, and steering.
The chassis encloses and protects the driver, as well as providing the fundamental structure connecting the other mechanical systems with the body, as well as providing a mounting location for electrical systems. The ultimate goal of the chassis structure is to protect the driver in an accident and to provide a strong and stable platform for other systems. There are currently two prevailing chassis structures in solar car racing to date: the tubular metal spaceframe and the carbon fiber composite monocoque chassis. Stanford has traditionally raced with a tub style composite monocoque chassis. Other teams have used aluminum and steel spaceframes with varying degrees of success, and some teams have tried to integrate composite materials into a spaceframe style chassis.
The suspension is another major mechanical subsystem. The goal of the suspension is to isolate the car from road surface defects and perturbations. Besides enhancing driver comfort, the suspension can potentially enhance the responsiveness or stability of the solar car. The majority of solar cars utilize a short-long arm style suspension, also known as double wishbone for the front wheels. The rear wheels often also employ the double wishbone style suspension for four wheeled solar cars, while three wheeled cars usually employ a derivative of the trailing arm style suspension. Most solar cars use suspension components machined from billet aluminum, although several solar cars, notably the 1996 World Solar Challenge victor, the Honda Dream, used carbon fiber composite and magnesium components. Shocks and springs are usually off-the-shelf components, with everything from motorcycle fork struts to mountain bike rear shocks used in this capacity. Stanford has traditionally utilized a double wishbone style suspension for its four wheeled vehicles, and a trailing arm rear wheel for three wheeled vehicles, with either mountain bike or motorcycle springs and shocks; these configurations are pretty much the norm in solar car racing.
The steering system is one of the few inputs that the driver has in controlling his or her car, and as a result it is important to take a hard look at this subsystem. The goal of the steering system is, of course, to allow the driver to precisely change the direction of the solar car. There are many different styles of steering present in solar car racing, from rack and pinion to push pull to bicycle fork style steering. Steering controls vary widely, from the conventional steering wheel to handles like those found in a tank. In designing the steering system, the driver’s control authority and comfort in using the controls is of paramount importance, as well as the system’s stability in dynamic situations. Stanford has used a rack and pinion type of steering system with a steering wheel as the driver interface in their previous vehicles; some teams employ a similar system, while others have successfully used a push pull steering system with tank style handles.
The final subsystem of the mechanical group is the braking system. The braking system needs to be capable of stopping the solar car in the shortest distance possible without compromising vehicle stability. Like conventional automobiles, solar cars usually employ disc brakes, though some cars have employed drum brakes. The motor in the car is also capable of regenerative braking, in which the motor becomes a generator, and the torque necessary to turn the motor slows the car down. The mechanical calipers and the regenerative braking system need to cooperate to prevent unbalancing the car during hard braking. The calipers and rotors of the braking system are usually off the shelf or custom manufactured components. Though the components are bought off the shelf, it is necessary to choose these components carefully so that the driver can stop the car in a safe manner. Many teams use motorcycle or go-kart style calipers; however, some teams have successfully utilized mountain bike disc brake systems; Stanford has utilized both mountain bike and go-kart calipers in past cars.
The mechanical systems are built off tried and true systems, but their importance cannot be overstated. Failures in the mechanical system at best result in delays during the race and headaches in the pit; at worst, they result in serious injuries to team members. The Stanford Solar Car Project always strives for the most reliable and most competitive mechanical systems.