Our Final Results (Group-Sonoma, Faith, Maya)

During the creation of our car, we used our physics knowledge to decide on it’s design and to fix the problems we eventually found. The first stage of this project was the designing. When we designed our car, we wanted it to be able to move forward, backward, and go fast. Based on these ideas, we had to make some design choices backed by our physics knowledge. One of these choices was our building material. We chose to use carboard because it is very light, and it wouldn’t slow our car down too much while providing good support. Another choice we made was the decision to attach our motor to the back wheels. We did this because we found that in theory, rear wheel drive (RWD) is faster than front wheel drive (FWD). When the car is accelerating, all the weight shifts to the back end driving wheels, which helps with traction. We also wanted to have a larger driven gear (40 teeth) and smaller driver gear (10 teeth) because, referring to our gear worksheet, we know that this combination of gears creates more torque. The more torque you have, the faster the vehicle goes. In our last speed design choice, we wanted to include a rear wing. The rear wing helps reduce the low pressure zone behind the car, which means less turbulence is created and drag force is reduced. This creates downforce so that the vehicle has more traction and stability at higher speeds. When we designed for our car’s directional mobility, we decided to use an H-Bridge circuit as we wanted it to go both backwards and forwards. An H-Bridge circuit works by getting the electrical current to flow in different directions, which in turn makes the motor spin in different directions. This would then allow our car to move backwards and forwards. The rest of our design choices didn’t involve as much physics knowledge, as they were basically just visual appeal.

All these design choices were great in theory. As we built our car into reality, though, we found many problems that arose with our original design. The biggest problem was that our car would not move. The circuit worked well, but our motor was having trouble turning the driven gear. We realized that the mass of the car was too much for our motor to push, and it was not able to do the amount of work needed to accelerate our car.  In an attempt to ease the stress on our motor, we kept the carboard material, gear ratio, and the rear wing, but most of our car changed as well as the wheels. Originally we were using four Makerspace wheels, which were too chunky and heavy for our little motor. Instead, we removed one of the front wheels, and changed the material of the remaining three wheels to 3D print plastic. We also got rid of the tread on the wheels, allowing, them to roll easier. This lessened the amount of work the motor had to do by reducing the mass and friction. In addition to getting rid of one of the wheels, we got rid of any extra cardboard weight. In the end, our car was the fastest out of three classes with a time of 7.90s. By using our physics knowledge, our car went from non-mobile to a real Lightning McQueen!