Purpose
Group C elected to focus upon developing the most efficient, powerful, and accurate method of propulsion throughout the course of Advance Research and Development for the project. This was chosen as the AR&D focus as the group believed it was the best way to develop most efficient and reliable AEV possible while minimizing the costs of production and performance. An AEV that meets these requirements could be presented by Watts Scientific as a proposal for the Smart City Columbus initiative to advance the field of public transportation.
Methodology
This Resulted in a total of four design iterations being tested, each contributing to the progression of the final design. Each of the designs were tested by running three trials with code designed to execute the task of accelerating the motors to 25% power over 3 seconds then traveling to an absolute position of 5 feet before cutting power on the flat rail. Following each trial, data was extracted from the AEV on its energy usage over time.
Designs
Design 1 consists of the basic components of the AEV kit with the propellers separated and facing the same direction on the T-shaped base. This is the Side-by-Side Configuration and served as the relative sample/control design.
Design 1: Side-by-Side Propellers
Design 2 consists of the same components except the addition of a custom dual motor bracket to hold the motors and propellers coaxial, or in line, and facing the same direction. This is the Coaxial Configuration.
Design 2: Coaxial Propellers
Design 3 is the same as Design 2, except the propellers face each other and rotate in opposition to each other. This is the Contra-rotating Configuration. This design was created as theoretically, contra-rotating propellers more efficiently and powerfully generate thrust in the same direction due to increased airflow and a balanced net torque.
Design 3: Contra-Rotating Propellers
Design 4 is a completely different design from these propeller configurations. The design consists of a single motor held to the arm by a custom single motor bracket, all fastened to a rectangle base. The motor is connected to a custom pulley wheel with a central divider such that a rubber band can belt the pulley on either side and belt the wheels. This is the Crossed Belt Direct Drive design. This design was created with idea that the efficiency losses of propellers could be negated by directly applying force to the track.
Design 4- Crossed Belt Direct Drive
Results
Of the three propeller based designs tested it was found that the side-by-side propellers configuration was the most efficient, using approximately 28-32J of energy compared to 38-43J of energy per trial consumed by the coaxial design. There was some error in this experimentation as the dual motor bracket was not included in the first design tested, but this did illuminate how much of a factor additional weight plays in energy consumption. The contra-rotating propellers did not move the AEV on the track once the motors started, and due to this design failure data was not extracted from the run. This failure is most likely due to a missing element of the complex design.
As the Side-by-Side configuration proved most efficient, it was selected as the design to be used for Performance Tests 1 and 2. After these Performance Tests were completed, focus was shifted to developing the direct drive design. Executing the same code
Executing the same code as the propeller configurations, the direct drive design consumed significantly less energy than the side-by-side propellers configuration as evidenced by the graph of their respective three trial averages above. The direct drive consumed 18J of energy on average, approximately a 40% reduction from the 30J consumed on average for the sample configuration. The direct drive was also faster, as evidenced by the earlier onset energy plateau in the graph which signals when the power was cut off upon reaching the desired absolute distance. Less swaying was also observed for the design during these runs.
Conclusions and Recommendations
Although the sample AEV proved to be the most efficient of the propeller based designs, it could not compete with direct drive. The latter achieves a simplistic, lightweight design with the use of a single motor. The inclusion of the rubber band increases the traction of the AEV, providing for greater acceleration and stability in mobility and braking. As the Crossed Belt Direct Drive Design used less energy, completed tasks faster, and appeared more stable on the track, it is the final design to be used for the Final Performance test.