Lab 7

The premise for Lab 07 was to continue to work towards a viable solution to solve the given MCR using a monorail system to transport R2D2 units. The team must use an AEV (Advanced Energy Vehicle) that will operate under specific conditions to complete the objective. The purpose of Lab 07 was to program the AEV to run on a straight track, verify the AEV wheel count sensor, and calculate the propeller force and the friction force. This lab was of utmost importance in the design and operation of the AEV because it would give the team insight on the operational effectiveness of the wheel count sensor and the types of forces that were acting upon the AEV.

The team’s AEV traveled properly along the track, stopping before the barrier with seemingly no issues. The team recorded the starting and finishing points of the AEV in inches. By hand calculating the amount of marks the AEV traveled and comparing it to the uploaded data from the AEV arduino, the team noticed the AEV wheel count sensors were not working properly. In order to complete the task, the team had to have a Marks Error of 2 or less, but the team vehicle had a Marks Error of 9. In an attempt to lower the error, the team worked with instructors to inspect the AEV to ensure the wheels were functioning correctly and the reflective tape was in appropriate condition. No existing errors were found in the vehicle itself, so the team attempted to measure the Marks Error again, making sure to take accurate measurements along the track. The error remained the same, varying greatly from the class average. To resolve this error, the team created a custom marks-to-inches conversion specific to their AEV. They took the total distance travelled (228.86 inches) and divided it by the number of marks measured (475 marks) to get .4818 inches/mark.

In Figure 1, it was shown that the AEV covered distance faster from 0-4 seconds, and then decelerated after that point and covered distance less quickly for the remainder of the time. The team theorized that the AEV would accelerate when the motors were powered, and decelerate when the power to the motors was cut. This theory agrees with the data shown on the graph, as the motor power was cut at 4 seconds and that was where the first inflection point of the graph was.

Figure 1: Distance of AEV vs Time

The team theorized that the AEV would accelerate while the motors were running, and decelerate for the remainder of the run until it stopped. In Figure 2, it was shown that the AEV accelerated for the first 4 seconds and then decelerated for the remainder of the time until the AEV stopped completely.

Figure 2: Speed of AEV vs. Time

The team theorized that the friction force would be the greatest negative-acting force on the AEV. The propellor force was equal to the sum of the friction force and the net force. The friction force was 3.9 gm (gram-force) and the net force was 6.3 gm. Thus: Fp=Ff+Fn=3.9gm+6.3gm=10.2gm. It was calculated that the drag force was less than 1% of the other forces, so the team theorized that this force could be considered negligible and not included in force calculations. Given this theory, it was proved that the friction force was the only negative-acting force on the AEV. Since the friction force was almost 40% of the net force, the team theorized that reducing the friction force would be the best way to increase AEV efficiency. The propellor force was 10.2 gm, and the team theorized that this force was sufficient to power the AEV. The net force was the propellor force minus the friction force. The net force was the actual force that the AEV receives to propel it forwards. It can be concluded from these forces that the team should focus on reducing the friction force.