Executive Summary
The purpose of this lab was to run further analysis of the AEV data which including the calculation of velocity, kinetic energy, propeller RPM, propeller advance ratio and propulsion efficiency. The first three terms are physical parameters measured and calculated from the data and the last two terms are AEV performance characteristics used to evaluate the AEV design.
Applying the skills learned last lab, the group was able to download the data from the AEV board and convert the EEProm Arduino data readouts to physical parameters. By using Buckingham Pi Theorem, the group was able to find propeller advance ratio and then calculate the propulsion efficiency with the provided sample efficiency curve.
From the analysis result, the group made a single plot of supplied power, velocity, kinetic energy, propeller efficiency vs. distance as shown in Figure 1.
Based on the code and the plot, the group decided to divide the progress into 7 phases as Table 1. And the plot with phases was shown as Figure 2.
When analyzing the plot, the group observed the velocity and the efficiency were vibrating around a constant value during the constant speed phase. This was because that the uneven gap between the sensors would give different mark feedback during the same time period even when the AEV was in a constant speed. The group decided to regard this period as constant and would find new function to calculate better velocity result.
Based on the acknowledgements above, the group found that the propulsion efficiency of the AEV was constant during the constant speed movement phase. However, the accelerating phase would change the efficiency and the brake phase would cause a decrease of the efficiency on the plot.
When calculating the propeller RPM from the current, the group found that the RPM will be a negative value if the current is zero or very small. This was caused by the deviation of the sample calculation function. After discussion with professor, the group decided to convert all the negative RPM values to zero. In order to avoid dividing by zero when calculating advance ratio, the group assumed the propeller advanced ratio as zero when RPM is zero by applying the conditional statement provided.
In phase 1, the group found the abnormal moving back of the AEV. During this period, both the current and the propeller RPM was zero. After discussion, the group figured out that this was initial movements when installing the AEV on the track. And this part of data can be disregarded.
From this experiment, the group was able to estimate the propulsion efficiency based on code and testing. Improving the efficiency is important in improving AEV performance and also a fundamental skill in the following wind tunnel lab. By applying the efficiency test in this lab, the group were able to choose better propeller installing method in the following lab. The group will work on further analyzing of the data and applying the knowledge to improve the AEV performance.
Appendix
- Copy of Arduino Code
reverse(4);
celerate(4,0,30,2);
motorSpeed(4,20);
goToRelativePosition(197);
brake(4);
goFor(1);
celerate(4,0,30,2);
motorSpeed(4,20);
goToAbsolutePosition(369);
reverse(4);
motorSpeed(4,30);
goFor(1.5);
- Plots and Table
Figure 1. The supplied power (w), velocity (m/s), kinetic energy (J), propeller
efficiency vs. distance(m) plot.
| Phase | Ardiuno Command | Time Range(s) | Distance travelled(m) | Total Energy(J) |
| 1 | reverse(4);
celerate(4,0,30,2); |
0-2.101 | 0.0248 | 6.3963 |
| 2 | motorSpeed (4,20);
goToMark (197); |
2.101-11.222 | 2.4428 | 46.4154
|
| 3 | brake (4);
goFor (1); |
11.222-12.422 | 2.9512 | 46.5463
|
| 4 | celerate (4,0,30,2) | 12.422-14.462 | 3.5216 | 53.2884
|
| 5 | motorSpeed (4,20);
goToPosition (369); |
14.462-17.462 | 4.6004 | 66.4658
|
| 6 | reverse (4); | 17.462-17.582 | 4.6624 | 67.4533
|
| 7 | motorSpeed (4,35);
goFor(1.5); |
17.582-19.022 | 4.9228
|
77.1990
|
Table 1. The phase table.
Figure 2. The plot with phases divided. (The edges see on Table
Individual Calculation
Meng Cheng
(Sample: Line 120&121)
| Time(ms) | Current(Count) | Voltage(Count) | Marks |
| 6662 | 45 | 522 | 65 |
| 6722 | 42 | 523 | 67 |
Mass: 0.2571 kg Reference Voltage: 2.46V Diameter: 3in = 0.0762 m
T121 = t/1000 = 6.722 s
I121 = I/1024*RV*(1amp/0.185V) = 0.5454 A
S= 0.00124*marks
S121 = 0.00124*67 = 0.08308 (m)
V121 = (S121-S120)/(t121-t120) = 0.4133 m/s
KE121 = ½*M*V121^2 = 0.5*0.2571kg*(0.4133m/s)^2 = 0.02196 (J)
RPM = -65.59*I121^2+1927.25*I121-84.58 = 947.3 r/s
Propeller Advanced Ratio:
J121 = v121/[(RPM/60)*Diameter] = 0.3435
J > 0, Supplied Power > 0 keep the result.
Propulsion Efficiency:
η121 = -454.37*J121^3+321.58*J121^2+22.603*J121 = 27
Wilson Tang
Sample Line: line 66
| Time (ms) | Distance (Marks) | AEV mass (kg) | Current |
| 3422 | 13 | .597339527 |
Distance: s = 0.0124 * Marks
S66= 0.0124 * 13 = .1612 meters
Velocity; v1 = (s – si-1) = (.1612 – .1488) = .103 m/s
(t – ti-1) (3.422 – 3.302)
t66 = 3422 ms = 3.422 s
t64 = 3302 ms = 3.302 s
Kinetic Energy: KE= .5 mv^2 = (.5)(.2571)(.103)^2 = .0014 joules
Propeller RPM: RPM3 inch = -64.59I^2 + 1927.25I – 84.58
= -64.59(.597339527)^2 + 1927.25(.597339527) – 84.58
= 1043.6 Revolutions per Minutes
Propeller Advance Ratio: J = v = .103 = .077714
(RPM/60) * D (1043.6/60) *.0762
D = 3 inches = .0762 meters
Propulsion Efficiency: