Advanced R&D Test: Power Braking vs. Coasting
Introduction
At the end of the AEV’s running, the AEV is supposed to stop at the gate to allow passengers to get on and off. The purpose of the Power Braking vs. Coasting test is to explore a better way to stop the AEV while meeting the team’s development priorities, which are safety, energy efficiency, and cost efficiency.
Procedure
During the test, the AEV started at the same position for each run and followed the same accelerating and powering pattern. For the power braking runs, when the AEV was supposed to stop, both of the motors would reverse the polarities, keep running for several seconds, and then brake. For the coasting runs, when the AEV was supposed to stop, the motors would be shut off and then coast till fully stop. Both braking patterns have been tested on five runs. After each running, the EEPROM data was downloaded for future analysis.
Results
Below are the distance and power usage data collected after test running.
Table 1: Braking Distances for Power Braking and Coasting for Five Runs
| Power Braking Runs | Reverse Start Position (m) | Final Stop Position (m) | Braking Distance (m) | Coasting Runs | Braking Start Position (m) | Final Stop Position (m) | Braking Distance (m) | |
| First Run | 2.6251 | 4.4082 | 1.7831 | First Run | 2.5632 | 4.6806 | 2.1174 | |
| Second Run | 2.6003 | 4.272 | 1.6717 | Second Run | 2.5632 | 4.7796 | 2.2164 | |
| Third Run | 2.6003 | 4.3463 | 1.746 | Third Run | 2.5632 | 4.8416 | 2.2784 | |
| Fourth Run | 2.6003 | 4.2224 | 1.6221 | Fourth Run | 2.526 | 4.693 | 2.167 | |
| Fifth Run | 2.5632 | 4.1977 | 1.6345 | Fifth Run | 2.5632 | 4.5939 | 2.0307 |
Table 2: Power Usage for Power Braking and Coasting for Five Runs
|
Power Braking Runs |
Power Usage (J) | Coasting Runs | Power Usage (J) | |
| First Run | 59.5769 | First Run | 58.6692 | |
| Second Run | 58.9988 | Second Run | 56.6206 | |
| Third Run | 60.0062 | Third Run | 57.8320 | |
| Fourth Run | 60.1285 | Fourth Run | 56.0146 | |
| Fifth Run | 61.0119 | Fifth Run | 53.9808 | |
| Mean | 59.7955 | Mean | 56.6234 |
Figure 1: Power Braking: Power vs. Distance for First to Fourth Runs
Figure 2: Coasting: Power vs. Distance for First to Fourth Runs
Data Analysis
After performance data for each run on power braking as well as coasting were collected through the Data Analysis Tool, some calculation was used to get the means and standard deviations of the braking distances. For the braking distance of power braking test runs, the mean was 1.682 meters (which is 66.220 inches) and the standard deviation was 0.067 meters (2.638 inches). For the coasting test runs, the mean was 2.162 meters (85.118 inches) and the standard deviation was 0.095 meters (3.740 inches). In the power braking runs, the AEV had a smaller average braking distance and a smaller standard deviation compared to that in the coasting runs. This meant that in the power braking runs the stops of the AEV were more accurately managed, thus ensuring the safety of the passengers.
The mean of power usage in power braking runs was 59.7955 joules, and the mean of that in coasting runs was 56.6234 joules. Generally, the coasting program would cost less energy than that of the power braking program.
From these perspectives provided above, the pros of power braking are that it would take shorter braking distance, which means that the stop of the AEV can be more precisely controlled. In this way, the safety priority was followed. The cons would be that it costs more energy compared to coasting since there were extra reversed motor runnings before the braking of the motors. For coasting, the explicit pros are that it has less energy consumption. Also, the program is shorter and easier for maintenance. The cons are that it took longer to fully stop, thus making it harder to manage the stopping position. And the passengers’ safety is harmed in this way.
There could be some possible errors in the data collected. The Li-Po battery was kept using without recharging, so the energy provided to the AEV during later runs might have lower input power. And the weight distribution of the AEV was not evenly balanced, which was that the rear part would be heavier since the battery and the chips were placed at that part. This could have also affected the performance of the AEV.
Conclusion
The team’s development priority is safety. Based on the test results and data analysis provided, the team will move forward with the power braking method.