E. Week 5 (Battery Testing and Motor Amount Testing)

Week 5 marked the beginning of the advanced R&D labs where in-depth research was conducted to examine various aspects of the AEV. The topics chosen to focus on were battery testing and energy analysis. Multiple test runs were conducted on the AEV in a controlled environment to determine the relationship between battery voltage and distance traveled, as well as voltage versus number of trial runs.

The following code was written to test how battery voltage is affected by trail runs. 2 trials took place with the same code.

Voltage Test Code

batteryTesting
//accelerate to 30% power over 4 seconds
celerate(4,0,30,4);
//set the motors to 30% state and run for 2 seconds
motorSpeed(4,30);
goFor(2);
//brake all motors, stop for two seconds, and reverse direction
brake(4);
goFor(2);
reverse(4);
accelerate to 30% power over 4 seconds
celerate(4,0,30,4);
set the motors to 30% state and run for 2 seconds
motorSpeed(4,30);
goFor(2);
//brake all motors
brake(4);

The change in voltage after two trials was minimal; only .03 volts were lost over 2 trials.  The small difference in voltage can be attributed towards the limited run time. The code was revised so the AEV ran for more time to gain data that could be examined better.

Voltage Test Code Version 2

batteryTesting
reverse(4);
celerate(4,0,35,3);
motorSpeed(4,35);
goFor(4);
reverse(4);
celerate(4,0,30,3);
motorSpeed(4,30);
goFor(4);
reverse(4);
celerate(4,0,35,3);
motorSpeed(4,35);
goFor(4);
reverse(4);
celerate(4,0,30,3);
motorSpeed(4,30);
goFor(4);
4brake(4);

Voltage Plots

 

 

 

 

 

 

*Note: The voltage is measured in counts, the units for EEPROM voltage*

The above plot shows the voltages being used at specific marks for each battery’s trial run. Each follows a similar pattern between breaks and starting the engines. Noticeable peaks in voltage usage can be seen when brakes and motor restarts occur. Diminished returns can be seen from command to command. For example, the first spikes in voltage are likely due to brake commands.

Comparing all four plots on one graph reveals that how a diminished value for voltage affects AEV performance. A lower voltage resulted in lesser distance traveled for the AEV, especially when it came to braking. A lack of voltage led to less power output, which in turn led to less distance traveled via coastal braking.  In addition, when the AEV traveled for four seconds in the fourth plot, it covered half as many marks as the first plot. It is therefore important to consider the optimal voltage settings for the AEV to be at. Too strong of voltage will result in brakes covering too large of distances and too much energy being used, yet too little will not provide the necessary power for the AEV to operate correctly.

Considerations must be taken as to how to set the power settings so voltage is not diminished as quickly, as well as how to optimize the distances coastal brakes and goFor commands must cover. Furthermore, the code will have to be written in such a way that brakes and motor reverses are carefully chosen. Too many function calls of such nature will diminish the battery settings for an AEV run. Therefore, the addition of a servo would be practical for the coding and performance of the AEV.

Voltage vs Trials

After each trial run, the difference in voltage from the beginning of the run to the end was measured. The vectors for the voltage decrease and distance traveled for each trial run were measured and plotted above. As expected, a linear decrease was observed in voltage for each trial. Although the change in voltage was small between each trial, the distance the AEV traveled decreased significantly. Therefore, small changes in voltage led to large changes in marks traveled by the AEV. IT is important to utilize a battery at full voltage, even if the difference is .02 volts. This demonstrates the unpredictability of AEV performance by examining voltage, showing that other parameters of the AEV must be investigated.

Motor Amount Code

reverse();
motorSpeed(4,25);
goFor(2);
motorSpeed(4,20);
goToAbsolutePosition(100);
reverse(4);
motorSpeed(4,30);
goFor(1.5);
brake(4);

Motor Amount Graphs

One Motor

Two Motors

When comparing the one motor power vs time and power vs distance graphs, it is clear that one motor is more energy efficient, because less power is outputted per unit distance. However, two motors clearly causes the AEV to go farther, but at the cost of more energy consumption. We can conclude from these graphs that one motor is the most cost effective and energy efficient route to take, given our current resources.