One alternative propulsion technique that was proposed was that of a Sail, along with the propeller, to harness the wind around the AEV. This process unfortunately wasted the first testing day, but overall resulted in the team getting a deeper understanding of the propulsion.
Test code:
celerate(4,0,55,3); //Accelerates all motors from 0 to 55% power in 3 seconds
motorSpeed(4,45); //Sets all motors to 45% power
goFor(5); //Runs all motors at 45% power for 5 seconds
brake(4); //Brakes all motors
Day 1: The basis of testing on day 1 was supposed to be varying sail material and configurations.
Observations: It was observed that the AEV did not move at all even though the propellers were functioning normally. The same observation was recorded even after changing motor speed, sail material and sail height configurations. This unfortunately resulted in a loss of one whole lab day for the team.
Conclusion: After the first day’s testing, the team realized that there was a huge flaw in the data collected. During the previous test, the propellers were oriented the wrong way, thus resulting in them blowing air into sail. After detailed analysis of the forces acting on the sail and AEV, and a brief research online from Mythbusters (check resources), the flaw was detected.
The propeller and sail’s mechanism are opposite with respect to the air. While a propeller pushes air to move forward (opposite directions w.r.t each other), a sail moves due to wind (same directions w.r.t each other). Hence, when a propeller is used to blow into a sail, equal force is applied on the internal system but in opposite directions. This served as a perfect example of Newton’s Third Law of Motion.
To prevent this from happening, a slight modification was proposed. If the side edges of the sail were modified to bend inwards, some air would thrust back, thus making the propeller’s force greater than that of the sail.
However, this configuration proved to be not as efficient as expected. Hence, it was concluded that, though a propeller and sail individually serve as excellent sources for propulsion, Using the propeller to blow into the sail would not be efficient.
(Resources: Mythbusters – Blow your own sail small scale)
Day 2: To resolve the flaw, the code could be slightly modified by adding a reverse(); command. This would result in the propellers to blow away from the sail, instead of into them.
The basis of tests on Day 2 was material of the sail. Two types of sail were tested – Standard Letter paper and a relatively thicker Folder paper. Three tests were conducted using each material, with varying height w.r.t the base.
Observations:
Standard paper: Following are the Power vs. Time and Distance vs. Time graphs with decreasing heights.
It was observed that the configuration where the sails center was aligned with the base showed the most efficient travel in terms of distance.
Folder Paper: Even though there were no significant changes in the independent variables for this test, the power vs. time and distance vs. time graphs showed huge inconsistency. Hence the data overall was scrapped and regarded useless.
Conclusion: It was observed that the AEV didn’t show significant efficiency with the sail, implying that there was not much wind energy to harness. The drag produced by the sails could not be countered effectively, hence slowing down the AEV overall. Thus, the team decided that the Sail-Propeller design was not going to be used in the future.