Logo credit: Design. Build. Fly Business Subteam, Spring 2015
We used this test rig (below), designed and built by some of my teammates, to test our propulsion system. Each propulsion system consists of some combination of a brushless motor, a propeller, and a battery pack of nickel-metal hydride cells (NiMH) as per competition regulations. The test rig is a pair of perpendicular metal legs of equal length with a pivot at their connection point. When the motor attached to the vertical leg is run, the trust of the motor causes the system to pivot slightly and transfer an equivalent force to the balance under the horizontal leg.
We tested many different motor-propeller-battery pack combinations. All of the battery packs were made from scratch by soldering and gluing cells, wires, and connectors, as shown below. The pack below was called 22S2P, which stands for 22 cells connected in series that are then connected in parallel to another pack of the same size to increase the capacitance of the system while maintaining the same voltage. I was responsible for planning tests and held the primary responsibility for building battery packs.
We would then test the system to determine if it meets certain power draw, thrust, and battery life needs. Below is a video of me recording the wind speed generated by the system. The propeller is pushing the system away from me and I am standing further from the blades than it may appear! It was a very powerful system.
After testing, we would record our results (a total of 19 spreadsheet inputs per test!) in a large spreadsheet, into which we had built most of our calculations.
We then compared these data points to the simulated results in eCalc, an online calculator program for remote control airplanes that allowed us to input our customized propulsion systems. While there was generally a large margin of error between the eCalc results and our test results, it was helpful to identify battery issues and systems that may be unsafe to run.
Finally, we analyzed charts generated by our EagleTree sensors and software in order to characterize the battery behavior over the entire duration of a run. The chart below shows a series of runs with three different battery pack sizes and a discharge test (running the batteries for as long as possible).
During the spring, we began narrowing in on the most viable system for competition. Below are flight test videos (Credit: Design.Build.Fly project team, Spring 2015). They are a bit long, but the takeoffs and landings are pretty exciting! The plane lands at 2:15 in the first video and 2:00 in the second video.