Design and Application of High-Speed Data Acquisition Aboard a High-Power Rocket in an Undergraduate Experimental Engineering Course

摘要

Undergraduate students in the Experimental Engineering Course at Harvey Mudd College design and fly sensor and signal-conditioning packages on high-powered rockets (total impulse of between 100 Ns and 600 Ns.) The data from these flights are collected using data loggers; this paper will describe the various data loggers used over the history of the course, from commercial rocketry flight computers through our current custom-designed and -built data logger, and the impact on student learning and quality of experimental data. A main objective of the course is that students move through a sequence of choosing scientific goals for their mission; model the expected behavior of the flight; select, design, and build an appropriate sensor package to measure phenomena tied to the scientific mission of their flight; and compare expected behavior to their measured results from the flight. In designing our flight data logger, we explicitly made choices regarding the ranking of various aspects of student learning. In particular, we wanted students to focus on proper signal conditioning for data logger input (voltages and impedance), and choice of number of channels and sample rate. A commercial 6-channel, 200 SPS per channel data logger was used (out of necessity) in the early offerings of the course, the use of which caused the students to struggle inordinately with choices involving small number of channels and low sampling rate. This affected the students' ability to achieve their scientific goals, especially the ability to measure different types of data for comparison purposes. As the course developed and we progressed through our data logger design, we chose 16 channels and a much-higher composite sampling rate of 400 kSPS (ranging from 25 kSPS/channel for 16 channels, up to 200 kSPS/channel for 2 channels). This choice was informed by a typical mission to measure vehicle acceleration, velocity, position, orientation, and vibrational modes, which requires 12 to 15 channels, and a composite sampling rate greater than 320 kSPS. The custom data logger allows the students a better chance at acquiring good data to satisfy their mission goals. Rubrics were used to assess four years of student work objectives relating to students' use of data acquisition systems and demonstration of experimental and analytical skills. Students using the MuddLog16 scored higher on the safe and proper use of data acquisition systems, and acquired more and better experimental data, which allowed them to satisfy their scientific mission. We saw no major differences in students' skills in scaling input voltages as we used different data loggers; students generally satisfied this objective no matter which data logger was used. Student consideration of buffering inputs was improved when we moved to the MuddLog16. The increase in number of channels and the higher sampling rate had the not-surprising effect of improving the quality of the experimental data acquired; we saw improvements in the ability of the students to more-completely compare experimental results to analytical or simulated predictions, satisfying a major learning objective. The higher sampling rate of the MuddLog16 had the effect of allowing students to be less-attentive to the potential of aliasing; future versions of the course should examine means to ensure students acquire and understand aliased data.