An Introductory Electric Motors And Generators Experiment For A Sophomore Level Circuits Course

The design, implementation, and assessment of an introductory electric motors and generators experiment in sophomore-level electric circuits courses are described. Two separate courses were enhanced by the addition of a common motors experiment for both students in the electrical engineering program (e.g., as student preparation for an electric power class) and those in other engineering majors (e.g., as student preparation for mechanical engineering lab experiences). The experiential foundation in the motors lab was designed to solidify concepts on efficiency of energy conversion and on motor performance. Topics included modeling of electric motors, predicting motor performance, and experimentally obtaining relevant motor constants. The experiment used a simple sub-fractional horsepower (Fischertechnik #32293: ~1.5 Watt) electric motor together with a unique small-scale dynamometer. In the experiment, students were required to experimentally determine the rotational speed of a motor using an optoswitchbased tachometer to find the motor voltage constant, kE; to determine motor torque constant, kT; to explore the use of a dynamometer to measure the conversion of electrical energy into mechanical energy; and to investigate the use of a motor as a generator. Despite the low-cost equipment, experimental results proved to be reliable, accurate, and repeatable. For example, the motor kE – kT match was typically found to be within 5%. Student learning was assessed through questionnaires at the beginning and end of the laboratory period. The questionnaires addressed both student knowledge and student confidence levels. The assessment showed a significant overall increase of both student knowledge and confidence scores as well as significant incremental increases. The data also showed that each incremental increase could approximately be represented as a normal distribution. Detailed analysis of the assessment data revealed strengths in student preparation for the experiment as well as certain course topics, such as the operating principles of a dynamometer, which will require more in-depth coverage in subsequent offerings of the course.