Mechatronic design of a quadrotor test rig for system identification
This research study presents the design, development and construction of a mechatronic test stand for the evaluation of powerplant parameters on a quadrotor. As opposed to alternate forms of UAV, the power plant serves a dual purpose of control and propulsion emphasising the importance of the identification process. Since control and propulsion are coupled, the power plant (motor coupled with propeller) was studied in detail using a black box structure (establishing relationships between the inputs and outputs). Extractions of motor parameters in previous studies used traditional Brushless Direct Current Motor (BLDC) equations and propeller theory, however the accuracy achievable and confidence in the extracted parameters remained questionable. The constructed apparatus set and data acquisition process developed for this project served to satisfy this need by allowing for the extraction of the unknown parameters instilling confidence in the modeling process. An in-depth analysis of the thrust stand from conception to construction was performed with an ideal parameter selection for optimum data resolution during collection. Additionally four RPM sensors were constructed each relying on an alternate means of sensing. The sensors when benchmarked against one another showed a variation of less than 1% in RPM. In order to optimise the powerplant selection, 36 sets of data had been acquired consisting of 6 motors with 6 propeller combinations. A data acquisition Graphical User Interface (GUI) was created in Labview utilising the National Instruments(NI) programming structure establishing communication between the powerplant and sensors. Post processing of the data involved the development of an algorithm that isolated each steady state plateau, establishing the average value in that vicinity using a pre-defined user confidence offset. The algorithm, due to the target pattern implementation, performed as designed on all data sets except those that exhibited corrupt data patterns brought on by resonance. The algorithm establishes relationships between thrust, torque, RPM and the pulse width modulated input signal. The established relationships are then used as inputs into a developed six degree of freedom mathematical model. A mission profile was constructed with distinct phases of which the mathematical model was used to simulate. Each phase in the mission profile excited different modes of the quadrotor dynamics creating an ideal simulation environment in which changes can be implemented and studied.