Inertial monitoring of style & accuracy at 10,000 feet

Abstract

The "style" aspect of the parachuting sports of "style and accuracy" involves a parachutist diving earthward to gain maximum speed, tucking into a crouch position and performing a sequence of whole body rotations. The scoring of the rotations depends on the overall speed of the performance and the technical purity of the rotations. Given the cost and the 3000 m (10,000 ft) altitude location of the style activities, a parachutist practicing style activities has little opportunity for feedback on their training jumps. This paper investigates the usefulness of inertial sensors in the recording, analysis and provision of timely feedback for style activities. Several different sensors were used to collect data at different times. Some trials were collected with triaxial accelerometers coupled with single axis rate-gyroscopes and others with combinations of triaxial accelerometers, gyroscopes and magnetic sensors. Initial analysis of accelerometer outputs clearly showed key parachuting events such as entering free-fall, arriving at terminal velocity and the parachute opening. Rotations in the horizontal plane and the sequence of rotations were very clear in the gyroscope signal but for rotations in the vertical plane, both accelerometers and gyroscopes contained significant noise. Using triaxial gyroscopes, the vertical rotation became more clearly defined. The existence of tangential and centrifugal acceleration due to the offset between the sensor position and the axis of rotation provided a method of detecting the sensor orientation relative to the axis of rotation as well as determining an estimate of the offset distance. The gyroscope outputs not only provided an easily interpreted record of the turn sequence but other information on the technique such as the performing of an off-axis back loop or the beginning of a back loop while still completing the preceding turn. Additional data is currently being collected with newer devices to develop algorithms to determine the angles of undershoot and overshoot on a turn or back loop and the angle of off-axis rotation.