A telemetry-based velocometer to measure wheelchair velocity

The purpose of this paper is to present a telemetry-based velocometer that has the ability to measure wheelchair velocity. Five studies are described which provide measurements of the validity, dynamic response, reliability and resistance of the velocometer. Validity: a linear relationship was found when velocity calculated from the velocometer was plotted against three test velocities. The average root mean square deviation (ARMSD) was used to compare velocity calculated from the velocometer with velocity calculated by manual digitising at 200 Hz. The ARMSD calculated for each test speed from three trials were 0.06±0.01, 0.27±0.05 and 0.48±0.16 ms−1 at 1, 5 and 9 ms−1, respectively. Dynamic response: expressed as a percentage of the average mean trial velocity, the ARMSD for the five acceleration and five deceleration trials were 6.5±1.8% and 6.9±1.2%, respectively. Reliability was assessed from a comparison between mean trial velocity calculated from velocometer output and the speed of the motor used to spin the wheels. Expressed as a percentage of the mean trial velocity, the mean±SD of the differences were 0.00±0.17%, for the ten disc wheel trials and 0.00±0.41%, for the ten spoke wheel trials. Velocometer resistance calculated as a factor of the mechanical resistance of the wheelchair rear wheel spinning in air were −0.50 and −0.91 N, for the disc and spoke wheel, respectively. Velocometer resistance calculated as a factor of the total mechanical resistance of the wheelchair–wheelchair user system were −1.37 and −1.82 N, for the disc and spoke wheel, respectively.