The study took place at the Stanmore Clinical Research Facility (SCRF) at the Royal National Orthopaedic Hospital (RNOH), Stanmore. All participants gave informed consent to participate in the study. (Refer to Appendix __ ).
The generation of forces were gathered through the front castors of the wheelchair and through the push rim. The forces generated are then recorded and analysed to investigate the hypothesis stated. The wheelchair users P:C Ratio was then calculated to establish whether the users exceeded their capacity when performing such tasks and whether Rear Axle Position (RAP) was found to influence this.
As there are no existing methods for testing dynamic wheelchair stability of a manual wheelchair, an instrument was developed. Consequently, a force sensitive castor was designed to look at this pattern in more detail.
The chosen model was a 17" Quickie GPV, rigid frame lightweight wheelchair. The model was chosen as the most adaptable size for most test participants and was then configured to suit each individual’s needs. The wheelchair weighs 18kg with nearly 7kg of added weight due to an attached equipment. The wheelchair is fitted with 25" solid tyres to accommodate the Smart Wheel technology and 5" solid castors. There is a 3-degree camber on the rear wheels.
Figure 1. Quickie GPV Wheelchair
Each participant was set up in the Laboratory’s test wheelchair.
Only one wheelchair could be used as the instrumentation was not interchangeable between wheelchairs.
1.3.3 Development of the Castor Force Transducer
An earlier work at ACDS (spell out acronym) (WOWSUP, 2005) using a wheelchair Ergometer showed that there was a substantial weight shift between castors and rear wheels during the propulsion cycle, which subsequently increased with the pushing resistance. The Ergomenter used force plates beneath the front castors during propulsion. The study explored what happened to the Ergometer when users propelled their wheelchairs to perform functional activities. A force sensor was integrated into the castor stem of the wheelchair to examine weight shift during functional mobility. This was initially constructed in combination with the castor stem and a number of washers to accommodate its size.
Figure 2. The Wheelchair Ergometer
1.3.4 Calibration of the castor force transducer
This was completed by loading the wheelchair with known masses and recording the voltage output from both the force transducer in the castor and the force plate underneath it (force plates already calibrated for previous testing). This calibration produced 2 curves in order to demonstrate whether a linear relationship was achievable