Effects of wheels and tires on high-strength lightweight wheelchair propulsion cost using a robotic wheelchair tester.

PURPOSE: This study was designed to investigate the effect of wheel and tire selections on the propulsion characteristics of a high-strength lightweight manual wheelchair using robotic wheelchair propulsion. MATERIALS AND METHODS: Four configurations were compared with differing combinations of drive wheel tires and casters, with the baseline reflecting the manufacturer configuration of a solid mag drive wheel and 8"×1" caster. The robotic wheelchair tester propelled the chair using pre-generated straight and curvilinear manoeuvres using repeatable and reliable cyclic torque profiles. Additionally, energy loss of the components was measured using coast-down deceleration tests to approximate the system-level rolling resistance of each configuration. RESULTS: Results indicate a significant decrease in propulsion cost, increased distance travelled and increased manoeuvrability across all configurations, with upgraded casters and tires. CONCLUSIONS: These results indicated that with better casters and drive wheel tires, the performance of high strength lightweight wheelchairs can be improved and better meet the mobility needs of users.Implications for rehabilitationWheel and tire selection can have a demonstrable impact on the propulsion efficiency of manual wheelchairsCoast-down test protocols can be used as a simple and cost-effective means of assessing representative energy losses across various surfacesWheelchair configurations can be optimized with proper knowledge of the main energetic loss contributions and the environments and contexts of use.

Effects of Incremental Changes to Frame Mass on Manual Wheelchair Propulsion Cost.

The objective of this study was to assess the effects of small, incremental additions to wheelchair frame mass (0 kg, +2 kg, and +4 kg) on the mechanical propulsion characteristics in both straight and curvilinear maneuvers. A robotic propulsion system was used to propel a manual wheelchair over a smooth tiled surface following rectilinear ("Straight") and curvilinear ("Slalom") trajectories. Three unique loading conditions were tested. Propulsion costs and system rolling resistance estimations were empirically collected using the robotic wheelchair tester. Propulsion cost values were equivalent across all loading conditions over the Slalom trajectory. In the Straight trajectory, adding 2 kg on the axle had equivalent propulsion cost to the unloaded configuration. Adding 4 kg on axle was comparable, but not equivalent, to the unloaded configuration with small (≤4.1%) increases in propulsion cost. This study demonstrates that small (0-4 kg) changes to the frame mass have no meaningful impacts on the propulsion characteristics of the manual wheelchair system. Differences in propulsion cost and rolling resistance were detectable but contextually insignificant.

Effect of Wheels, Casters and Forks on Vibration Attenuation and Propulsion Cost of Manual Wheelchairs.

Manual wheelchair users are exposed to whole-body vibrations as a direct result of using their wheelchair. Wheels, tires, and caster forks have been developed to reduce or attenuate the vibration that transmits through the frame and reaches the user. Five of these components with energy-absorbing characteristics were compared to standard pneumatic drive wheels and casters. This study used a robotic wheelchair propulsion system to repeatedly drive an ultra-lightweight wheelchair over four common indoor and outdoor surfaces: linoleum tile, decorative brick, poured concrete sidewalk, and expanded aluminum grates. Data from the propulsion system and a seat-mounted accelerometer were used to evaluate the energetic efficiency and vibration exposure of each configuration. Equivalence test results identified meaningful differences in both propulsion cost and seat vibration. LoopWheels and SoftWheels both increased propulsion costs by 12-16% over the default configuration without reducing vibration at the seat. Frog Legs suspension caster forks increased vibration exposure by 16-97% across all four surfaces. Softroll casters reduced vibration by 11% over metal grates. Wide pneumatic 'mountain' tires showed no difference from the default configuration. All vibration measurements were within acceptable ranges compared to health guidance standards. Out of the component options, softroll casters show the most promising results for ease of efficiency and effectiveness at reducing vibrations through the wheelchair frame and seat cushion. These results suggest some components with built-in suspension systems are ineffective at reducing vibration exposure beyond standard components, and often introduce mechanical inefficiencies that the user would have to overcome with every propulsion stroke.

Estimating whole-body vibration limits of manual wheelchair mobility over common surfaces.

Whole-body vibration (WBV) experienced during manual wheelchair use was quantified across several types of terrain (tile, sidewalk, decorative bricks, expanded metal grates). Over-ground travel was controlled using a robotic propulsion system. Vibrations along the vertical axis were measured with a triaxial accelerometer mounted to the seat of the wheelchair. Root-mean-square acceleration values were compared to the health guidance exposure limits established by the European Council using the WBV calculator tool published by the Health and Safety Executive (HSE). Vibrations along the vertical axis were well below the exposure values associated with health risks. Even the most aggressive tactile surface (grates) tested in this study would require more than 14 h of daily travel to reach the "exposure action value," and more than 24 h would be required to reach the "exposure limit value". Considering the average cumulative duration of active self-propulsion among manual wheelchair users is around an hour or less, none of the tested conditions were deemed unsafe or damaging.

Measurement of rolling resistance and scrub torque of manual wheelchair drive wheels and casters.

The effort needed to maneuver a manual wheelchair is a function of the occupied wheelchair's inertia and energy loss. The primary source of energy loss is due to the resistance of the drive wheels and casters on the ground. Specifically, manual wheelchairs have two major sources of frictional energy loss: rolling resistance and scrub torque. The objective of this study was to develop and validate component-level test methods to evaluate the energy loss properties of drive wheels and casters on different surfaces and with different applied loads. Rolling resistance is measured using a weighted coast-down cart and scrub torque is calculated by measuring the force required to rotate a plate that is loaded onto the tire's surface. Each test method was iterated and then applied to a cohort of drive wheels and casters. Both test methods demonstrated acceptable repeatability and the ability to distinguish energy loss parameters between common wheelchair components. The results show that caster and drive wheel energy losses can vary significantly across surfaces and with increased load on the casters. However, the findings also illuminate complex relationships between rolling resistance and scrub torque performance that embody a tradeoff in performance as applied to mobility during everyday life.

Propulsion Cost Changes of Ultra-Lightweight Manual Wheelchairs After One Year of Simulated Use.

Manual wheelchairs are available with folding or rigid frames to meet the preferences and needs of individual users. Folding styles are commonly regarded as more portable and storable, whereas rigid frames are commonly regarded as more efficient for frequently daily use. To date, there are no studies directly comparing the performances of the frame types. Furthermore, while differences have been reported in the longevity of the frame types, no efforts have been made to relate this durability back to the real-world performance of the frames. This study investigated the propulsion efficiencies of four folding and two rigid ultra-lightweight frames equipped with identical drive tires and casters. A robotic wheelchair tester was used to measure the propulsion costs of each chair over two surfaces: concrete and carpet. A motorized carousel was used to drive the chairs 511 km around a circular track to simulate one year of use for each wheelchair. After simulated use, five of the six wheelchairs showed no decrease in propulsion effort, indicating that the frames were able to withstand the stresses of simulated use without a detrimental impact on performance. In the unused "new" condition, rigid chairs were found to have superior (>5%) performance over folding frames on concrete and carpet, and in the "worn" condition rigid chairs had superior performance over folding chairs on concrete but were comparable on the carpeted surface.

Modeling manual wheelchair propulsion cost during straight and curvilinear trajectories.

Minimizing the effort to propel a manual wheelchair is important to all users in order to optimize the efficiency of maneuvering throughout the day. Assessing the propulsion cost of wheelchairs as a mechanical system is a key aspect of understanding the influences of wheelchair design and configuration. The objective of this study was to model the relationships between inertial and energy-loss parameters to the mechanical propulsion cost across different wheelchair configurations during straight and curvilinear trajectories. Inertial parameters of an occupied wheelchair and energy loss parameters of drive wheels and casters were entered into regression models representing three different maneuvers. A wheelchair-propelling robot was used to measure propulsion cost. General linear models showed strong relationships (R2 > 0.84) between the system-level costs of propulsion and the selected predictor variables representing sources of energy loss and inertial influences. System energy loss parameters were significant predictors in all three maneuvers. Yaw inertia was also a significant predictor during zero-radius turns. The results indicate that simple energy loss measurements can predict system-level performance, and inertial influences are mostly overshadowed by the increased resistive losses caused by added mass, though weight distribution can mitigate some of this added cost.