People with disabilities often struggle with mobility issues, so there is a strong desire for devices such as powerchairs, which can provide more freedom. Currently, wheelchair demand in the US is increasing due to an upsurge in the elderly population. Often electric powerchairs suitable for outdoor use are extremely expensive, cannot be used indoors, and are not covered by medical insurance. In this project, these problems are addressed through the design of a chair which is suitable for both rough outdoor terrain and indoor use. This project is based on a request for a powerchair which our client’s son, who has cerebral palsy, can use on family trips in outdoor environments including grass, gravel, and sand. A photo of a previous nonfunctional prototype was provided to the team as a reference, and a full redesign was performed to resolve the problems identified.
Before proceeding with the design, various sources were consulted to gain a thorough understanding of currently available technology and design methods. Many different adjustment methods and features were considered, including an adjustable frame, tracks, and a lifting system for curb mounting. The overall design selected is a welded sheet metal frame with wheels, and it was determined that the chair should have an adjustable wheelbase width to provide both outdoor stability and indoor maneuverability.
Key considerations for the design include battery life, motor torque, maximum load, seat size, door width, and cost. The final specifications are based on the needs of the client, Kevin Sample, as well as an analysis of the wider consumer market. The width adjustment design uses an axle above the driving wheels, which are connected to it by sliding sleeves. Automatic adjustment is accomplished using a linear actuator. The drive wheels are large and run at low pressure to surmount obstacles and damp vibrations. Differential steering combined with rear caster wheels gives the chair a small turning radius, and its length is comparable to that of standard manual wheelchairs. The seat can be easily removed to access the battery and control system or to load the chair into a vehicle. A joystick is used to control the speed and direction of the chair, while a separate momentary switch is used for the linear actuator.
Throughout the modeling process, stress analysis was performed using simulations in Inventor. Any necessary adjustments were made to ensure that none of the parts will fail, considering both failure theory and fatigue. Various grades of aluminum were selected for the majority of the manufactured parts, due to their corrosion resistance and light weight.
The device is currently in the prototype manufacturing stage. If it is later marketed, a curb mounting device may also be included; this was decided against mainly due to cost and time restrictions. Space has also been left for a carrying basket, which will likely be added to the first prototype. The initial goal is to produce a single chair for our client, although the design may later be submitted for Medicare and ADA approval.