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| Executive Summary |
| Down Hill Wheelchair Project |
| Project Sponsor: |
| Dr. Jeffrey Rosenbluth, M.D. |
| Project Advisor: |
| William Provancher, Ph.D. |
| Project Team: |
| Jason Croft |
| Duane Ferkovich |
| Jason Hatch |
| Mark Swenson |
| Tom Tilley |
| Department of Mechanical Engineering University of Utah 50 S Central Campus Dr Rm 2110 Salt Lake City, UT 84112 |
| Introduction |
| The purpose of this report is to provide information regarding the Down Hill Wheelchair project, sponsored by the University of Utah Rehabilitation Clinic and the University of Utah Mechanical Engineering Department. This document provides an executive summary of the proposed design for a downhill wheelchair that is adapted for riders with limited mobility and spinal cord injuries and paralysis up to the C6 vertebra (mid thorax). This report is organized to provide customer requirements and design aspects that are critical to the functionality of the wheelchair and design process, followed by the project team’s approach to addressing said specifications. |
Downhill off-road riding is becoming increasingly popular among riders with disabilities, creating a need for an advanced wheelchair design to accommodate their physical limitations. The goal of this project is to design and produce a downhill wheelchair that will provide riders with the ability to participate in competitive sporting events or general outdoor activities, despite limited manual dexterity and limited leg use or amputated legs. The target rider will have up to a C6 level injury which means they typically have limited dexterity, limited hand strength, little or no abdominal support, no leg use and limited use of their biceps. The model rider does have almost full use of their shoulders, but lacks use of all other major arm and leg muscle groups.
The ability to maneuver on various types of rough terrain is of paramount importance. The design will allow a rider with limited mobility that is interested in downhill off-road racing to participate in the sport directly. Several different types of off-road wheelchairs exist on the market today. However, most designs do not have all the necessary accommodations required to suit persons with limited mobility. This fault with current designs is due to that fact that they require tremendous manual dexterity to steer and brake. The current designs also require full upper body strength and mobility which includes complete trunk control. The design team’s advanced model will address these specific issues of usability. The product will be a safe recreational vehicle that provides high performance on varied terrain, such as paved roads or mountainous descents.
Design Subsystems
The primary focus of this project is to provide a comfortable steering and braking control interface accommodating any rider with up to a C6 level spinal injury. The project team will focus its efforts on design innovations and will research and purchase components with a focus on low cost and availability to the end user. The design team will create a brake system, a control system and rider interface, a chassis and suspension system, and a propulsion system as described below.
Brake System: The braking system will incorporate the use of controlled disk brakes. Disk brake systems are very reliable and require little maintenance while simultaneously supporting heavy loads in a multitude of environmental conditions. The system will have user friendly controls allowing riders with limited dexterity and hand strength to use the braking system. It will also minimize force required for brake activation. In addition, the commercially available brake system will be enabled to stop the vehicle via a remote controlled by a third party in the event of a fatigued rider.
Control System and Rider Interface: A comfortable control interface between the rider and the chassis is an integral part of this design project. The control interface will also be used by the rider to steer the wheelchair. The interface must be adaptable to accommodate a variety of riders that may be mid- to high-level amputees or be partially paralyzed. To accomplish this, it may be possible to adapt the design to accept the seating interface found on uni-ski designs.
The user interface will include a form fitting seat that will allow riders with or without legs to be securely anchored to the wheelchair. Based on empirical evidence and conversations with physical therapists at the University of Utah Rehabilitation Clinic, the ideal rider position is slightly reclined, because it provides stability and a sense of security to the rider. Once securely fitted into the seat, the rider will have easy access and control of the steering mechanisms which will enable them to maneuver the wheelchair appropriately.
Chassis and Suspension System: The design team will require a new chassis design that will be able to traverse rough downhill terrain without inflicting a hard, shocking load on the rider’s spine. This will be accomplished by fitting the chassis with a full suspension system. The goal of the team will be to adapt an existing full suspension that has a long travel response to reduce the chance of rider injury. The project team is exploring purchasing and using the Honda TRX450R ATV suspension for use on the design. This suspension system is very robust, is readily available at a fraction of the cost of similar systems and has a large aftermarket range of replacement parts.
Propulsion System: Because many riders are not capable of propelling a vehicle on flat or inclined ground, the design will incorporate a method of propulsion. The auxiliary propulsion will be controlled by the rider and a microcontroller unit (MCU). The addition of a MCU will enable innovations such as a speed governor and anti-lock brakes. It will also allow the user input to be based solely on position, reducing the amount of strength required to operate the vehicle. Wheels and tires will be researched and purchased, although modifications will be made to fit the wheels to a purchased hub.
Design Approach
This project has been broken up into three phases to ensure that all of the design aspects are met. These phases were developed to provide the team with an organized structure that they will use to complete the project. Each phase is designed to contribute to the subsequent phase and completion of the phase is required to move to the next phase.
Initially, the design team will focus their efforts towards establishing customer needs and translating those needs into design specifications. The design requirements will define the specific product features of each of the innovation focus areas. Next, design concepts will be explored as a group in order to select the design that best matches the design requirements.
During the second phase of the project, the design team will focus on the development of prototype parts that will culminate in a fully assembled prototype. The design of the chassis will be the first order of business for the design team. In conjunction with the chassis design, the rider interface will be tightly coupled with the chassis design development. The braking system will be designed around the rider control interface on the chassis. At the end of this phase, the prototype will be a rough design that addresses all of the customer needs.
The final phase of the project will focus on the design refinement of the rough prototype to increase performance, reliability, and styling. In addition, the design refinement will include an accentuated focus on the safety of the wheelchair rider. The wheelchair must be designed to prevent the rider from using the wheelchair in a dangerous manner. This preventative design will be accomplished by having multiple third party riders demonstrate how they would use the product under supervision of the design team. The design team will note any instances in which the test riders could be endangered. Then the design team will refine the overall design to enhance the safety of the wheelchair.
Conclusion
The project will culminate in a prototype downhill wheelchair that will traverse a rough downhill course. The team will design the wheelchair following the prescribed guidelines and will ensure that all of the customer needs are met by the chosen design concept. The final prototype will be a working design that could be refined into a production vehicle.
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Authored By; Jason Croft