Of the 1.5 million Americans who use manual wheel chairs, roughly 600,000 are working age adults [1]. Despite significant design improvements in the last few decades, commercially available wheelchairs still lack the ability to provide users safe and affordable off-road accessibility. Typical wheelchair users are unable to access mountain trails and other off-road paths without significant after-market alterations or enduring hazardous passages with frequent assistance from others. A manual off-road wheelchair would provide users the ability to travel in limited access areas with increased independence. The goal of this project was to design and prototype a wheelchair for off-road use.

Andrew Baigrie, Connor Henley, Jeff Lance & Miguel Tovar

DESIGN & PRODUCTION OF AN ALL-TERRAIN WHEELCHAIRSECTION INSTRUCTOR

Mr. Scott Miller

SPONSORSJohn Norton &Private Donors

Mechanical Engineering Endowment Fund

ABSTRACT

BENCHMARKINGThe wheel chair manufacturing industry has historically been dominated by large manufacturing firms. The firms have primarily focused the development of their “sport” chairs on increasing speed and maneuverability on hard surfaces. Currently, no marketplace offerings exist for a manual chair designed for extensive off-road usage. Wheelchair users must either use aftermarket alterations or powered chairs whose design and performance typically resemble small all-terrain vehicles. A manual off-road wheelchair would provide users the ability to travel in limited access areas with increased independence.

Currently, all commercially available manual wheelchairs still lack the ability to provide users safe and affordable off-road accessibility. The closest competitive product to an all-terrain design is the Quickie XTR. The XTR has limited suspension to reduce road harshness, but lacks the ability to traverse any type of rugged terrain and does not have recumbent seating for user comfort.

Fig.1 Quickie XTR Wheelchair [2]

REQUIREMENTS

REFERENCES

ACKNOWLEDGEMENTS

RECOMENDATIONSFINAL DESIGN

Our completed prototype fulfills the proposed customer requirements. The design and production processes both illuminated opportunities for improvement and areas of potential future work. Based on our experience, our design recommendations focus on the fifth wheel assembly and power transmission. The current fifth wheel assembly experiences significant free rotation of the back caster during use. The free rotation of the caster hinders tight maneuverability by changing the orientation of the tire when jarred on rugged terrain. Another design possibility for increased functionality is the addition of power transmission to the chair. The power transmission would allow users the option to either push or pull on the wheel handrails to move forward. The power transmission could be accomplished by using a toggle gearing mechanism that could be shifted while parked. The ability to pull would allow users a significant advantage while climbing hills and would help decrease user fatigue.

Areas for improvement in manufacturing were identified during production of the prototype. A wooden jig (see Fig. 8) was constructed to ensure the correct orientation of components during assembly and welding. Our jig was constructed with standard contractor equipment and had significant tolerances relative to component sizes. For future projects, we recommend the production of a high precision jig. The time invested in a jig has a significant payback during the manufacturing phase.

[1] Kaye, Stevens, et al. “Wheelchair Use in the United States.” Disabilities Statistics Center, University of California. May 2002. <http://dsc.ucsf.edu/publication.php?pub_id=1>

[2] Invacare, “Product Catalog,” September 14, 2005. www.invacare.com

ME Design and Manufacturing Machine Shop: Mr. Robert Coury & Mr. Marvin Cressey

ME 450 Instructional Team: Professor Albert J. Shih & Mr. Scott Miller

School of Art & Design Metal Studio: Mr. Chris Whaley

University of Michigan Hospitals, Biomedical Engineering: Mr. Patrick Lobbestael

ProCEED: Mr. Peter Adamczyk

Ms. Julie Harrison

Both competitive and lateral benchmarking and customer surveying were performed to determine the most significant attributes for a wheelchair design in our target market. From this research, we developed the following customer requirements.

Fig.2 Customer Attributes.

Fig.3 Final CAD model.

Fig.5 Overview of frame. All dimensions are in inches. Fig.6 Detailed drawing of frame. All dimensions are in inches.

PRODUCT VALIDATION

Fig.9 The fifth wheel design is shown overcoming an obstacle.

Fig.4 Final model.

Fig.7 Chair disassembles to fit in the back of a compact car.

ME 450 TEAM 9

Fig.8 Wooden jig used during manufacturing.