Hand-Operated Riding Lawnmower for Paraplegic

Designed by: Wan-Yin Chan, Megan Lan, T.J. PayneAdvisor: R. Steven Couch, M.D.

Professor: Paul H. King, Ph.D., P.E.Vanderbilt University, BME 273

http://vubme.vuse.vanderbilt.edu/group14_99

Project Goals

• Problem: Subject with T8 spinal cord injury is unable to safely operate riding lawnmower due to lack of lower body control

• Objective: Modify a riding lawnmower to address the physical limitations of a paraplegic and to further enhance safety

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Procedure

• Consultations with subject• Breakdown of project into 3 phases• Detailed analysis of possible solutions• Consideration of safety and cost efficiency • Final selection of optimum modifications• Implementation of design and reinforcement

of materials• Testing and evaluation

Subject Information• Age: 27• Weight: 165 lbs.• Height: 5 ft 8 in• Shoe size: 10.5• Level of Education:

Associates Degree in Mechanical Engineering

• Level T8 Spinal Injury• Wheelchair Model:

Action Terminator with 25 inch wheels

• Lawn: flat, with a few obstacles (trees, garden, etc. - see picture below)

Phase I: Brake Conversion• Problem: Subject is unable to use foot brake safely

due to absence of leg control• Considerations:

– Standard foot-powered push pedal attached to pull cable • Activates brake and clutch for shifting gears

– A 2.5-inch pull of the cable is required to stop the mower • Possible Solutions:

– Bicycle-style handbrake attached to pre-existing cable– Push-lever system similar to that employed in subject’s car– Single fulcrum pull-lever system (Final Solution)

Brake Modifications

• Installation of pull lever system– Provides longer pull than handbrake– Mechanical advantage

• 1/3:2/3 total length ratio or 12”:24” cable-fulcrum: fulcrum-handle distance

– Fewer moving parts than push lever• Lower risk of mechanical failure

• Components– One 36” x 3/4” steel pipe– One 1/4” x 2” hex bolt with two 3/16” hex nuts and

lock washers

Schematic of Brake Conversion

Phase II: Mount/Dismount• Problem: Subject has difficulty transferring into the

lawnmower without overshooting since lawnmower seat is 8 inches higher than wheelchair seat.

• Possible Solutions: Swing-away handle bar, external overhead bar, ramp (Final Solution)

Vertical Transfer: 8 inches (Difficult)

Horizontal Transfer: 16 inches (Easy)

Ramp Construction• Approach:

– 1 in. rise to 1 ft. run ratio (building code requirements)– Ramp will increase wheelchair seat height by 7 inches to allow

subject to mount safely– Border around ramp edges prevents wheelchair from slipping– Make platform area large enough to maneuver wheelchair safely and

easily• Dimensions of Ramp: (wood obtained from Home Depot)

– Height of platform: 7 inches– Length of slope: 7 feet– Width of slope: 48 inches– Platform dimensions: 60 x 60 inches (wheelchair length = 28 inches)– Border around edges of ramp: 2 inches deep, 4 inches wide

Phase III-a: Foot Restraint

• Problem: Legs and feet tend to slip off footplate due to vibrations from engine

• Solution: Install velcro footstraps to hold feet in place

• Approach: – Used velcro material for easy size adjustment– Foot space dimension is based on max shoe width (4.5 inches)– Attached by adhesive to bottom of footplate for stability

• Dimensions:– 1 inch wide velcro straps (donated by Weldas Company)– 5.5 inch wide foot space

Phase III-b: Body Restraint• Problem: Subject may fall out of seat while

lawnmower is in motion due to lack of lower body control

• Solution: Install car seatbelt to contain subject in seat• Approach:

– Bolted seatbelt at middle back of seat – Secured seatbelt in place at both sides of seat

• Dimensions: – 2.5 inch wide used car seatbelt (donated by West Nashville Auto

Body Shop)– 3 inch steel fasteners

Safety and Literature Review• Safety Review: Subject is able to maintain full control

of vehicle by using converted hand brake while steering and shifting gears. Lower body is sufficiently restrained. Safety of mount and dismount process is facilitated by ramp.

• Literature Review: Current items on the market for handicapped vehicles are unacceptable for our purposes:– Not specifically tailored to the various riding lawnmower

types and controls– All available conversion options (mechanical and digital) are

expensive ($1000+). Total cost of our modifications: $100

Acknowledgments

• R. Steven Couch, M.D. Vanderbilt Stallworth Rehabilitation Hospital

• Mark Singer Easter Seals Tennessee

• Kenton Dickerson Center for Independent Living

• Paul H. King, Ph.D., P.E. Vanderbilt University BME Department

• Vincent Goussen and Sebastien Daleyden Designsafe gurus