Designers: Anna Beck, Maggie Finch, AJ Ford, Brianna Vey
Supervising Professor: Larry Bohs
INTRODUCTION
Our client is a manual wheelchair user who wants to mow her own lawn. The goal of this project is to design a lightweight mower that could easily attach to her wheelchair. The design includes a plastic base with wheelchair attachments that allow the base to suspend above the ground in front of the client’s wheelchair without impeding the wheelchair’s motion. Two cordless electric grass shearers attach to the base, providing a 12” cutting width. A switch in the upper attachment allows the client to easily turn the shearers on and off.
SUMMARY OF IMPACT
The device as it stands provides an even cut only on very smooth surfaces, because the shearers move up and down as the wheelchair travels over uneven terrain. Future work may consider a flexible suspension with a front wheel or wheels to help keep the shearers at a consistent height. Such devices were not considered because of concerns that they would make the front of the wheelchair too heavy for the client to “wheelie” as she desired for tight turns in her yard.
TECHNICAL DESCRIPTION
The main components of the Wheelchair Lawn Mower (Figure 1) are the Shearers, the Base, the Shearer-Base Mount, the Support Arms, the Foot-Bar Hooks, and the L-Bracket Attachments. The commercial Shearers (Homelite, model UT44170) weigh 2.1 pounds and have a battery life of about 1 hour.
The Base is constructed from ½” thick high-density polyethylene (HDPE) The lateral length at the front is 19”, and the width from front to back in the center is 11”.
The Shearer-Base Mount attaches the Shearers to the Base. A ½” threaded zinc rod (not shown) passes through existing holes in each Shearer, and fastens into HDPE blocks, which attach to the base.
The Support Arms attach the base to the wheelchair near the seat. Constructed from 1” aluminum tubing, each Support Arm contains a solid aluminum rod press fit at the bottom end, which is threaded to provide a secure attachment to the base with a 3/8” bolt.
The device attaches to the footrest area of the wheelchair with two Foot Bar Hooks, 1” diameter single-ended conduit clamps secured to the rear of the base with 3/8” bolts. The user slides these hooks over the footrest bar.
To hold the Base up, the Support Arms connect to an L-bracket Attachment on each side of the wheelchair. Each L-bracket Attachment includes an eye bolt fastened to a 5’’ x 1’’ x 1/8’’ L-bracket, one end of which slides into a slot below the seat. These slots were attached for a previous project. The eye of the bolt provides an attachment location for Support Arm Hooks fastened to the upper ends of each Support Arm. To mount the device, the user slides in the L-bracket Attachments, puts the Foot Bar Hooks over the footrest bar, and then puts the Support Arm Hooks into the eye bolt ends.
The power switches for both Shearers are wired in parallel, and the wires extended to the top of the right Support Arm, where a single toggle switch allows easy on/off control. The replacement cost for this device is approximately $200.