From the results of the Pugh Chart, we decided to use the design with L-Shaped brackets for our final design, while keeping the pancake design as a backup. We chose the L-Shaped bracket design for several reasons: it scored the highest in the Pugh Chart, it scored well in several categories we deemed the most important, and it also didn't score extremely badly in any categories.
To move forward with our design, we needed to identify the most critical module and solve for the forces and stresses on the chair to figure out what materials we needed to make sure it wouldn't break
Most Critical Module: The L-Bracket
The most important part of our design were the L-Brackets since they are what enables the chair to fold. We need to solve for the forces on the L-Brackets to find out what type of material to use and also solve for the angles in the L-Brackets to optimize folded size.
W = 8 in
D= 17 in
L = 10 in
α = 30°
d = 7.2 in
*dimensions based off of existing wheelchairs
We wanted the folded size (w in picture at right) to come out to approximately 3.5 inches, a folded size similar to the Roughrider wheelchair. We set the minimum height d because we wanted the wheelchairs to be able to clear obstacles such as rocks and to still be able to do wheelies. Solving for the folded width, we got:
β = 25.4°
l = 8.87 in
Forces in the Frame:
Because the system is overconstrained, solving for the reaction forces in the frame was the hardest part of our project. We have 6 pages of calculations which you can download and look at here.
You can also look at our presentation that includes calculating these forces here.
The final design is pictured above. The L-Brackets are almost X-shaped, but the small bends relieve stress and allow the castor wheel to touch the ground without pitching the wheelchair forward. The side wheels are attached from a rod extending from the back, which allows the wheelchair to still fold. Not pictured is a armrest bar that extends from the bottom front of the L-Brace to the backrest of the chair to restrain the back from collapsing inward. To see close up views of specific parts, take a look at our prototype!
Questions? Contact us