Year: 2012
Projects: Single-Arm Operable Wheelchair
Client: Washington State University x Whirlwind International Wheelchairs
Category: Design Engineering
My Role: For my senior engineering project at Washington State University, my team and I were assigned to engineer and build a working concept of a single-arm operated wheelchair in a semester's time. My primary tasks included optimizing the wheelchair frame and developing the propulsion system. Additional collaborators on the project included our WSU advisor Professor Pezeshki, Sponsor Gene from HP Printers engineering, and Whirlwind International Wheelchairs.
Project Brief
The project’s goal was to create the first prototype in an ongoing effort towards mass-producing a single-arm operated wheelchair. The first prototype was designed with many considerations in mind but will primarily use as a proof of concept in an ongoing investigation into the vast scope of the industry.
The Need
A wheelchair provides invaluable mobility to those who would otherwise be confined to a mostly stationary life. Whether the cause is from a birth defect or some sort of injury, these people are essentially immobilized. Some of these cases are caused by residual ordinance detonations in areas where high levels of conflicts have ravaged the lands. Many of the typical functions of a common wheelchair are inaccessible to a one-handed user. The problem arises from the fact that to fully control the wheelchair, simultaneous operations must be done that requires more than one limb.
User Attributes
Environments
One-handed operation required to withstand hostile environments outdoors and indoors.
Total Costs
Primarily for third-world countries in Southeast Asia, Africa, and Afghanistan. Must be inexpensive to manufacture.
Ergonomics
Due to limited limbs proper ergonomics, portability and weight, and upkeep highly incorporated.
Adult Users
User age range from young adults to adults, 18 years old and above.
Constraints
Engineering factors & design constraints were outlined with the project advisor and sponsor, medical practitioners interviewees, handicapped individuals, and professional engineers interviews and publishings.
Engineering Metrics
Max Force Input
Sustained Power Output
System Weight (No User)
Weight Capacity
Max Operating Slope
Braking Power
50-60 lbs
7 Days/Week (50-60 lbs)
≤ 60 lbs
≤ 250 lbs (total ≤ 350 lbs)
≤ 13%
Travel 10 mph stop within 10 ft
Wheelchair Frame Retrofitting
Through computer research and wheelchair user interviews, I eliminated all reclining, tilting, and bariatric wheelchair types and focused on standard, folding, and rigid frames according to our constraints. The Whirlwind Rough Rider wheelchair was used as our base for modifications since it is suitable for off-road use and extreme durability. Whirlwind graciously donated a Rough Rider wheelchair for our engineering research.
Propulsion System Development
The 3-member bar linkage concept was developed under the goal to utilize both forward and backward motion of the input arm, while still remaining relatively simple to attach. The user easily pushes and pulls on the lever to propel them forward because the crank link rotates fully around the axle of the drive wheel. To vary the lengths and positions of the members of the system, multiple holes were drilled in the members to change where the joints are fixed. This allows customization of the mechanism to different torque positions that may be needed in different cases encountered while driving the wheelchair.
To attach the lever – a mounting system hub mount was designed. A majority of the members and mount pieces were made of plain mild steel. Smoothed tooled bolts and bearings were used to connect the linkage and mount the lever on the mount shaft, respectively. The crank was attached using a hexagonal peg through the crank and the hub mount fixture on the wheel.
Final Prototype O1
All components were 3D modeled, analyzed, and rendered using Solidworks. The complete propulsion system and supportive components were manufactured in the WSU machine shop and assembled by all project members. Furthermore, mechanical analysis was performed around the campus in isolated areas for regulated field tests.
ENGINEERING STEERING ANALYSIS:
Steering Success
Steering Failures and Solutions
The active steering provides the wheelchair ability to maintain a straight path while allowing the user to change directions while actuating the push-pull lever.
Failure: During rigorous testing, we found that the cables used to link the steering handle and caster wheel would break loose even after secure tightening during installation.
Solution: use a higher quality cable so a higher clamping force can be applied to fasten the cable.
Failure: Overall the steering performance proved to be unreliable – the pulleys controlling the active cable steering are at an uneven 2-1 ratio.
Solution: Adjust the ratio to 1-1 which would limit the rotation of the caster to about 45 degrees from straight to either direction. Then adding a bracket on the lever to secure the cable housing to allow the tensioners to work better.
ENGINEERING LINKAGE PROPULSION ANALYSIS:
Propulsion Success
Propulsion Failures and Solutions
On leveled grounds, we never faced any torque deficiency problems during testing. The fact that this system was able to capture the push and pull motion was promising, but the problems encountered rendered improvements realized during user testing.
Failure: The torque profile of the lever use is the weakest link. If the user stopped at a dead point, there is no torque to easily start again.
Solution: This was solved by simply pushing the wheel manually via hand rim on the wheels.
Failure: The system hindered at uneven grades where constant torque is beneficial.
Solution: Increase the overall torque with the decreased lever so each stroke of the lever motion can be restored as rapidly as possible.
Failure: Although oscillation is the last issue of this concept to be worried about, when the user needs to actively steer the chair, their whole arm will need to be moving along with the lever’s motion as well.
Solution: New concept 2 of a ratcheting mechanism would prove to be a great addition to the original idea.
