RollynRoyce

Rollyn Royce

A mobility assistance device intended as an attachment for present wheelchair users that addresses current propulsion modes and reducing repetitive stress injuries on the hand.

Senior Design Capstone
ASU || 16'-17'
Concepts - Product Design, Testing & Analysis, Manufacturing

Current handrim driven wheelchairs have been found to be an inefficient mode of transportation, and these methods are often strenuous for users. To address these issues, the capstone team looked at creating a lever and gear mechanism that is attached to the wheel itself. This wheel along with the propulsion system suite are the final product that was designed.

In terms of ergonomics, the hand rim type wheelchair has been recognized as a very strenuous method of locomotion. Net mechanical efficiency seldom exceeds 13%, whereas gross efficiency rarely exceeds 11%
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Even though electrical wheelchairs proves a growing industry, the vast population of wheelchair users, roughly 1.5 million, use manual wheelchairs.

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The mechanical advantage of levers give signicant improvement for making the wheelchairs lightweight, less expensive and integrating easily replaceable with common bicycle parts
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Report Presentation Poster

Product Design Process

OUR TARGET AUDIENCE - Our first task was seeking out the real stories of actual wheelchair users. We used social media platforms like Reddit to gain some insight to real issues plaguing this demographic worldwide. We then focused on collecting feedback from individuals in our community and in our school. And lastly, we canvased wheelchair repair shops to identify common shortcomings of traditional wheelchairs.
CONSTRAINTS & REQUIREMENTS - Based on the feedback we had collected, we believed that propulsion efficiency, the relative ease to propel one's wheelchair, would be our direction. Along with our direction, we had the following requirements: A) New designs shouldn't impair the user from fitting in doors, or carrying the wheelchair in a vehicle. B) New design should allow the whole wheelchair to be under 30kg. C) New design should allow the user to use product for at least 2 years. D) The complexity was to be minimized, so that the user can fix any issues themselves. E) Lastly the design should follow Americans with Disabilities Act Title III Regulations, part 36 and ISO 7176
DEVELOPING UNIQUE CONCEPTS - Ideas were collected by listing key design principles that were believed to be critical to the function of a tailored wheelchair.

My role as Chief Engineer was to lead the
Hardware Testing Activities and CNC Machining

Proof-of-Concept Testing:
Choosing Lever Position to Calories Burned

This test will look to understand the effect of a lever at different lengths. From previous hand calculations, it was seen that the lever length has the effect of increasing the torque felt on the system and thus increasing the overall efficiency. By using the this test we will see if a lever system at ‘high’ versus a ‘low’ grip will provide insight to the efficiency of the system. An elliptical can be modeled as a lever actuated system.

The levers on an elliptical allow the reciprocating motion to be conducted as the user pulls and pushes on the lever. The approach here will look at finding how much work a user puts into a lever at different lever lengths, and finds the effect of the total wattage produced by the system. Using different lengths, one can find the wattage produced by the system, to the calories a user burns due to his/her heart rate and METS number. Overall the testing shows a positive correlation between lever length and the propulsion felt on the system. Using an analysis of variance method, we found that the data due to using a lever was statistically different, having a P value at 0.18 %, which effectively rejects the null hypothesis. Overall from this test, we believed that using a lever caused the person to exert less energy as they produced power.

Propulsion Efficiency: Efficiency of Calories burned to Watts Produced

Propulsion efficiency is defined as the ratio of the power being put into the system and the power outputted. For the purpose of this test, we had assumed the power out of the wheel could be best modeled as the power of a rotating body. Thus by knowing the moment of Inertia, the angular acceleration and the rotational speed, we could theoretically calculate the power outputted by a rotating wheel.

The power inputted was very difficult to model. Ideally the use of a metabolic cart would have proven sufficient. However, since this was not feasible given our short testing time frame, it was agreed upon instead to use the a model that correlates heart beat and the MET number to find human energy expenditure. Using the info from the grand mean and a 95% confidence interval, one can assume that the efficiency of the traditional system is roughly 3.0 %. We understood that these results wern't definitive, and could be modeled better with better measurement systems.

Regular Wheel Chair Efficiency

Variance of Regular Runs

General Usability Testing

Checking compliancy with Americans with Disabilities Act Title III Regulations and Wheelchair Standards

Challenges in Manufacturing

One of the major challenges for this project was proper foresight to design. This stemmed from many OEM parts never having fully spec’d documentation. To overcome these challenges, we relied on our design and manufacturing adding leeway for more tolerances and capability for modification later on during the assembly phase. A component which exemplies this issue, and thus caused a lot of rework, was the coupler. The coupler component was a unique design specificly required to transfer motion from the lever to the hub. It had to be designed to fit over the splines of the hub where a cog would normally sit. The coupler was made out of 6061-T6 aluminum and machined using a CNC Mill and finished on a lathe.

Project Conclsuisions: There were a number of setbacks and compromises made along the way that hindered the performance of this product, which ultimately lead to not meeting our requirements. For one the testing could use significant upgrades. The propulsion efficiency testing needed more user feedback and better equipment to adequately track the efficiency of the new system vs. the old system. Another cause for concern was the product’s lack of stability on inclines. If we could have performed the test comparing two of the same wheelchairs, one with and one without our system, we could have gained better insight. Another method to increase the stability of the prototype on inclines would be to lower the center of mass by choosing lighter lever material. Because of the compromises made this product still needs further development prior to market.

Recomendations :
One of the biggest setbacks for this product was relying on existing bicycle components and adapting them to a wheelchair. If sponsored, this design could be minimized to a hub and lever. The multiple gears, disengagement, and freewheel features could all be integrated into a single hub rather than relying on a component for each feature. Overall budget was one of the limiting factors for this project.

Furthermore, adequate human trials with this product would take at least a year, especially getting the test subjects needed with the use of metabolic cart. Testing could have been expanded further to incorporate more human-centered design methods. Finding what lengths would be better for the lever, what travel distance produced the cleanest transfer of energy, and how to have a more stable design. We believed with these improvements, the gross efficiency of the design could be vastly modified. Ultimately, we seek to increase the mobility of those with disabilities and are a highly motivated team with the skills and knowledge to accomplish that goal.