University of Rochester
Our team has created a novel device to allow for adapted control of a recumbent tricycle by users with unilateral upper body weakness. A γ-prototype has been constructed and has been tested for safety and efficacy. This report outlines the motivation for our design, reasoning behind decisions, our accomplishments to date, and our plans moving forward.
Why Is This Important?
Our target demographic encompasses everyone with any form of unilateral upper body weakness. This can be a result of a variety of causes. Eighty percent of the 700,000 stroke survivors every year result in hemiparesis (www.ninds.nih.com). Additionally, there are 18,500 new upper limb amputations every year in the U.S. alone (Dillingham, 2002). This gives us a total of well over a half a million new cases of unilateral upper body weakness every year. In addition to the physical weaknesses, these physical limitations often result in a mindset that the individual can never return to their previous lifestyle. Adaptive equipment can enable these individuals to participate in the sport of cycling, creating an avenue to be physically and socially active, gain a greater sense of independence, and gain therapeutic benefits.
Individuals with functional use of only one arm often have limited ability to participate in many common activities, including the sport of cycling.
We have designed, built, and tested a detachable and adjustable recumbent tricycle control system, allowing users to steer, brake and shift gears easily, intuitively and effectively with the use of a single fully functional arm.
Summary of Methods
In order to achieve our statement of purpose, we first had to identify our customer more completely. Through background research and communication with end users, we created a customer scenario and two tables separating design needs and wants. We used these tables to pair each need and want with a metric that can be tested to determine success. We then created a house of quality (HOQ) to determine the relative importance of the various needs and wants. Based on the HOQ, we confirmed our intuition that the most important metrics were those associated with centralized one-handed operation, followed by all metrics associated with the ease of use and efficacy of the device. Once the relative importance of metrics were established, we brainstormed ways to achieve these metrics and created an initial design schematic as well as a sketch of the system level design. When the initial design had been determined, we purchased plumbing pipe and constructed an α-prototype to demonstrate proof of concept. After our α-prototype verified the validity of our design, parts and materials selections were made and we proceeded to construction of our β-prototype. The β-device was tested for adherence to Consumer Product Safety Commission (CPSC) bicycle guidelines. Once we confirmed that our device was safe, it was tested for efficacy by a diverse group of individuals. Using their feedback and our own observations, we made minor design changes and created the γ-prototype. This prototype adheres to all CPSC safety guidelines, and has received stellar feedback from peers and end-users alike. The following sections provide images, charts, and descriptions explaining the process I’ve outlined above.
Our device is intended for use by cycling programs catering to individuals with disability, and may also be marketed to individuals for at home use. Most users of our product will be individuals who have unilateral upper body weakness, as well as some secondary weakness necessitating the use of a recumbent tricycle. Users of our device are seeking a means to operate a recumbent cycle with one hand, and participate in a sport they previously could not. They may possess a wide array of physical abilities, but it is likely that individuals using our device will have some secondary weakness. Due to the fact that adaptive cycling programs service a variety of individuals with different needs but have limited cycles due to budgeting constraints, they need their cycles to have both one and two-handed functionality. This consideration prompted our design to include removable and adjustable capabilities, which take a few of minutes to execute. Additionally, to accommodate a variety of cycles, we insured that our device could be mounted to most cycles we have encountered.
Customer Needs And Wants
|One-hand operation||Number of hands needed for operation||1 hand|
|Centralized steering, braking & shifting||Maximum linear distance between all controls (steering, braking, and shifting) from central point||6" or less between controls, middle of brake lever no more than 3.5 inches from handlebar (GPSC.org)|
|Effective braking||Distance it takes to stop after applying brakes at a given velocity||Complete stop within 4.5 meters of break application for a 68.1 kg rider at 1.5 km/h (GPSC.org)|
|Effectdive and intuitive steering||Turning angle from midline, user survey 1-10*||60° on either side, ≥ 7|
|Effective shifting||Percent of shift failure||
|Steering easily operated||Force on control necessary to cause wheel to turn||Equal force (N) applied to steering mechanism to turn, compared to stadnard recumbant tricycle|
|Ease of braking||Magnitude of force required to apply breaks||Less than 44.5 N to cause break pads to contact braking surface (CPSC.org)|
|Detachable||Can it be converted?||Conversion in under 10 min|
|Ergonomic||User survey 1-10||≥7|
|Aesthetically appealing||User survey 1-10||≥7|
|Durable||Uses until failure||>1000 uses|
|Adjustable control height||User height range for whom the producdt can be adjusted||Product should be adjustable for user heights from 5' to 6'6"|
|No interference with pedaling||Frequency of interference||0 occurrences of interference|
|Ease of Mounting/Dismounting||Minimum distance from back of seat to nearest part of control system||24"|
|Ease of Transportation||Types of car that can transport, and maximum width of tricycle||Fit in SUVs, mini-vans, trucks
Fits through standard 32" doors
|Ease of installation, adjustment and removal||Maximum time to install, adjust or remove system||10 minutes|
|Universal for common cycles||Types of cycles that product can be used with||All cycles with horizontal bar on handlebars|
|User sense of safety||User Survey 1-10||≥7|
To create our alpha prototype we went to Lowe’s to search for possible materials for prototyping, and chose to use steel plumbing pipe, because it’s outer diameter is roughly equal to that of the existing handle bar. We constructed the alpha prototype and secured it to the existing bicycle using duct tape. After demonstrating that we could steer with the alpha prototype we began work on the β-prototype.
After proof of concept was established by the α-prototype, we began conversations about realistic manners to reproducibly construct our β-prototype. We decided to minimize the number of parts by bending the pipe in the proper orientation. We kept our design essentially the same, except for replacing the steel pipe with much lighter aluminum, attaching the steering system via perpendicular eye clamps, and creating the interchangeable gear system with a small bicycle part, and two hooks that we constructed ourselves. We also added padding to the handlebar for safety and aesthetic appeal. After testing the β-prototype, minor adjustments were made for manufacturability. The γ-prototype is described in detail in the results section.
We have designed, built, and tested a detachable and adjustable recumbent tricycle control system, allowing users to steer, brake and shift gears easily, intuitively and effectively with the use of a single fully functional arm. An inverted “V” shaped aluminum handlebar is clamped to the crossbar of the existing handlebars, on which a rubber grip is centrally placed for the user’s hand. By loosening the clamp, the position of the handlebar can be adjusted in two degrees of freedom to fit each user, and can then be tightened for increased safety with a Phillips head screwdriver. By swiveling the handlebar, the tricycle steers in the same manner as any standard cycle. Surrounding the rubber grip there are two twist shifters that control the front and rear derailleurs. They are placed in an orientation such that the user does not need to remove their hand from the handlebar to shift gears. There is a brake coupler located just in front of the grip, allowing the user to activate both brakes with one lever, requiring less force than a single brake on an existing cycle.
One of the most crucial advantages of our design is the ability to detach the one-handed control system, and restore the cycle back to its original two-handed function. This is especially important for adaptive cycling organizations that have a limited number of cycles, yet a variety of needs from participants. The gear cables have been cut allowing for the incorporation of two possible inputs (the one and two handed shifter) to each derailleur, connected via a barrel adjuster with calibration capability. The one-handed hook is simply slid out of the input side of the barrel adjuster, and the two-handed hook is re-installed. The brake cables can be unscrewed from the brake coupler, and returned to their individual initial locations. Lastly, the handlebar clamps can be loosened, allowing our handlebar to slide out and be completely removed from the cycle.
To test our device we first made measurements relating to all pertinent CPSC safety guidelines for bicycles. We measured the force required to apply brakes, the distance from handlebar to break lever, and the braking distance. For the brakes to be considered safe, the cycle must be able to come to a complete stop within 15 ft when travelling at 15 mph with a 150-pound rider. For this test we attached a speedometer to the cycle and accelerate to 15 mph. We marked a line where the rider should apply the brakes, and measured the stopping distance from this line. We found our average stopping distance to be 13.44 ft. A z-test was performed and we determined with 99.9999985% confidence that our stopping distance is less than 15 ft. To determine the success of our metrics that are more difficult to measure, we created a test course in a nearby park and asked volunteers of various age, height, athletic ability, and cycling experience to use our device and fill out a survey. The average age of our volunteers was 34.6 with a standard deviation of 19.1 years. The survey pool included 7 females and 6 males. 12 volunteers were able bodied, and 1 was a stroke survivor (end user). The bike received scores indicating above average performance for all metrics (minimum of 7 out of 10 for each category).
Costs & Implications
To create our prototype, it costs our team $140. In order to reduce this cost, we plan to partner with a cycling manufacturer. This would be advantageous because a cycling manufacturer could get most of our parts at significantly reduced costs. Additionally, they would already have equipment necessary for more advanced machining techniques. We estimate that a cycling manufacturer could reproduce our device for less than $60. The only company that sells a device that would compete with ours, sells their device for $1900. This means that we would be able to market our device at an extremely competitive price, and ultimately meet the needs of more individuals.
Our device solves a problem that no other device on the market adequately addresses. Our testing data indicates that our design is both safe and effective. Additionally, our design process has generated a product that is designed for reproducibility and manufacturability. Moving forward, we hope to get the Mono-Mano control system into the hand of all those who need it.
We would like to thank Prof. Amy Lerner, Prof. Laurel Carney, Prof. Scott Seidman, and Labratory Engineer Art Salo for their guidance throughout the design process. We could not have succeeded in the project without their continued support and guidance.