Anand Mhatre, Herbert Hill, Kalai Tsang, David Smeresky, Ashlee McKeon, Thomas Bowers, Elaine Houston, Greta Brecheisen, Dan Osaque, Sarah Bass
Our client desires to return to fully participating in the sport of sled. He has hemiparesis on his right side in addition to carpel tunnel and a shoulder injury and therefore, struggles to attain and maintain game speed while playing due to not being able to propel and navigate his sled using both hands as most current players of the sport do. To address these participation restrictions, our team is developing a recumbent adaptive sled design by modifying the users’ current sled. This design incorporates a bicycle style drive system that allows for propelling the sled with one leg and rudders like snowmobiles to allow for effortless turning. Our main objective is to design and produce a functional prototype that meets our client’s needs and allows for maximum participation during game play.
Sled hockey is a fast growing Paralympic sport where athletes propel and navigate a sled as shown in Figure 1 while trying to guide a hockey puck into a goal. The game rules are very similar to stand up hockey with adaptations for play in sled. The user sits in the bucket that is mounted on two blades with his feet and legs stretched out in front on the footrests. Two sticks are held in either hand to push the sled against the ice in a rowing style motion. Traditionally, this sport was developed for individuals with disability in the lower limbs, utilizing upper body function; however, with more and more individuals with disabilities affecting both an upper and lower extremity who desire to play sled hockey, this set up does not allow for full participation in the sport.
Figure 1. Ice Hockey Sled
Our client is middle-aged male with cerebral palsy (CP), which causes him to experience hemiparesis on the right side of his body and makes his limbs subject to contractures and flaccidness. He also has carpal tunnel in his left hand and has some residual effects from a previous shoulder injury. These functional impairments, make it impossible for our client to hold two hockey sticks simultaneously in while playing sled hockey as the sport traditionally requires. Consequently, this has negatively affected his game play and made him unsatisfied with his participation level. In order for our client to play at optimal game speed and keep up with his teammates, modifications to his current sled need to be made. Our team is designing and building an adaptive sled so that our client can participate in the game of sled hockey as he once did. It is our hope this design solution, if successful, could be further modified and made accessible to other one- handed sled hockey players.
To deliver an efficient sled design to our client, we implemented a client-centered product development process. With this, we were not only able to integrate client concerns needs, and wants into the design but, we were also able to involve the client as an active team member throughout the process. Our project team consisted of rehabilitation engineers, and clinicians for a multidisciplinary approach. We were allotted $500 for the development and fabrication of our sled design. This project is being carried out at the Human Engineering Research Laboratories (HERL) in the University of Pittsburgh’s Department of Rehabilitation Science & Technology in Pittsburgh, PA.
Figure 2: Design Specifications
In the initial phase of this project, the client’s needs and wants in an adaptive sled were captured through interview. Beginning to work collaboratively with the client, our team focused on getting to know him personally and understand his vision of the finished product. The data obtained during this interview was transformed into a design specification sheet as shown in Figure 2. These specifications based on client preferences allowed us to cultivate multiple design concepts that focused mainly on sled driving (propelling) and turning (navigation). Each concept was then evaluated using a concept-screening matrix against the criteria of sled speed, navigation, game rule compliancy, safety, feasibility, durability, etc. Concepts that scored the best on criteria in the matrix were then hand drafted (Figure 3) or physically modeled (Figure 4) on a small- scale for presenting to the client. The feedback received from the client on these designs contributed to further iteration and filtering of our concepts. Our team visited some sled hockey games to observe game play and integrate insights into the design process.
In the next phase, our narrowed designs were grouped into modular concepts, which were then evaluated for technical feasibility, durability, adaptability and cost-effectiveness. Designs were further constrained after the client was asked to undergo some anthropometric and physical function measurements preformed using a dynamometer, goniometer, and a line gauge. Collaborating with our client during such an iterative development and evaluation process helped us to ensure that our design concepts reflected the client’s satisfaction at each part of the process.
Lastly, following rigorous brainstorming between our team, faculty and engineering staff at HERL, complete sled models were selected and presented to the client. Eventually, a sled design concept utilizing a foot-powered mechanism for propulsion and a pivoting bucket mechanism for steering were selected as final design concepts. The foot propulsion mechanism includes a pedal connected to a crank similar to the setup of a bicycle, which drives a wheel mounted beneath the sled bucket similar to that shown in Figure 4 but closer to the blades. For steering, a pivoting bucket balances on springs and is attached to plastic or rubber rudders on both sides that will come into contact with the ice creating friction for adequate turning as shown in Figure 5. The client will be handling the puck using a stick in his left hand.
Figure 3: Few of the hand drawn sketches presented to the client
Figure 4: LEGO prototype to display the idea of moving or rotating blades of sled
Figure 5: Pivoting bucket with rubber rudders on sides
Concept Prototyping, Evaluation, and Fabrication
The design team was split into three groups – sled- navigation group, sled- ice Interface group and sled- user interface group for testing individual design concepts and fabricating prototypes. The teams began by developing physical prototypes of estimated final design. The sled- user interface group built a pedal- crank prototype using duct tape and PVC piping to gain perspective on the size of the front end of the sled and how it would affect driving. The sled- navigation group created a small- scale prototype of a pivoting bucket using toothpicks and clay to display turning functionality.
With regards to design concept evaluation, the sled- ice interface group tested wheels of different designs as shown in Figure 6. The wheels were evaluated on a test setup as shown in Figure 7 for determining friction coefficients and consequently, to calculate torque and power numbers for the system required to drive at competitive speed. This testing gave insight to the optimal wheel design for maximum traction on the ice. Wheels with deeper treads and studs on the periphery provided the needed force and traction. Following testing and evaluation, all groups performed design calculations and derived frame and part sizes while keeping the rules and regulations of sled hockey in mind.
Figure 6: Various wheel designs for evaluation
Figure 7: Test Setup to find friction coefficients of wheels shearing through ice
Each group modeled their design concepts in SolidWorks and a finite element analysis was conducted on the sled assembly to determine the weak stress points due to the force inputs. At the same point in the process, the simulated model of the sled was presented to the client to obtain his feedback on the design before fabrication. He expressed concerns pertaining to the safety of the sled user (himself) when coming in close contact with other players, which were then addressed in the model design. The SolidWorks model as shown in Figure 8 was updated iteratively upon consultation with faculty and engineering professionals at HERL to include easy-to-fabricate parts. Along with this, the team simulated design concepts in SolidWorks that reflected an adaptable version of the sled. This version includes switching the pedal mount between the right and left sides and adjusting the tubing frame for use by other players with different functional needs than our client.
Figure 8: SolidWorks model of Ice Hockey Sled
Materials required for fabricating the sled were ordered from an industrial supplier and bicycle parts were obtained from used bikes purchased from a local bicycle recycling facility. A full scale prototype as shown in Figure 9 was developed in the machine shop at HERL with each group fabricating the components as displayed in Figure 10.
Figure 9: Full scale prototype of Ice Hockey Sled developed by the team
Figure 10: Sled parts fabricated by three groups of the development team
Discussion and Conclusion
Ensuring maximum participation for people with disabilities in their environments is one of the main aims of rehabilitation science. Our client loves the sport of sled hockey and faces difficulty playing due to his functional limitations. With this design project, we attempted to build a fully functional prototype that assists our client with propelling at competitive speeds and turning effortlessly. Working collaboratively with our client during the design process from concept generation to fabrication was critical in order for us to provide a design solution that not only met our clients’ needs but can also be adaptive for use by other players with similar functional impairments.
The equipment was developed based on design specifications established early on in the process. The sled is lightweight with a rigid, durable frame made of aluminum and steel parts. The sled has the capacity to accelerate to game speed, adheres to the 2- limb rule of sled hockey, and supports easy turning. The cost of modifying a more commonly used sled to our design can be estimated to be less than $250. Most modifications on the sled are designed for manufacturability and repeatability due to the use of standard bicycle components. Our sled is a new design concept in the field of sled hockey for one-handed players and although our prototype seems to efficiently address our client needs in its current state, we need to conduct field testing that will allow him to interface with our design to be sure.
Client testing will be conducted to determine the appropriate fit between the user and our design solution. As with any rehabilitation engineering design process, our team anticipates client testing in the natural environment will shed light on areas for modification and improvement of the sled design. We expect an iterative design of the sled until we can ensure the most optimal user interface with our device to meet the needs of our client.
Additionally, we look forward to implementing the concept of universal design. Since we began working with our client, he has expressed a greater desire for a sled design solution of this type (functional for one- handed sled hockey players), to be functionally adaptable to the needs of other one- handed players. This goal focuses on extending the accessibility, safety, and convenience of our design to individuals who otherwise would most likely be restricted from participation in the sport of sled hockey. Keeping this goal in mind throughout our inclusive design process, our team developed design concepts with current sled parts that can be moved, altered, and adapted to fit functional differences seen across one-handed sled hockey players. These design concepts will be integrated into our design revisions once testing of the current prototype is complete. Future efforts to extend our design to other one-handed sled hockey players will require additional user testing and modifications to ensure to correct fit, and we feel confident the universality of our design will impact sled hockey players on a much larger scale.
Our design team is greatly thankful to the HERL faculty and staff, especially, Dr. Jon Pearlman and Dr. Mary Goldberg for their guidance, support, and direction throughout this project.
We would like to acknowledge the machine shop staff at HERL for their continuous support in designing and fabricating the components of our design.
Finally, our team would like to give a direct a special thanks to FreeRide and Performance Bike Shop in Pittsburgh, PA for their courteous advice on the selection and integration of bike parts into our design.