Rugged Outdoor Asymmetric Wheelchair
The objective of this project was to design a wheelchair that could be taken on hiking and fishing trails in a manner that would not impede the independence of the user. The team was tasked with working with QL+ in order to design a wheelchair for the client Gary Verrazano. Gary is a double amputee Marine Corps veteran. He lost his right arm and right leg in a work related accident, and is now using a combination of a wheelchair and a prosthetic leg for mobility. As Gary maintains an active lifestyle he needs an off road-road rugged wheelchair. Trail terrain is difficult to traverse, so the wheelchair must have a mechanical advantage.
- Robert Gambrell
- Matthew Lavengood
- Matt Kinney
- Nic Pythian
- Cammi Benson
- Ian Chang
- Mikaela Salzetti
- QL+ working with Gary Verrazano
The team would like to thank Gary Verazzano for being willing to work with us, and for all of his design input. Thank you also to QL+, specifically Court and Scott, for their support of the project. Finally, thank you to Donna Bodeau for keeping us honest and for being a great PA.
Gary Verrazano is a double amputee Marine Corps veteran. He lost his right arm and right leg in a work related accident, and is now using a combination of a wheelchair and a prosthetic leg for mobility. As Gary maintains an active life style he needs an off road-road rugged wheelchair. The project was to create a rugged off-road wheelchair for Gary to take on outdoor trails to go fishing. Trail terrain is difficult to traverse, so the wheelchair must have a mechanical advantage. The wheelchair features off-road mountain bike wheels, a lever arm for propulsion, foot pedal brakes, a rear differential, and an emergency hand brake. The asymmetry of Gary’s body was paramount in every design decision. As this is a custom design, it was imperative that common off the shelf components were used whenever possible. This can be seen in the design with the incorporation of mountain bike parts in the wheels and braking systems. In addition, a special type of metal known as 80/20 aluminum was used in the chassis. This material relies on bolts and screws as connection points rather than welding or bending to create the chassis. This was important to the team so that adjustments could be made easily to fit the needs of the wheelchair user.
There were multiple important design considerations in the design process that resulted in design decisions. It was important to the team to be able to minimize custom parts in the wheelchair. This was important as it would allow for minimal adjustments if this wheelchair design needed to be retrofitted to another user. This meant that many of the subcomponents were created with parts that could be bought commercially, such as gears through McMasterCarr and standard mountain bike wheels and brake components. In addition to this, it was decided to create the chassis out of 80/20 aluminum. This allowed for all connections from subcomponents to chassis to be connected quickly and easily through the tightening/loosening of a couple bolts. It also allowed for adjustments in location of the seat and foot pedals which satisfies the goal of adapting this design to another user. Also, the ease of 80/20 connections also assisted the team goal to minimize excess fabrication time with processes such as welding and milling.
Design Concepts Considered:
The design concepts considered throughout this process mainly pertained to variations in the chassis and braking system. The chassis designs that were considered consisted of three main designs. The first design option would be to ruggedize an existing wheelchair by adding offroad wheels, larger front castor wheels, a range of seat tilt options, and disk braking components. The second design option was a chassis made from 8020 Aluminum that would support three wheels. This trike design was intended to be light-weight and mobile. The third and final design selected was another chassis made from 8020 Aluminum but this design allowed for four wheels. This quad design ensured the wheelchair to be more stable while still being mobile. Ultimately, the third design of a quad wheelchair made from 8020 Aluminum was picked.
Much of the design process was based upon communication with the client. It was important to make sure that the components of the chair were oriented in a way that would optimize comfort and efficiency for Gary when using the wheelchair. Decisions such as seat width, foot pedal length, and lever arm location were based upon physical measurements of Gary. For more complex components such as the differential, smaller 3D printed models were made and tested to ensure that the larger models would perform appropriately.
To make sure that the design would be feasible, it was compared to pre-existing products and also went through FEA using Solidworks. By comparing the design to already existing products, a sense of size and weight limitations could be established. This paired with client input gave a set of guidelines for size and weight. FEA was then run on all major parts that could fail. The axle, lever arm, and wheel connections all had FEA performed on them to make sure that they would not fail under load.
The main way that information flows through the prototype is shown in the flowchart above. The driver of the wheelchair will decide what direction they want to go, and then use the lever to drive a differential. There will then be brakes attached to foot pedals that can grab each wheel individually. This will cause the wheelchair to turn thanks to the differential axle allowing both wheels to turn at separate rates. As one wheel cannot turn, the wheelchair will then pivot around that wheel. Similarly, the wheelchair can go in reverse by rotating the ratcheting lever 180 degrees.
This design offers a one of a kind wheelchair to the user and is effective in meeting the requirements that Gary listed. The manual power assist offers a easy form of power transmission that will allow the chair user to move with an efficient lever pull. In addition, the braking system offers a braking opportunity to assist the user on hills as well as to assist in turning. The use of 80/20 aluminum provides a lightweight, yet extremely strong, frame for the wheelchair. This 80/20 material also allows for easy adjustments of the seat and foot pedals as well as the option to attach any other components in only a few minutes.
Due to the current situation, the team was not able to finish the project. It will be continued next semester by another team, who will finish the assembly and conduct testing. The project has been made easy to pick up from where it was left off as build instructions have been created and all parts cataloged and numbered. The design process that has been outlined throughout this project can also give future groups an idea of how it was assembled, if they feel that they can improve upon it. After construction, testing would need to be carried out. Tests such as braking distance, force to move the lever arm, tip angle, turning radius, and how far a single pull of the lever arm moves the chair would all need to be tested, both without our client controlling it, and then with our client controlling it.
Meet the Team
Robert is a senior studying mechanical engineering with a minor in business and entrepreneurship. In addition, he is on the Mines Wrestling team and enjoys spending time outdoors. This project caught his interest because it offered the opportunity to engineer a one of a kind wheelchair design while simultaneously solving a problem for Gary.
Cammi is a senior studying mechanical engineering. She is the President of the Mines Equestrian Team, a member of the Mines Club Ski Team, involved with Teach at Mines and SWE. She chose this project because it offered a unique opportunity to design an almost completely new product that has the potential to really help Gary.
Matthew is a senior studying mechanical engineering with a minor in computer science. He is on the Mines Wrestling team and enjoys spending time with his dog.
Ian is a senior studying mechanical engineering. He currently works in the international office on campus, helping incoming international students with their visa work. After college he plans on spending a year in grad school to obtain his master’s in mechanical engineering with a focus on fluid and thermal flow.
Nic is a senior studying mechanical engineering who has a passion for rapid prototype design/build projects. He chose this project because he saw an opportunity to put his creative abilities and problem solving skills to the test as well as make an impact in the community of veterans.
Mikaela is studying mechanical engineering at the Colorado School of Mines who came here from Alaska. She has a love for the outdoors and likes to spend her time skiing or camping.
Matthew is a senior studying mechanical engineering, and a teaching assistant at the School of Mines machine shop. He chose this project given that it allowed an opportunity to work on a design that not only has the potential to better Gary’s life, but also help many people struggling with similar situations.