HCDS- Adaptive Seating System for use on Sleds
Cerebral palsy is a condition that affects one’s posture, muscle tone, and mobility . From person to person, cerebral palsy varies in symptoms and strength of symptoms including, but not limited to, mobility issues, speech, hearing and learning difficulties, and spinal deformities. Out client, Birkley, has had cerebral palsy since birth due to a viral infection. Birkley is able to walk on her knees and more recently standing up, but due to her left side weakness has some troubles walking and standing upright for extended periods of time. Birkley’s mother, Tamra, would like to keep her involved in family activities, and would like an adaptive sled for Birkley to use.
Currently, only one adaptive sled serves this market; this design is very expensive ($600) and looks similar to a dog sled .
Our goal for this project is to create a seating system that works with a common type of sled. This design will provide the support Birkley needs to prevent her from sliding down or tipping out of the seat and it will cost less than $200.
Design constraints specify that the seating system should work with a sled and other recreational activities, weigh less than 50 lbs, and be able to fit a 5’, 125 lbs child at the maximum. This team will design and develop a working prototype available by February 21, 2020 and a final product to be delivered by May 1, 2020.
- Naya Ziegler
- Margaux Wheeler
- Gabe Maestas
- Griffin Stanton
- Ryan Meraux
- Nick Gardner
- Tamra Logan
Project Advisors: Joel Bach & Chelsea Salinas
Client: Tamra & Birkley
Thank you to our clients Tamra and Birkley for providing detail and feedback on our designs. Thank you to our project advisors Joel Bach and Chelsea Salinas for guiding us throughout this project.
Hello and thank you for taking a look at the adaptive sled for the HCDS Capstone! Our team was tasked with designing a seating system for use with a sled for a girl with cerebral palsy. Our client, Birkley, and her mother, Tamra, wanted a lightweight, stable, supportive, and cost efficient sled that would allow for Birkley to sled down their neighborhood hills independently. This project was started last semester and continued on by a new team this semester. For this semester, we took the latest prototype and redesigned it to fix some of the major concerns and issues for Birkley. By using center of mass calculations, tipping calculations, weight testing, and prototype testing, we were able to design an affordable seating system that can attach to a common utility style sled with ample support without the use of straps, seatbelts, or pommels. Our design features a fabric seat on a pvc frame built to provide hammock support for Birkley so that she cannot tip side to side, as well as a reclined seat to prevent her from falling or slipping forward. In the future this seat can be adapted to have an adjustable angle and can be modified to be attached to various outdoor equipment such as a paddleboard.
Last semester, the team did some initial brainstorming and settled upon a prototype using a wooden sled and a racing seat. In January, our team met with Tamra to discuss some of the issues with that prototype. From our meeting with our client, we discovered that size, weight, and stability were some of the major concerns about the previous prototype. We used this feedback to help construct a new prototype. During our meeting, Tamra also showed us Birkley’s Rifton bath seat for inspiration. This seat is designed for Birkley’s height and weight; it features a plastic frame with a mesh seat and straps to hold Birkley while she is in the shower . See figure 2.
Knowing that Birkley is 80lbs, 4’4”, and approximately 26 inches in the waist, the correct Rifton seat for Birkley is the medium sized seat. Because this seat is smaller than the previously used racing seat and it is made for Birkley’s size, we decided to use Birkley’s bath seat for inspiration. we then had to determine how to ensure that our sled is stable and light weight.
In order to improve stability, we calculated Birkley’s center of mass while sitting and determined the width of the sled necessary to prevent her from tipping in the worst-case scenario (45 Degree slope). From these calculations, it was determined that the width between the sled tracks of the wooden sled would need to be at least 29 inches. The wooden sled used from the last semester was only 15 inches wide. Our team then decided to see if another type of sled will result in smaller dimensions. It was determined that a utility sled is the best option for our design. Tipping calculations determined that the distance needed to be at least 17 inches wide to prevent her from tipping sideways in a utility sled.
In addition to adding stability, the combination of a plastic utility sled and a smaller seat would also improve the size and weight concerns.
Figure 3: Shappell Utility sled used for our seat design.
Figure 4: MatLab code for center of mass and tilting calculations
In order to keep the final cost of the adaptive sled low, we decided to build the seat frame out of PVC piping. The seat is made from a water resistant canvas material. This material is durable and strong, and it will hold up in the winter elements.
Unlike normal adaptive seats, our seat does not require any seat belts, straps, or pommels because it is tilted back and has a raised bottom. Newborn carseat guidelines suggest that the tilt of a carseat can be set anywhere from 30 to 45 degrees to protect the baby . While Birkley is not a newborn, the tilt provides the same support for her on the sled. Unfortunately, the angle for the seat is not adjustable, so to account for the worst case scenario of a steep sledding hill, the angle of our seat has been set to 45 degrees. While the tilt of the seat prevents Birkley from falling forward out of the seat, the sides of the sled and the canvas create enough side support to prevent her from falling to the side (the fabric allows the seat to have side supports like a hammock would).
Figure 5: Front Profile of seat frame
Figure 6: Full view of seat frame
Figure 7: side profile view of seat frame.
The seating system is mounted with four bolts on each side of the sled. These bolts go through holes drilled in the lower PVC piping and the side of the sled. To add additional support, the upper back of the seat is supported by two pvc beams that sit in the tracks in the bottom of the sled. The sled our team used is 21in wide, 43in long, and 8in deep.
Throughout the build of our final prototype the system was tested to ensure that it could hold at least 125 lbs, would not tip over during static and dynamic situations, and remained small enough to fit inside the back of a standard suv. See gallery for pictures of the final prototype. The total cost of the sled system is $70. The breakdown of materials purchased can be seen in table 1.
Table 1: Bill of Materials
The design of the seat can be further improved in the future by adding some adjustments to the angles and positioning of the seat in the sled. In order to fit more user’s needs, the seat recline should be adjustable. Adding a hinge joint that would allow some movement in the incline would achieve this goal. A similar device can also be adopted in the bottom of the seat to alter how high the user’s knees would be while sitting in the sled. Another future improvement for this design would be designing an attachment method that would allow the seat to be separated from the sled in a shorter amount of time.
 “Cerebral palsy – Symptoms and causes”, Mayo Clinic, 2019. [Online]. Available: https://www.mayoclinic.org/diseases-conditions/cerebral-palsy/symptoms-causes/syc-20353999. [Accessed: 11- Oct- 2019].
 “Adaptive Snow Sled”, Flag House, 2019. [Online]. Available: https://www.flaghouse.com/Recreation/Winter-Fun/Adaptive-Snow-Sled.axd. [Accessed: 11- Oct- 2019].
 “The Wave,” Rifton. [Online]. Available: https://www.rifton.com/products/bathing-and-toileting-systems/rifton-wave-z220. [Accessed: 22-Apr-2020].
 “Infant car seats – Get the angle right,” Product Reviews and Ratings – Consumer Reports, 09-Sep-2011. [Online]. Available: https://www.consumerreports.org/cro/news/2011/09/infant-car-seats-get-the-angle-right/index.htm. [Accessed: 02-Apr-2020].
Meet the Team
Naya is a senior in Mechanical Engineering with minors in Public Affairs and Biomechanical Engineering. She will be returning to Mines in the fall to earn her Master’s Degree in Biomechanical Engineering.
Margaux is a senior in Mechanical Engineering. she will be graduating in May 2020. Margaux loves horses and plans to move back to Oklahoma after graduation.
Gabriel is studying mechanical engineering. He plans to continue in his education to receive a Master’s in Solid Mechanics. Gabe is particularly interested in the mechanical behavior of composites. In his free time, Gabe likes to get outside to go camping, fishing, off roading, or working on personal projects.
Ryan Meraux is a mechanical engineer major from New Orleans, LA. He really enjoys fishing, target shooting, skiing, and being with my family and friends. Ryan hopes to one day work in the aerospace industry, but for the time being, he is currently planning on getting an MS in Mechanical Engineering.
Griffin Stanton is studying Mechanical Engineering and plans to graduate in May of 2020. he enjoys hiking, snowboarding, fishing, and spending time with friends and family. Throughout college, Griffin has pursued work in the oil and gas industry and plans to hire on with ExxonMobil fulltime in September of this year. Griffin’s experience at Mines has taught him to be diligent and hardworking but also to enjoy the down time (few and far between as it may be) to the fullest.
Nick Gardner is a fifth year senior at Mines graduating with a Mechanical Engineering degree in May of 2020. He is a redshirt senior on the varsity baseball team at Mines, participating all 5 years on the team. He is set to start working as a project engineer for Phillips and Jordan in the summer after graduation.