college of engineering white

Project 5: Supportive Wheelchair


Our goal is to design a new wheelchair for an eight-year-old boy with cerebral palsy.  The family and teacher are concerned that the current wheelchair is allowing the child to slouch and shift his weight in his seat, causing problems such as a need for hip replacement, feet not staying in the footrest, and restraints causing skin irritation and discomfort. The headrest is fixed and rubs on the child’s head causing a bald spot, and the current removable activity tray is difficult to remove and attach.

Hamza Ansari, Helaena Pfeiffer, Hailie Pippin, Ayla Render, Kaleb Sanford, Jane Vassar

Problem Statement

Cerebral palsy can increase muscle tone and lead to spasms in the limbs. The child has generally increased tone in upper and lower extremities and fair head and trunk control. He is dependent in transfers and mobility and is incontinent. He also presents with a flexor synergy pattern and often struggles with independence. Due to this, our wheelchair will need special support to the torso, hips, and legs. For this project our team will be designing and developing a new wheelchair that will add support for muscle tone, minimize skin integrity issues, increase independence, and have a personal flair.

To help support muscle tone, the chair will need to prevent the child from being able to slide out of the proper 90 degree sitting position or unevenly distribute his weight. This positioning will be even more important after the child’s hip surgery in the coming year. Improper positioning can cause the hip to dislocate after surgery. To minimize skin integrity issues, a comfortable and easy to clean material will be needed and the seat restraints may need to be redesigned to reduce friction. We also have a goal to better facilitate his independence. We want to make it easier for him to participate in class and work on skills such as learning to feed himself.

Design Specifications

  • Adjustable seat that tilts while maintaining proper 90-degree hip position
  • Adjustable/removable head rest
  • Easily removable activity tray with smooth top
  • Chest support paddle cushions
  • Comfortable support straps
  • Adjustable foot tray
  • Easy to clean material
  • Able to grow into
  • Blue

Background Research

Our family’s child has spastic cerebral palsy. We did some research on the symptoms and difficulties that come along with his condition so we could better understand the type of adjustments he may need for his wheelchair to make him more comfortable. We also talked to an Occupational Therapist (OT) who specializes in fitting children and their symptoms to wheelchairs and aftermarket products. We discussed the needs of the child and were recommended various strategies to think about when designing and building our own. She also suggested we talk to an Assistive Technology Practitioner (ATP) in our area once we have concept designs.

We also looked into wheelchairs and products currently on the market and determined that the wheelchair that meets all the current needs except the activity tray is the Zippy Tilt-in-Space wheelchair technology.

Below are local ATPs and their contact information:

Concept Design 1

Adjustable Tilt Wheelchair with Tray

  • buy a new wheelchair that already fixes some of the main issues. The Zippie Iris is a top of the line wheelchair that costs $3147 and has the following features:
    • 40 – 55 degrees of tilt
    • Folding cross brace that allows the chair to be folded for easy transportation.
    • Growth capabilities, ability to adjust to continue to bring support as the child ages. the company also provides a free growth kit so the chair can be adjusted.
  • Design and attach activity tray


  • Able to give a wheelchair that meets all its needs without us having to design a fix for each problem.
  • Able to focus on our designs to make sure all possible issues with the wheelchair are fixed.


  • Very expensive, this concept will have the largest budget.
  • We wouldn’t be doing much problem solving ourselves unless there were additional problems listed.


Concept Design 2

Reconstructed Adjustable Tilt Wheelchair from Static Model

  • Design and modify full adjustable tilt with solid backrest shell, side supports, and solid seat cushion
  • Lap restrains parallel to seat
  • Adjustable removable headrest
  • Removable tray
  • Upholster with Naugahyde


  • Cheap
  • Adjustable tilt and headrest


  • More work to fabricate
  • Potentially less durable
  • Less portable

Concept Design 3

Fixed Tilt Wheelchair from Static Model

  • Taller front caster wheels to create a fixed seat tilt
  • Removable back with side supports and removable seat for easier transfer
  • Removable headrest
  • Parallel lap restraint
  • Removable tray
  • Upholster with Naugahyde


  • Easier to fabricate
  • Easier to store and transport
  • Maintains most features of original wheelchair
  • Can be further adapted


  • No adjustable seat tilt or headrest
  • Weight through hips and lower back for all the time in chair

Selected Concept Design

Concept 1 was the best based off the decision matrix; however it is outside of our expected budget and is therefore not feasible. Our next best option was Concept 3 with the second highest score on the decision matrix. We plan to add the adjustable head rest from Concept 2 to the design for Concept 3 to try to meet more of the goals requested by the family. Concept 3 was the best because Concept 2 was much more difficult to fabricate in our limited time this semester and the amount of failure points that would be introduced is too concerning to choose for a project that is only one semester long.


When looking for the base wheelchair that could be modified for Concept 3, we found a used tilt-in-space wheelchair within our budget. Our new plan is to make the modifications for Concept 1 as well as designing a full seat cushion spacer to account for the large size of the used wheelchair seat compared to what the child needs.

Decision Matrix

Overview of Selected Design

The design for our wheelchair takes an existing tilt-in-space wheelchair that is oversized for the small child that will use it. We are going to make a cushion seat spacer upholstered with Naugahyde and attach it with Velcro to the existing seat.  We will also design a removable activity tray with four straps to attach to the existing armrests.

Describe Design Details

Seat Cushion

For the seat cushion, the ordered wheelchair is 14×14 in. seat with a 15 in. back, and the child has a hip to knee distance of 12.6 in., a hip width of 8.7 in., and a top of shoulder to seat distance of 13 in. This leaves a 2.65 in. gap between each side edge of the seat and the child’s hips, a 2 in. overshoot between the top of the chair and the top of the child’s shoulders, and a 1.4 in. gap between the backrest and the child’s back. These gaps and overshoots cause safety issues for the child, so they need to be minimized.

The seat cushion spacer will be designed to account for the oversized chair while giving the child adequate support. It will essentially be a foam chair of the right dimensions for the child that sits fixed inside the ordered wheelchair to ensure proper body position. The design includes raised edges on the seat cushion to minimize sliding left and right in the seat, a full seat base to place the shoulders in the ideal position, a full backrest to promote the 90-degree hip angle, and additional extrusions on the backrest for promoting proper torso alignment.

The cushion will be upholstered in Naugahyde for easy cleaning and sanitation, and the use of Velcro will allow for easier transportation and removal when outgrown.

Activity Tray

The activity tray will be made of polycarbonate Lexan. Lexan has a smooth surface, is known for its impact resistance, and is able to be cut to size. The smooth surface will allow suction cups to be used for skill building activities and class participation. The tray is designed to lay over the wheelchair’s armrests and be fasted by 4 straps. There are 2 straps for each armrest and the fasten on both sides of the bar that hold the armrests to the chair. This and the compressibility of the armrest cushion allow the activity tray to stay on when various forces act on it.

Engineering Analysis 1

For our forces analysis, our main goal is to find out how much force is experienced at the strap connection points when weight is applied to the tray.  This helped us calculate the forces at each individual strap connection point and determine the type of material we should use. The tray and straps can be modeled as a simply supported beam.

Engineering Analysis 2

This force analysis is for us to see how much force the straps will need to withstand while reacting to the force applied to the end of the tray. This will also help us determine the specific material and type of strap to use on our tray.

Engineering Analysis 3

For our 3rd form of engineering analysis, we decided to use finite element analysis (FEA) to show the stresses in the tray when force is applied. We used Inventor for the stress analysis since the program has a built in FEA study. After developing the CAD model for the tray, the part file was put into the software. Constraints had to be set before running the analysis. The legs that attach to the arm rests were set as fixed ends, the part has been set to a material of Polycarbonate plastic, and a force of 100 lbs was applied to the end of the tray. The tray held up well, with bending stress at the connectors. We do not expect 100 lbs of force to be applied to the tray however, we want to make sure this tray will be built to last along with the rest of the wheelchair. The max force that can be applied to the tray before failure begins is 140lbs, which should be more than enough strength needed for the tray.

CAD Drawings

Bill of Materials

Document Fabrication Process

  1. We cleaned the chair and spray painted the purple metal with blue spray paint.
  2. We created a fixed tilt for the chair by raising the adjustable height of the front caster wheels by moving the bolts to a lower position.
  3. We added the chest restraint straps to the seat back of the chair using the clasps and adjustment straps.
  4. We used adhesive leather repair strips cut to size to repair the damaged cushions, headrest, and armrests.
  5. We fit the wheelchair to the child and marked the height for the footrest. We moved the footrest to the marked location by adjusting the bolt locations.
  6. We exported the tray drawing into a .dxf file then used that file to waterjet the polycarbonate tray. We initially consulted Chris Mills and planned to use a laser cutter but when we started the cut the material began to burn.
  7. We wrapped the activity tray in a blue, waterproof contact paper and ensured all edges were smooth.
  8. We then adjusted the activity tray attachment straps and cut them to be a more reasonable length.


Testing Results

Before fabricating the tray, we mocked up the design with cardboard and brought it to the wheelchair fitting we did with the child. We found that our design addressed all of the concern of the family. These goals had been a tilted seat to prevent the child from pushing out of the proper position, an easily removable activity tray, and footrests that were in the proper position.

Instructions for Safe Use

  1. Ensure that child is properly positioned in chair. Fasten straps and adjust to a comfortable tightness that will prevent pushing out of proper position. When adjust headrest and armrest height ensure the child is positioned so that he will not be pinched. When attaching activity tray, be sure that the child is positioned so that he will not be pinched. Do not exceed 50 lbs on the activity tray.


2024 Spring