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The goal of our design project is to create a accessible rocking chair to fit the specific needs of a three year old girl with Retts. The nature of the girl’s condition requires a special chair that would give the girl the ability to exercise her gross motor skills while still supporting her head and neck. Other features of the chair will aid in restraint and provide the child with a comfortable place to eat and play.
Claire has Rett Syndrome, because of this her mobility suffers. Claire needs an adaptive rocking chair so she can continue to use her muscles and fight the mobility loss.
For this project we have a few specific needs that need to be met. Number one we need to design a chair that allows her to use her legs to rock herself. This is because the more that she uses her legs it will prolong the deterioration of her muscles. This means we need a chair with a platform that she can push off of or use the floor to push off of. Number two we need a comfortable head rest and seat. The head rest is important because her head could hit the frame while she is rocking. We will probably end up using foam padding and cloth in order to cushion her head so that she can rock and stay safe. Her mom said that when she rocks in her highchair, she will rock it across the living room. We want to make our chair have a strong and maybe heavy base in order to keep her rocking chair in one place. In addition to this we will most likely add an optional lap belt so that she will be securely in the chair.
Rett syndrome is a genetic neurological disorder primarily in girls. This disorder causes severe loss of motor skills and impairements in areas such as speaking, walking, eating, breathing, etc. Because of this, we researched different methods in which we could help our rocking chair the best fit. We first started with researching basic designs of rocking chairs we could then modify to fit our needs. Then we started researching ways we could build our own rocking chair to best accomadate what what we needed. There are a several companies that make adative rocking chairs for kids, but these chairs tend to be extremely pricey and unaffordable for the families. We found some models of chairs that we thought we could base our chair off of and modify to fit our family’s needs.
Bean Design:
This design utilizes a bean shaped frame to ensure the rocking chair does not tip forward or back while rocking. The chair part of the design will have padding around the body and head to provide protection during bodily rocking. A removable tray will go across the lap to allow for snacks and other activities. A lap strap will be added to the chair to help keep Claire in the chair while rocking. A rubber layer will be added to the bottom to prevent from the whole chair moving around and to protect the surface the chair is on.
Shock Design:
This design is composed of stationary base, a pivot, and padded chair. The stationary base will allow for aggressive rocking without the chair moving around the house. The chair will sit on a pivot point that is attached to the base. There will be a shock attached to the back of the chair connecting to the base to allow damping of the rocking movement.
Adjustable Seat Angle Design:
This design uses the typical curved base of a rocking chair. There will be a removable tray across the lab area to used for other activities, snacks, and more. Arms rests will be go along the side of the chair for arm support and safety. There is a lap belt to ensure further safety while rocking. The seat will have a hinge at the bottom of the back support to allow the seat angle to adjusted. To adjust the seat angle, you will move the rear seat support closer to the chair for a steeper seat angle or further away from the seat for a lower seat angle.
In order to make a final decision for our design we enlisted the help of our kids mom. We 3-d printed mini design models of concept designs 1 and 2. We took these to her house so that she could look at them and get a feel for what was going to work better for her. She ended up liking the concept design with the base and the shock so that is what we decided to move forward with.
Our selected design is built on a 2×4 base. The seats and the sides are made of 1/2″ inch plywood. We have a rod and bearings that allows the seat to rock back and forth. We have a shock that connects to the seat this dampens the rocking motion. We are also adding padding and fabric to make the chair more comfortable. A removeable tray will also be added so that she can eat off the tray if she wants.
Base and Shock: The base will be made with 2×4 wood planks and will located at the bottom on the interior of the main chair walls. It will be 22″ wide and 36″ long. Putting the base here, allows us to put more supports for rigidity, removes some pinch points, and allows for more degrees of rotation. We chose to use a shock off of an outdoor rocking chair. We went with this shock because it does a great job at dampening without worrying about rebound.
Chair Frame: The chair frame will be made from 1/2″ hardwood plywood. The walls will have a tear drop/bean look to have a more playful look. The seating area will have a seat that is 24″ wide and 12″ deep, and the back will be 24″ wide and 23″ long. The base and back will be connected to the side walls by notches cut into the sides of the wall and seating area. These notches will be cut using a laser cutter.
Bearings and Bushings: There will be 4 Low-Profile Mounted Sealed Steel Ball Bearings that will connect the piping to the chair walls. These bearings allow for smooth rotation and easy attachment. There will be 2 Vibration Damping Routing Clamps that connect the base to the lower rod, and 2 that connect the upper rod to the back of the chair. These clamps will keep rods from rotating and ensures that the wood does not wear down over time from metal rods.
Padding and Headrest: The cushion will be made of semi-firm foam with polyester fabric covering it. The foam will be glued to the chair base using upholstery glue. the fabric will be wrapped around the foam and stapled to the back.
Removeable Tray: The tray will be removable and washable. The pins and locking mechanism for the tray will be fabricated by the team. The tray itself will be order and fitted to the chair.
This engineering analysis deals with the rods that connect each side of the shock. The bottom rod runs into the 2×4 base, and the top rod runs into the plywood sides. This is a simply supported beam with a single point load in the middle. I decided the calculate the max deflection in the rod in order to make sure that the rod I chose would be able to handle the loads it would be put under. The results I found tell me that this 5/8″ rod will bend less than 2 thousand of an inches under normal working conditions. This means that this rod is plenty strong enough for this application. We made have to adjust the rod based on the size of the shock that we get however the rod size will not change much. If it does, we will only need to change one value in order to find the new deflection
The choice of foam is an important consideration for the chair. Upholstery foam comes in many firmness varieties. The foam I chose has an indentation load deflection (ILD) of 35. This is a measure of how much weight (lbs) it takes to compress a 50 in^2 patch of foam to 25% of its original height. For chairs, the recommended ILD is about 44 however, since this chair is being made for a child, I decided to use ILD 35.
The tray is removable and dishwasher safe. It is connected to the chair with a pin locking mechanism. This tray is easily washable and spill resistant. The built in cup holder and raised edges are a large reason this model of tray was selected.
The tray can be modeled as a simply supported beam. This means the pressure put on the tray is supported by both sides of the chair’s frame.
Buckling is also not a concern. This is because of the structure of the tray and the raised edge. An easy way to think about this is to view the tray as a ruler. When flat the ruler bends when pressure is applied, but when set sideways a ruler will not buckle. The raised edges design of the chair acts like a ruler on its side.
Base and Frame Fabrication: We assembled the base using 2x4s. We then used 1/2-inch hard wood to cut the sides of the chair. We cut them using the lazer in the shop. We made it where they would fit together perfectly. We then used wood glue and screws to attach everything together. We fabricated a shock mount to attach the shock to the base. We used a shock from a rocker chair. This worked perfect because the spring constant was the correct stiffness. We used the top mount taken from the chair to attach it to the chairback. We then painted it to give it some color. We attached some trim pieces to make sure everything looked good. The paint and flowers added a nice touch. We used a 3d printed stencil for drawing the flowers.
Foam Fabrication: The foam was measured to fit into the chair. It was then cut with a bandsaw. The wood base of the foam was cut to be slightly smaller than the foam. The wood and foam were then glued together. Finally, the cloth was stretched over the foam and stapled to the back. The finished cushions were then secured to the main frame with nails.
Tray Fabrication: The Tray was ordered online and adapted to fit the chair. The chair has two mounts placed into the back. These support the rods, which were adapted to fit the tray, were then attached to the tray. The tray is removable and washable.
The chair was tested by having multiple team members sit and rock in it. Since the chair is meant for a small child, this test was more than enough to prove the chair’s strength.
The instructions for use are very simple with just a small note to be aware of the potential pinching points that are common to rocking chairs. The tray is inserted into the tray holder holes with no need to be fixed with a clip since the holes are just the right size to hold it secure.
This project has taught each one of us the importance of careful design and communication. Throughout the semester, we had to be in constant communication with each other and the client to make sure the chair would successfully fit together and function properly. We also had to ask the machinists for advice on the best way to bring our designs into reality. This design process was something new for some of our team members and has undoubtedly been a valuable lesson.
