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The family is in need of a motorized, adjustable activity chair for Avonlea. They are open to possible adaptation of the current chair that they have.
Our child has limited strength and mobility, and needs an activity chair to move around. The family would like a motorized chair to allow her more independence. In addition, they would like for the seatback, headrest, armrest, and footrest to be adjustable, and its height to be electronically adjustable. Their current chair has small wheels that have a difficult time going over rougher terrain like a gravel driveway, so they will need more rugged wheels. Weight is also a concern as it will need to be moved in and out of their car.
Our background research involved us analyzing Avonlea’s current chair and searching for different methods to improve her new chair to her needs. We first used her current chair, the Rifton Activity chair, for reference on some overall design concepts. We also looked into past projects that were similar to ours. As for the motor, we looked into pre-programmed drive kits for wheelchairs to attach to the chair. We also researched several methods to adjust the seat, head, and armrests for the chair with methods such as: hydraulics or motorized screw.
In this design, we tried to focus on making the chair adjustable so it can grow with her as needed. We used motorized wheels controlled by a joystick in one of the arm rests so she can move around independently with a box-like area under the seat to hold the battery and receiver. We made the headrest, the arm rests, the back of the seat, and the footrest adjustable to different heights. We also added a seatbelt to keep her secure.
In this design, we decided to use a detachable car seat for the chair for easier collapsibility. We still have the motorized wheels, the joystick, and the place for the battery and receiver. We also added a scissor lift with a motorized screw so that the chair is easy to lift and lower to different heights. We also changed the front wheels to swivel wheels to make turning easier.
This design differs from the previous two in that the lift mechanism utilizes a parallel linkage design with screw type motorized linear actuator. The arrangement is similar to double wishbone suspension with the chair taking the place of the hub and the linear actuator taking the place of the shock. This design also includes a motorized rear wheel drive train with controls located on the armrest. The seat is adjustable to hold her comfortably and securely.
We selected concept design 2 to feature the scissor lift design for the height adjustment; however, we are taking elements from design 1 and 3 to incorporate into the design. We are replacing the car seat with a modified chair and taking all the adjustable parts from designs 1 and 3 so that Avonlea can grow with the chair.
Our design involves using a past chair that Avonlea had and modifying it by motorizing the wheels and the height adjustments. We are replacing the hydraulic cylinder with a linear actuator to make lowering and raising the height much easier for the family. We are also buying a driver kit to motorize the whole chair that will be controlled by a joystick. Since Avonlea has grown, we will be replacing her old chair parts with new cushions that are adjusted to her size now and add a headrest since her old chair had no support for her head. With the motor modifications, we need to replace the front and back wheels and their mounts with parts we design and will manufacture using. We also will manufacture new mounts for the linear actuator as well as the mount for the battery and all of the electronics.
For engineering analysis 1, we have calculated the maximum current draw of the system to 17.5 Amps. This is less than the manufacturer rated 20Amp continuous/60Amp max current output of our battery. This means that the battery should never see more current draw than it is rated to handle. The manufacturer rates the motor kit as being able to travel up to 25km with our selected battery, and, at <4Amps minimum current draw (at 4mph), that should result in up to approximately 5 hours of continuous run time. Assuming regular day to day operation patterns, this should be more than adequate in allowing the child to operate the chair all day on a single charge. In addition, each motor can produce up to 12 N-m of torque, plenty for a chair only rated to a load capacity of 70 lbs.
For engineering analysis 2, we calculated stress on the linear actuator mounts under load in both the fully-lowered and fully-raised positions. Deflections shown are exaggerated for visualization.
For engineering analysis 3, we developed a wiring diagram for all powered components of the chair. The motors, ESC, and joystick all come as a kit with plugs for battery connection and charging included. The kit is rated for 24v DC. The linear actuator is rated for 12v DC with a max current draw of 5 Amps. The motor ESC will be connected to the battery in parallel with the linear actuator circuit. Between the linear actuator switch and the battery, a 24v DC to 12v DC 10Amp step down transformer will be wired in series in order to provide the linear actuator with the required 12v DC.
