Design Rationale

Our goal for this device was that it be durable, robust, and easily repairable. The device is now on Lisa's wheelchair and maintained by Don Fredette at the Boston Home. We chose these goals based on our previous prototypes and Lisa's requirements.

First, we prioritized durability because Lisa's old mount would break or come loose often due to her frequent collisions. Our first prototype using a servo motor was a proof of concept and would not withstand long-term use. Our second prototype with a DC motor was more durable than the first; however, some of the components (e.g. the limit switch and the torque transfer mechanism) were still fragile. Therefore, we aimed to create a final device more durable than Lisa's old mount and our previous prototypes.

Left: our first prototype mounted onto Lisa's wheelchair. Right: the first prototype with labeled components

Our second prototype, which consisted of the same motor as our final device, a limit switch, and components housed in a cardboard box

Second, we wanted to ensure that the device was robust. Every time Lisa pushed the button, we wanted the arm to move consistently and to the same place without interfering with Lisa's other actions. For instance, Lisa should be able to lean her wheelchair back without affecting the device. Because our previous prototypes were not durable, they were also not robust: after multiple uses, the rotation mechanism would break and cause the device to stop functioning.

Finally, we wanted the device to be easily maintainable. It would be Don's responsibility to fix any issues once we mounted the device onto Lisa's wheelchair. Our previous prototypes were difficult for a person outside the team to maintain because the components were disorganized. For instance, there were too many unlabeled wires. Consequently, we took design decisions to make the device more compact and maintainable.