Design Alternatives and Options
Ratchet Mechanism
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This idea was modeled after using a bike gear to bring the leg up and down the body of the crutch. We found out it was actually very similar in concept to the final design of the linear actuator: what we envisioned is exactly what happens in the linear actuator.
Dropper Post
The dropper post was also bike inspired: a dropper post is an easily adjustable bike seat. It works as a mechanical switch set to your height for the bike which then locks easily. This was a much more expensive option, and wasn‘t fully adapted to our project.
Worm Wheel
A worm wheel works by using a gear a rotating frame or pole. While we played with this idea for a little, it was pragmatic to figure out how to rotate the frame of the crutch.
Linear Actuator
This is the option we chose in the end because it was the most efficient for both cost and utility. It uses a motor to extend and retract a pole. When selecting the linear actuator we finally used, we were constricted by budget and the needs of our project for weight, speed, and length. This was a big design choice, so we initially played around with one of Professor Godrick’s actuators before making our decision. Our linear actuator moves at a rate of 10 mm, extended 12 inches, and weighed about 2 lbs.
Design Process
Fail Early, Fail Often
Building with Each Iteration
Once we picked the linear actuator, our first step was making a model. We attached the linear actuator to PVC pipes to get the outline of the linear actuator and how it worked with the shape of the crutches. We found that the linear actuator could fit in place of the extension leg already on the crutch if it was secured by mounts at the top and bottom of the linear actuator.
Controlling the Actuator
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We iterated the most on how we were going to control the linear actuator. Initially, we were going to have two buttons per crutch: one that would go up and one that would go down on both of them: a total of 4 buttons. We modeled this with two buttons that could turn separate lights on and off.
CAD Iterations
Storing the Battery, Securing the Actuator Below the Handle, and Securing it at the Base of the Crutch
Control Box
The box went through all its iterations in CAD. We first had to decide on the orientation of the battery and circuit board inside, and how we wanted the wiring to go from the button and actuator to the circuit board inside. There were a lot of minute details added on as we realized that we had more needs that the box needed to satisfy. We went from one bigger compartment to placing a divider that separated the battery and the switch, and added some additional features to the inside of these compartments so that the circuit board and battery would fit snugly. We had a very limited space and specifically width and depth to work with.
Base Mount
We designed the base support first, and ran into an obstacle where if the base mount fit over the thicker base of the linear actuator, it wasn’t tight enough to the body of the actuator and the crutch. We solved this by designing a horseshoe clamp that wouldn’t have to slide on to the bigger base but instead would snap on, and then fit under the initial support.
Below the Handle Mount
The mount below the handle for the linear actuator wasn’t iterated upon as much, but came with it’s own challenges. It was extremely tricky to secure the linear actuator with a nail through the interior of mount, the linear actuator, and the frame of the crutches.
Continue to iterate
After we finished the project, we continued to iterate the final design. We spray painted the crutches and added additional arm pads to increase the comfort of the design. We also added measurements to the linear actuator so that the user can go straight to the height they want
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