Design Process - JG

The majority of my design process involved discovering a balance between my link lengths and functionality. It was crucial to my design that the input link was able to complete a 360° rotation to achieve the desired motion. I quickly found that just because a digital model could run smoothly, this didn’t mean a physical model would do the same. Digital tools such as PKMS don't take into account factors such as joint size and material, friction, or stresses between the links. Below we can see a PKMS model of the quick return:

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 I built several early models out of cardboard to help me test the tolerances of a physical build, then tested the link sizes in PKMS to discover an ideal quick return ratio. Below are 2 early prototypes, one that was fully functioning while the other was used for sizing estimates.

While this functioning prototype had the desired output motion, it was nowhere near smooth enough to pass for a final build. The links and joints were flimsy and inaccurate, and the grounding components were not stable enough to fully support the mechanism. However, it served as a great prototype to test different link lengths and orientations as the components were easy to move and manipulate.

After several iterations of physical and digital models, I settled on a set of working link lengths as seen below:

I found that with these lengths we will see an acceptable quick return that would be easily controlled in a hand-held mechanism. While the lengths could be altered to absolutely maximize my output velocity, I felt as though attempting to reach this maximum would make the mechanism difficult to control. I expected this to be a hand-held device, and thus needed to be able to be controlled and operated with only one hand supporting the ground. By designing for the mechanism to not operate at full efficiency, I was able to obtain a easy-to-maintain final product.