2.3 - Design Process
Initial Design Ideas
We set out to find a 4-bar mechanism with 1 degree of freedom (DOF) that could create a figure-8 path with an input link that could make a continuous revolution. We wanted this specifically so that the mechanism could be powered by a singular motor and run continuously, as our goal is to stir a pot continuously.
Initially, we used MotionGen to create different 4-bar mechanism configurations that would produce the desired figure-8 path.
Below are a few of the iterations that we tried:
After continued trial and error and some research, we found the design of an inverted parallelogram that would create a perfectly symmetrical figure-8 path about the center point of the mechanism. Additionally, if a spoon were put at the center of the link 3, then the face of the spoon will rotate as well. This additional rotation would allow for more effective stirring.
Unfortunately, after some prototyping and iterating upon the inverted parallelogram design, we found a significant oversight. The presence of toggle points that would interfere with consistent performance of the desired path profile. Therefore, we needed to pivot and start back at square 1 and create a different mechanism design.
After more rigorous research and trial and error, we finalized our design to be a 4-bar linkage system with a ternary link as link 3 that would carve out the desired path at the tip of the triangle, where the spoon would be placed. Although the figure-8 was not symmetrical and not in the center of the mechanism, we were able to adjust its position during the final integration to achieve our goal.
Prototypes and Iterations
In order to confirm the lengths and measurements of the inverted parallelogram design, we first created a cardboard and pushpin protype. Although it was not completely functional, it allowed us to confirm the lengths of each link before we fabricated a more robust prototype.
Next, we laser cut a wooden prototype to test the motion and path profile that we desired. The path we wanted was being generated, but we were running into a few issues with friction between links and some discontinuous motion that we attributed just to the friction and the fact that we used nuts and bolts instead of bearings. (It would be later proven that our design was the issue and not the material)
Next, we laser cut an acrylic prototype with a slot cut out to house a spoon in order to keep the main goal of stirring a pot in mind (Figure 7). This prototype alleviated the friction issue that we were running into earlier with the wooden prototype, but there was still an issue with the mechanism locking up and reverting the path to a half circle rather than a figure-8 at certain points in the motion. Despite making a smaller spoon and correctly orienting the acrylic prototype (Figure 8), we still ran into this issue. We finally determined to redesign our mechanism as a whole to avoid this issue.
Final Prototype
For our final prototype, we did not have much time in between pivoting from the initial inverted parallelogram design to the new ternary link design. Therefore, our only prototype of the final design was the final prototype we used on demo day. Our intent was to have the mechanism placed over the top of the pot and stir in the pot itself. To achieve this, we needed a base plate that would support the 4-bar mechanism, as well as house the electronics out of sight. We utilized a series of metal rods, shaft collars, bearings, and laser-cut acrylic and wood to create the mechanics of our final prototype seen below. For aesthetics, our Teaching Assistant Connor suggested that we try to make a theme for our mechanism to reflect. We chose to recreate a pond setting with a frog (4-bar mechanism) chasing a fish (spoon) that is swimming in the pond (pot) in a figure-8 path.