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For the bucket, we knew it had to turn 180 degrees at the end of its path, then quickly reset to its starting position for the next sweep. We first found a complex 8-bar mechanism that would achieve a complex translation and rotation motion, but later simplified it to a simple 6-bar half-rotation motion with a quick return. This allowed us to cut fewer links, minimized our chance of error in joint motion, and minimized the space needed to offset each link. The overlapping motions can be seen running below simultaneously.
Once we had our desired motion for each mechanism on Linkage, we noted the ratios of the lengths of each link in the mechanism with respect to the length of the sweeping motion so we could scale it to any size we wanted. Our limiting factor was the size of our bearings, which were 22mm outer diameter and 8mm inner diameter. With this in mind, we knew the smallest link we could make was 36 mm in length from edge to edge, including a 5mm buffer for the wood to surround the bearings and axle holes.
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Our first working model delivered the exact motion we were looking for, but was a little tedious in the assembly. To ease the construction of the final prototype, we scaled our links up slightly so the smallest link was 40 mm in length and much more comfortable to handle. We .
Our next challenge was solving the issue of both mechanisms interfering with one another. The bucket needed to be still when the broom was sweeping to make sure the debris landed in the bucket, and the broom had to be positioned in the back as the bucket dumped its contents so it was prepared to sweep them back. To solve this problem, we designed a complex gear train to be concealed within the box. Our most important gear was the half-gear seen below. It was connected to a full gear of equal radius and pitch by securing them to the same axle. The full gear meshed with the input rotation so the half-gear would always be spinning, and the half-gear meshed with each output so only one motion would be engaged at any given moment.
In our prototype, we also discovered that wood worked very well with our bearings and axles, so we as well as producing smooth gears of our desired size. We decided to stick with plywood for the entire project . This also added because it was mechanically satisfactory while also adding to the mechanical art aspect of the piece, giving it a da Vinci-esque aesthetic. With TA permission, this inspired our decision to stick with a hand crank as our power source rather than a motor, just as they would have in the 15th century.