For the last few weeks, our class has been hard at work on our midterm projects, culminating in a variety of creative ideas and beautiful craftsmanship. Building off my 2D drawing mechanism from 507 mechanical movements, I started prototyping a physical model of the epicyclic train (http://507movements.com/mm_502.html).
The (Iterative) Process
With Mechanism 502, I used Gear Generator (geargenerator.com) to create two sets of gears, one with three spur gears and the other with two. The website exports the 2D files which can be opened in Adobe Illustrator as shown below. The file needs to be cleaned up a little, and I created a bar to keep the gears in line. In order to best assess the functionality of the design, I used the Epilog to laser cut the design and used 1/4″ dowels for the gear pins.
The end result was the epicyclic train pictured below. As a fascinating feature, the mechanism was always uniquely received by others in how they chose to operate it. One could keep any of the three gears spatially fixed and rotate the mechanism around it. The entire mechanism could be kept in one place with all gears moving. The choice of which set of gears to glue to each other factored into the overall motion. Inspired by geometric Islamic art, I looked into the option of utilizing the dual circular motion from the mechanism. As seen in the first picture below, two dots on the second and third gear show how the gears rotate off sync from the overall circular motion. With this in mind, I envisioned a mechanism that used two writing utensils to create an intricate circular pattern. Unfortunately, this idea was abandoned due to some perceived impracticality with the writing utensils interfering with gear mechanics.
Keeping in the vein of epicyclic trains, I came across the first mechanism shown below which houses two gears inside a larger gear (http://507movements.com/mm_505.html). The mechanism can operate with either the center gear stationary or the outer gear stationary (I would end up choosing the latter). In addition this form of the epicyclic train, I also found a mechanism that transforms the rotary motion from two gears into linear motion. Interestingly, the linear motion follows a varied pattern with each complete turn of the gears. With the potential to combine these two mechanisms, I was set to bring about a new design with an epicyclic train!
First, the variable alternative traverse from the spur gears was prototyped using plywood. The mechanism works surprisingly well as long as the center of the center beam is restricted within a linear channel. The gears were again rotated on 1/4″ dowels. Once this mechanism was confirmed, the biggest question was the layering of each mechanism against each other. If the third gear was going to act as the center gear of the epicyclic train, then the other two gears in the train would overlap with the first mechanism. Thus, the first two levels above the board were reserved for the first mechanism’s gears and the links associated with it. The third gear in series would then transfer motion from the first layer height up to the fourth layer height, where the epicyclic train would operate. The linear member shown in the train image above connecting to the two internal gears served as the plasma cut metal piece, suspending the motion of the gears on the fourth layer height. The piece was plasma cut, and then post-processed by filing it down and sand-blasting. The image below shows the process of plasma cutting. In the process, I learned about the kerf limitations of the plasma cutter which nullified my intention for using it to make the link pieces for the first mechanism, which have thin edges around the dowels. In addition, the kerf also made some of the internal dowel holes on the plasma cut piece smaller than intended, leading to movement around the gear dowels.
With all the pieces ready as pictured below, all pieces were laser cut using 1/4″ plywood and the final product was assembled. As part of assembly, 1/4″ dowels were used again and stoppers were used where appropriate with hot glue. The two gears in the linear mechanism are removable, sitting on the dowels. The outer gear for the epicyclic train sits on three pieces that raise it to the fourth level. The two internal gears for the mechanism are suspended to the plasma cut piece using stoppers and hot glue. The final product is driven using the bottom right gear in the image shown.
Lessons Learned
One of the biggest lessons learned was to value time management. I assumed the project would not be too complicated despite the complexity of moving parts. For such a scope, I should have accounted for more time and definitely iterated more in order to get a better result. There were definitely some kinks I would have liked to improve such as meshing of the central epicyclic train gear and the larger spur gear in the first mechanism. I think there were also plenty of potential areas to experiment with acrylic. Ultimately, I would have wanted to add a finish or paint coating to many of the pieces. In some areas, the dowels also would be better off if capped.
From the finished product, I learned the importance of detailed tolerances in making a complicated part succeed. The use of dowels also helped me fit them to allow for smooth operation. In bringing the two mechanisms together, I was able to creatively separate their planes of operation.
Cost Analysis
- Material: 1/4″ plywood, 2′ x 4′, $12.00 x2
- https://www.homedepot.com/p/Columbia-Forest-Products-1-4-in-x-2-ft-x-4-ft-PureBond-Red-Oak-Plywood-Project-Panel-Free-Custom-Cut-Available-1994/204311240
- Aluminum Sheet, 36″ x 36″, $21.98
- https://www.homedepot.com/p/M-D-Building-Products-36-in-x-36-in-Plain-Aluminum-Sheet-in-Silver-57000/100351161
- Work Time, 13.5 hours, $135
- Total Cost: $181
