We wanted to create a Geneva mechanism that could make the driven gear rotate 180° for every full rotation of the driving gear. After doing some research, we were able to find a Geneva Mechanism design that achieved our purposes.
The mechanism is called a Lantern-Pinion system where the driving gear (pinion) only has half of its teeth while the driven gear (lantern) has all of its "teeth" which are rods perpendicular to the lantern surface.
The sizing of the gear was based on how the length of the crank rocker arm would fit onto the lantern itself. This made the outer diameter of both gears to be about 5 inches. Also, after calculating the forces that the gears were expected to face (about 20 lbs...), the chosen size was analyzed and we found it could handle the stress.
In order to generate the gears, we used Gearotic Motion. The program features a built-in lantern-pinion generation system which allowed variations of the number of teeth, size, and design. Since the program was only a trial version, it did not allow the exporting of SolidWorks files of the gears. To work around this issue, we took a screen capture of the gear drawings (seen in Figure 1) and imported it as a sketch in SolidWorks. The image was scaled to fit our desired outer diameter of 5 inches. 3D models were then built based off of the sketches.
To prototype the gears, we considered using 3D-printing, wood working, water-jet cutting, and laser cutting. We attempted to first cut them from wood by hand since it was the most cost effective method; however, due to equipment problems in the wood shop, we decided to laser cut the gears from acrylic because we only had an acrylic sheet that fit the restrictions of the laser cutter. To use the laser cutter, the raw material must be 1/4" or less in thickness and must not have chlorine in its chemical makeup.The gears were cut at the Tech-Shop located in Round Rock, TX. As seen in figure #, the resulting gear was within the specified dimensions. Unfortunately, due to the brittleness of the material, it fractured quickly and when placed under stress. See Geneva Mechanism (Redesign & Second Implementation) for our next steps.
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| Figure 1. Sketch of Lantern-Pinion System in Gearotic Motion. |
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| Figure 2. 3D model of Lantern-Pinion System in Gearotic Motion |