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| NanoEngineer-1 Gallery: SRG-I Speed Reducer Gear |
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This is the SRG-Ia, a parallel-shaft speed reducer gear created by Mark Sims. As you can see, it includes four components: an input shaft, an output shaft and a pair of coupled bushings (front and back). The goal of the SRG-Ia was to create a simple speed reducer gear with as few atoms as possible. The smaller input gear and bushing may be recognizable to you. They are borrowed from Drexler's Small Bearing, which has had the shaft extended and another copy of the bearing attached to the end. The sulfur atoms on the perimeter of the small bearing shaft where transmuted to silicon, allowing for additional layers of atoms to be added to build up and create rows of steric teeth.  This cross section of the input and output gears clearly shows how it was done. Notice that while 6-fold symmetry was maintained in the input gear, the number of teeth was doubled from six to twelve. Like the input gear, the larger output gear is also a derivative of the small bearing. On the inside of the shaft, oxygen atoms were inserted between the inner most carbons to increase the radius. Unlike the input gear, the number of teeth did not double as layers of atoms were added. If you count the number of oxygen atoms (in red) and the number of teeth, they both equal 18.  This POV-Ray rendering shows the front and back bushings in Tubes display mode, allowing you to see the side of both gears normally obscured by the bushings. You can also make out the four sulfur atoms used to connect the two bushings. Notice that in the animated sequence below, these atoms do not move. This is because grounds were attached to them, anchoring them during the simulation.
This simulation illuminated a design issue with the output gear, which can be seen in the animation loop above. If you look carefully, you can see oxygen atoms on the inside edge of the gear popping out intermittenly. This is an indication that the oxygen atoms are compressed too tightly on the inside of the shaft. I had to address this problem somehow. I also made some mistakes in the simulation setup. I had intended to attach the motor to the input shaft, but I attached it to the output shaft instead. This is evident from the animation sequence: notice the input shaft rattling around in the bushing while the output shaft turns more smoothly. My choice of atoms to anchor wasn't well thought out, either. SRG-Ia (8/31/2005)  In this updated simulation of the SRG-Ia, the input gear has the rotary motor and is driving the output gear. The anchors have been strategically placed at locations that I anticipate will connect to the SiC casing (yet to be designed). Notice that the sulfur atoms coupling the two bushings that hold the gears are not anchored, a more realistic scenerio. It appears from this simulation that the large bushing needs to have a smaller radius. You can clearly see a gap between the output shaft and the bushing in the animiation, which isn't surprising since I didn't carefully analyze the atomic distances between the shaft and bushing that form the bearing. So my next task was to focus on refining the output gear. I needed to address two problems:
SRG-Ib (9/2/2005)
This is the SRG-IIb, which addresses the two problems I described above. I also included a silicon carbide (SiC) casing to house the gears, providing a complete assembly unit with 8,366 atoms. The new gear and bushing combination is much tighter, resulting in smooth rotation within the bushings. In the simulation sequence on the right, I chose to include only the gears and atoms from the bushings, as well as a few atoms that connect the bushings to the casing. This allowed the simulation to complete more quickly while still preserving the atoms that contribute to the primary function of the device.  In this new cross section of the gears, you can see how I reduced the number of oxygen atoms on the inside of the output gear shaft. This resulted in a slightly smaller shaft diameter, requiring further adjustments on the bushing.  In this POV-Ray rendering, you can clearly see the atoms with the black wireframe boxes that were grounded for the simulation, which are those atoms that connect to neighboring casing atoms (removed for the simulation). You can also make out the shaft of the rotary motor driving the input (pinion) gear in the simulation. SRG-Ic (9/4/2005)
This simulation of the SRG-Ic includes all atoms, even those in the new casing. The SRG-Ic differs from the SRG-Ib only in the casing structure. I pruned atoms from the edges of the Ib that I felt were unnecessary. This reduced the atom count from 8,366 to 7,704. On the left, the casing has been displayed in Tubes mode while the gears have been left in CPK mode. This combination allows all atoms in the casing to be displayed without obsuring the dynamics of the gears. In the POV-Ray animation on the right, I've removed the top half of the front casing to expose the gears. - Mark |
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