Epicyclic Gearing Kit
Entry ID #: 7042
Created: Tue, Jan 7, 2020 1:44 AM
Why did we choose to design this? In the Vex Robotics EDR part line, there is a vast array of parts that students can use to learn about the fundamentals of mechanical design. There is however, a gap in the library of competition legal parts that has yet to be filled: Ring gears. We designed our set of 3 ring gears, and accompanying carriers, to fill this gap,and to offer a cornucopia of new possibilities for builders and designers alike. Ring gears are a very important part of the engineering world in epicyclic gear sets, with uses spanning from pencil sharpeners to automatic car transmissions, and are even used in the V5 smart motor gearing cartridges. Epicyclic gear trains also have benefits over spur gear trains. Among these benefits are: Load is distributed across multiple teeth, very compact size, and a reduced risk of skipping under high loads. How and where would these parts be used? These parts would mainly be used for high gear reduction in compact spacing in mechanisms such as transmissions or on a lift. Due to the many modes of that these gears can be arranged in, there are endless possibilities for the usage of these gears. We are not allowed to use our 3D printed parts on a competition robot as we compete at the high school level, but if we could, we would use it on our lift. Our team uses a compound reduction of 1:7 driven and 3:5 driven, which takes up a sizable amount of space on the rear of our robot. With epicyclic gears, we could create a very compact gear reduction that exists on a single axis that could provide us with very high torque. Another way that epicyclic gears could be used in robot construction would be in drivetrains. In past games such as Sack Attack and Turning point, a lot of torque was required. A transmission could be constructed in such a manner to switch between different modes such as high speed low torque and low speed high torque. How did we design these parts? Our team designed these parts with 3 main goals in mind: the parts must be simple to expand the usefulness of other currently available parts to have a similar style to the "high strength" line of 1/2 inch gears To accomplish this, we used Autodesk Inventor. We started off by designing the ring gears. We imported the CAD models of the 36, 60, and 84 tooth gears into Inventor. We then exported the profiles of the gear teeth into a .dwg and then pasted that into a sketch. We rotated them to align them with the x axis, as the drawings had a 2° or so tilt. Once we had all of our outlines aligned, we created a 4th gear profile, with 108 teeth by using the Circular symmetry tool. Then we put them into 3 new sketches, with inner/outer tooth counts of: 36/60 teeth 60/84 teeth 84/108 teeth We then extruded all of these by ½ an inch to match the thickness of high strength gears. After that we added mounting holes with radii of 0.09” for 8/32 screws. We then added additional geometry that was extruded by 1/16” down on both faces to create ribbing and to save weight on each part. Finally, we used the fillet tool to add fillets with radii of 0.03” to fit into the style of the high strength gears. Once we had completed the models of the ring gears, we moved on to creating the 3 carrier gears. We used the same profiles of the 36, 60, and 84 tooth gears as we had with the ring gears, and started by extruding them to ¼”. We then added a ¼”x¼” square hole in the middle of the face so that the piece would be compatible with ¼” high strength shafts and 1⁄8” shaft inserts. After that, we placed mounting holes spaced at regular intervals (60° for the inner 6, and 30° for the second row of 12 and 30° for the outer 12). We chose to do intervals of 60 and 30 because that allows for the placing of 3 gears around the center planet which is the least amount required for the gear to remain centered and aligned, and for standoffs to be used to connect with another carrier gear to keep all of the axles aligned. Then, we included geometry that was extruded down 1/16” on both faces to save weight. Finally, we used the fillet tool again and added fillets with radii of 0.03” to fit within our 3rd goal of design continuity. Conclusion: What did we learn? Throughout the process of creating these parts, we learned a lot about the use of design software and its usefulness for rapid prototyping. In the beginning of the design of our largest pieces, we faced issues with moving too many points around for the computer to handle. We learned how to get by this by copying an individual tooth, moving it, and then using the circular symmetry tool to remake the piece at the origin. This project has also helped our team understand the uses of CAD software. We have begun using it to plan out our robot more efficiently, which helps us not run into issues down the line in the physical construction of our robot. All 4 of our team members plan on entering STEM related fields, with 3 of us planning on going into engineering disciplines. In this rapidly developing field, the use of design software is a necessity.