Robotics Education & Competition Foundation
Online Challenges

38211A's Planetary Transmission Gearbox


Entry ID #: 6417
Created: Tue, Jan 15, 2019 8:20 AM

Introduction This years’ game, Vex Turning Point, is the first year for V5 system to be put through its paces. In a competition where speed and power is key, high drivetrain power is key to success at every competition. Our team has observed that V5 drivetrains have an overwhelming amount of both speed and torque compared to equivalent 393 drivetrains, and we have searched for a means of combating this lack, for we only have access to Cortex hardware. Enter transmission gearboxes, which allow for both high speed and high torque, the qualities we were looking for. While most transmission designs require the use of pneumatic pistons, the planetary transmission gearbox stands out in that it doesn’t require pneumatics. The best documented example found online was that from 7 years ago, part of team 4194B’s drivetrain for the robot they had brought to Worlds in 2012. The fatal flaw of this design was the chain - used in place of an actual ring gear - which would start skipping when too much torque was applied, effectively rendering the torque setting of the transmission useless. By creating a custom planetary transmission gearbox, this allows us to overcome our lack of V5 System hardware and face head-to-head with V5 robots in future competitions, competing for both game pieces and Platforms during the endgame. Description This new planetary transmission gearbox would be used in place of a standard gearbox for the drivetrain of a robot. The gearbox was designed to use pre-existing Vex hardware, but also to take up a minimal amount of space, important when fitting as many mechanisms as you would need for this competition. The gearbox has 3 shaft holes; 2 for input, and 1 for output. The gearbox also has multiple different sets of holes to make motor orientation flexible (up to 12 different possible orientation combinations), which was also an important consideration when designing a drivetrain. The 2 input shafts would go into motors, and the output shaft would ideally be mounted to the drivetrain. Along the output side of the gearbox housing is a line of holes, all spaced ½” apart so it would correctly align with the Vex EDR C-Channel, allowing for easy and flexible mounting options onto any Vex EDR Structure. The gearbox, with its two motors, could then be programmed to spin to allow for torque and speed, which, thanks to the planetary gearbox design, can be set to an infinite number of different speeds, depending on each motor’s rotation direction and speed. Usage of Inventor For this project, I used Autodesk Inventor Professional 2019 64-Bit Edition Build: 136. Inventor was used first to lay out the already pre-existing Vex Hardware in a manner that would be usable and space efficient, making good use of the Free-Spinning Inserts to minimise friction, and Square Inserts to insure a solid hold on axles. Then, it was used to create new components, the two most important being the Planet Gear Carrier and the Ring Gear. The Planet Gear Carrier was essential to keeping the Planet Gears aligned and meshed properly with the Sun and Ring Gears, and to do this, I used Dimension constraints and Circular Pattern Revolve functions. These two functions insured that I had aligned my parts correctly, and simplified the sketching process. For the Ring Gear, I used the Spur Gear Tool, and created an internal gear. Prior to doing so, I had experimented with the Spur Gear Tool to examine what pitch, pressure angle, diameter, etc. would correspond to Vex EDR gearing, and created my Ring Gear based off these experimental values. To create the protective casing to house the gearbox as well as to mount motors to the gearbox and gearbox to a chassis, I measured out ample clearance around each of the rotating members of the gearbox, and sketched a plate out for all members to be situated on. From here, the outer perimeter was offset and extruded to create the walls of the structure, and the same process was repeated for the 5 screw posts. Conclusion Through the course of this project, I have learned the basics of using Autodesk Inventor to create a finished product. In doing so, I have learned about making constraints, using tolerances, and creating a product to be compatible with pre-existing hardware. I have also learned how to assemble robots in Inventor, how to make components move and drive to demonstrate actions, and what goes into designing a component for the competition scene. Having utilised 3D design software for the better part of the last 2 years, it is likely that I will continue to do so in the future. If I am to further explore the applications and benefits 3D design software, it will very likely be for engineering projects, as I am active in creating objects at home, mainly using a desktop FDM 3D printer. I would like to expand upon my knowledge of additive manufacturing, on top of mechanical engineering, to create durable and working mechanical parts. Autodesk Inventor would be a great asset to our robot prototyping and design stages, for it would allow for the robot to be virtually constructed without having to cut any metal, and without worry about running out of parts to use. This would also allow us to pre-plan all of robot construction ahead of time, so we would not have strange alignment and spacing issues later into the building process, and space can be used more efficiently. 3D design software will likely help me in my career path, and at the very least, be very relevant. I would like to go into an engineering career in the future, likely Mechanical Engineering, and with the advent of additive engineering being used in other sectors of engineering, such as space exploration, product manufacturing, and robotics engineering, knowing how to use a 3D design software will be invaluable. 3D design software would be useful in rapid prototyping, development, and fabrication of parts, especially with the recent development of finer resolution 3D printing technologies.