Two Motor 1:1 Gearbox with Optical Shaft Encoder Mount
bossgivol
Entry ID #: 4453
Created: Tue, Jan 2, 2018 12:22 PM
Introduction Team YNOT created a 2-motor gearbox that incorporates an integrated quadrature (quad) encoder for use on Vex robots. The function of the gearbox is to decrease the amount of space needed to provide 2 motor power and sensing ability on a single wheel of the drive train. Design Explanation Our strategy in designing this year's robot required a drive train capable of both speed and strength. In order to maximize speed, we chose turbo motors. In order to maximize torque, we used a total of 6 motors on the drive. We also needed sensor that could give us exact rotations of the drive wheels in order to maximize our accuracy during autonomous programming. While creating our prototype on Autodesk Inventor 2017, we realized that adding 2 motors on each front wheel required 3 inches inside the drive train. This left no space for the quad. Placing the quad on the outside widened the frame by 2 inches. In this position, the quad would also be exposed to damage as the robot maneuvers during competition. Because VEX metal comes with holes drilled at a fixed distance apart, we were unable to position our motors and quad as compactly as desired. Ideally, our design would include a gear box that allowed 2 motors and the quad to be contained compactly on the inside of the drive train. We also wanted a sturdy design that could stand the ballistic movements that occur when the robot crosses over the scoring bars. We designed our own custom 2-motor gearbox so that the motors and quad could be placed in closer proximity to one another, allowing us to position all three components compactly on the inside of the drive train. This part improves our overall robot design by allowing us to utilize a more compact and protected motor/sensor configuration. Inventor Explanation Design: Using Autodesk Inventor 2017, sketch 1 was created by drawing a rectangle measuring 4.75in x 2.75in. Next, a circle was added near the middle for the drive shaft. Using construction lines, a line was drawn the exact distance needed to allow two 36 tooth gears to mesh properly. This measurement represents the minimum distance between motors. The gear holes were staggered vertically, placing one motor right side up and the other upside down, in order to decrease the distance between them. Two screw holes were added vertically for each motor ( 0.5 inches apart -fixed distance). Using a construction line from the same starting point, a hole was created at the point that the 62- tooth gear meshed with the middle 36 tooth gear. The shaft which passes through this hole allows the quad encoder to be firmly and compactly incorporated with the motors. Using calipers, the distance from the quad shaft to the screw hole on the attachment bracket was measured and the hole that secures the quad to the gearbox was added. The next step involved transforming the 2D sketch into a 3D object. This is called extrusion. Using the extrusion function, the design was widened to 0.25 inches. The next sketch included construction circles that mimic the position of the gears. This allowed us to see where support structures could be added without interfering with the gears. Supports were then made using rectangles around the perimeter of the gearbox and extruded to 0.25inches. Sketch 3, the design from sketch 1 copied and extruded. This serves as the other side of the gearbox. Sketch 4, a rectangle was created around the center motor shaft measuring 2.75in x 0.875in. A phalange with four placement holes that allows us to attach the entire component inside the C channel of the drive train frame was added. Finally, using the Fill It tool, the corners of the gearbox were rounded. This gave the unit a cleaner and more sleek appearance. The diameter of the motor screw holes was also increased in order to improve accessibility. Production: The design was saved as both .stl and .ipt files and exported it. Cura was used to print the file on a Lulzbot Mini printer. We chose nylon (bridging) filament by Taulman for its increased mechanical durability compared to PLA. Implementation: After assembling the gearbox, it was quickly and easily attached to the drive train frame. We have been very satisfied with our design as it effectively solved the problem we faced concerning spacing on our drive. Conclusion As founder and chief engineer for our rookie VEX U team, I have enjoyed the freedom of designing, printing, and using my own custom parts this season. From my first simple bracket three years ago to the multitude of parts I have produced in VEX U, Autodesk has always been there helping me create whatever I can imagine. With each project, I learn more about the versatility and capabilities of this innovative Autodesk product. Starting college with a background in Autodesk Inventor has been an invaluable asset for my freshman engineering projects and has helped me gain recognition from my professors. I encourage all middle and high school teams to explore this limitless creative tool. I plan to continue to develop my skills with Autodesk products as I prepare for a career as a product design engineer. VEX robotics helped me discover my passion for creating new things and with Autodesk, I will continue to design products that will make a better world. Team YNOT of the University of Tennessee Knoxville
