The goal of the project was to create a gearbox assembly for a pre-existing vehicle. The vehicle is 15 kg and has a 60/40 weight distribution for front/rear. The vehicle will compete in a top-speed event and a hill climb event. The gearbox is expected to maximize the angular speed of the motor and maximize output torque. In this phase, the gears and shafts were modified to be suitable for 3D printing, as previously they had been designed under the assumption that the shafts were made of AISI 4130 steel. A housing structure to locate and restrain the bearings and shafts was also designed. All 3D-printed parts were created from a filament made of melted ABS plastic. This report outlines the process that was used to design the gearbox as well as the technical specifications of the final design. It also provides recommendations for improving the design in the future.
The final gearbox design consists of a single-stage shifting gear mechanism that can achieve success in both events. A gear ratio of 1.87 for the hill climb event will result in an output torque of 3.74 Nm. When a shift occurs, the gear ratio will become 0.53 and result in an average speed of 0.83 m/s along the 3-meter track. The shifting mechanism presents a clear advantage to non-shifting gears since the gearset can be changed between both hill climb and speed.
The housing was designed to be 93 mm long, 60 mm wide, and 80 mm tall. 10 x 10 mm cutouts made at the top and bottom of both side panels assured that the gearbox could be securely mounted to the body of the RC car. The cuts were designed so that any feature was no less than 5 mm in thickness. 5 x 5 mm cuts were made on the front and back end of the side panels to be able to mount the front and back panels securely. Additionally, the front and back panels are identical, which can improve the ease of mass manufacturing the design. The housing is designed to easily insert four bushings with a 12.75 mm outer diameter. To secure the bushings in place, rather than simply relying on friction, a small shoulder was designed on the outer wall of the housing.
Furthermore, the gears were engineered to assure they could withstand bending and contact fatigue failure. With pitch diameters of 56 mm and 30 mm and a face width of 12 mm, the contact fatigue failure safety factor, and the bending fatigue failure safety factor for the gear and pinion in both events were all over 1.1. While the required face width was only 7 mm, increasing it to 12 mm assured that all safety factors remained above 1.
Shaft Design 1
Changes between iterations of the shaft throughout the project.
Shaft design in phase 4.
In conclusion, designing a gearbox is a challenge that considers a number of variables. Every part of the gearbox needs to be examined and optimized in order to assure peak performance, from torque and speed requirements to durability. Through this process, the team can rapidly and precisely build and revise gearbox designs with the use of sophisticated computer-aided design tools, enabling the creation of transmission systems that are more effective and efficient based on feedback and the iteration process between phases. Different designs and iterations were investigated during the gearbox design challenge to discover the best solution for the provider’s requirements and to perform at the best ability in the events. The design was validated, and all performance criteria were satisfied in the final phase, following this the design was 3D printed and ready for performance day. This design challenge highlights the importance of collaboration, creativity, and innovation in the engineering manufacturing industry.
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