Robotics Education & Competition Foundation
Inspiring students, one robot at a time.

Vex Transmission Clutch


Entry ID #: 2418
Created: Tue, Jan 12, 2016 9:41 PM

The part I created is a transmission clutch and is made up of three components, a high strength gear adapter insert, a sliding clutch collar, and a shifting lever. The purpose of these components is to allow for the changing of gear ratios in a compact and reliable way. Changing gear ratios allows a design to adapt the output rotational force from a motor to suit the situation. An application example would be a drive chassis, where a high speed gear would allow a robot to traverse a field quickly, and a low gear would allow for precise movements, and extra torque for pushing. Previously, transmissions in Vex had to be linear, where different gear ratios are stacked on two parallel shafts, and ratios are changed by forcing one axle forwards or backwards to mesh different sets of gears. This setup is large and hard to integrate into most mechanisms easily. In addition, without a clutch mechanism to engage or disengage gears, the forcing of different gear ratios to mesh often results in stripped or chipped gears. With the transmission clutch I made, the gears on the drive axle are able to spin freely while changing ratios or in a neutral state, preventing damage, and allowing gear ratios to be changed in a much smoother fashion. The assembly, which consists of three components, makes use of existing Vex components for optimal compatibility and easy integration. The first component is a high strength gear adapter insert, which replaces one of the free spinning inserts in a high-strength gear, allowing the gear to spin freely when the clutch collar is not engaged. The high strength gear adapter insert features four teeth along the outside which mate up with teeth on the inside of the clutch collar to engage the gear. The teeth are tapered and rounded to allow for easy and smooth engagement. The clutch collar slides along the drive axle and is anchored by a shaft collar at each end. It features teeth inside each end to mate up with the high strength inserts and engage shafts. The clutch collar is designed so that two gear adapter inserts at either end cannot be engaged at the same time, preventing damage, as well as allowing for a free-spinning neutral setting. The clutch collar is moved along shafts by the shift lever, a Vex shaft attachment that rests inside the clutch collar’s notch. When the shift lever is rotated, the clutch collar engages or disengages with the gears on either end. The end of the shift lever is rounded to enable smooth shifting and minimize rubbing and friction. To create my part, I used Autodesk Inventor, to create two dimensional sketches which were then adapted into a solid three dimensional form. For the gear adapter insert and clutch collar, I started by creating a sketch of the side profile of the component. I then revolved the sketch around a center point, creating a three dimensional body. Afterwards, I created sketches on the flat planes of the clutch collar and gear adapter insert, which I extruded into the holes for the Vex shafts to pass through. Lastly, I created sketches for the tapered engagement teeth on each, checking the clearances and tolerances with each part periodically, to ensure that everything fit together with no collisions or interference. For the shift lever, I created a sketch of the profile and then extruded it to its thickness. Afterwards, I filleted all of the edges with the same radius as many existing Vex components and set them to the same sea green hue so that the components looked finished and coherent with the rest of the Vex product line. In the course of this project, I learned about tolerances and improving strength. To ensure that my components work in a real life scenario, I examined other existing Vex components and measured them, noting the tolerances and clearances they needed for smooth operation. Similarly, I learned about material thicknesses by examining existing Vex gears and measuring their thicknesses to determine how small I could make my components without compromising strength or rigidity. I have used Autodesk Inventor for around a year, and will continue to use it for anything I need to design, as it has helped me design many projects, from garage shelves, to wheels to be 3D printed for a radio-controlled car. I enjoy using Inventor as it allows me to quickly realize my ideas accurately and intuitively. Knowledge of Inventor as part of a competitive robotics teams allows us to create specialized components that other teams do not have access to, providing a unique advantage. Learning 3D design software such as Inventor has helped me in high school, and I have no doubt it will help me with projects in college, where I plan to study mechanical engineering. Knowledge of 3D design software and familiarity with Autodesk programs will give me advantage in when I am seeking a job as an engineer.  

Links / Videos

Online viewer clutch collar

Online viewer shift lever

Online viewer high strength gear adapter