Trapped Roller Clutch
Entry ID #: 2457
Created: Tue, Jan 12, 2016 10:45 PM
We have created The Trapped Roller Clutch for use in VEX Robotics. Currently in VEX, there is a product called the Winch and Pulley Kit. The Winch and Pulley kit is bundled with a ratchet. The main problem with the ratchet is that it was never designed for applications it is now being used for. There is too much friction when used in high RPM conditions and high torque applications and it is also very bulky.
Our team designed the trapped roller clutch because it is a significant improvement to the ratchet set currently sold by VEX. The Trapped Roller Clutch is easier to work with because it is compatible with both high strength shafts and regular shafts, it’s fully enclosed and it can be driven by any vex gear or straight by a shaft. The trapped roller clutch surpasses the VEX ratchet in many if not all aspects. For example, the trapped roller clutch is capable of high speed, high torque, has a very minute amount of friction. The trapped roller clutch is highly reliable and there is no audible click when spinning at high rpm's as it can get very annoying.
Application In Robot Design
There are numerous applications for trapped roller clutches. In our example, we have mounted the clutch onto a flywheel. The trapped roller clutch works by transferring power in one direction, but not the other. The trapped roller clutch is able to do this because, in the internals of the clutch, the inner hub holds three small rollers, on springs. When the trapped roller clutch spins in one direction, the geometry makes the rollers make contact with the outer gear, causing the entire clutch system to rotate. When spun in the opposing direction, the geometry of the clutch causes the rollers freewheel, causing the axle to just free spin. This design is perfect for use in our robots flywheels. As the motor powers up, spring force causes the rollers to make contact with the outer surface, causing the clutch to spin up the flywheel to the desired RPM. Once the motor stops spinning the axle, the geometry of the ramps on the inner hub will allow freewheeling, causing the flywheel to freespin. One of the major advantages of this part is to allow the control of 2 independent mechanisms from one motor. In our example spinning in the opposite direction of the flywheel causes the gear to turn, this can be used to control an entirely different mechanism!
Conceptualizing The Design
Our team used Autodesk Inventor 2015 to create this part.
First we decided on an outer gear size that is just the right size so that we could create an outer hub based on a pre-existing vex gear (in this case 60 tooth)
- Extruded 60 teeth with vex pitch and a flat surface of a rounded out gear
2. Extruded roller surface with keyslot for correct mate with outer surface
3. Created Inner Hub
4. Created the rollers
5. Assembled all components
6. Created case
7. Added Screws
Our team learnt many new things while working on this project. With our knowledge of CAD, our students are able to apply what they learnt in Inventor, with robotics and apply it into the workplace. For this reason, we will continue to use Inventor and other 3D Cad software as we get older. 3D printing is the future, it will replace the need for large manufacturing industries using old processes when parts can be custom designed and printed within hours. This is the main reason we would use Autodesk Inventor in the future, to use our understanding of Autodesk Inventor, design and create 3D printed parts to solve a wide variety of problems to be faced at home and in the workplace. Autodesk Inventor helps our team do a numerous amount of tasks. Such as calculate the amount of parts required to build a certain robot, calculate the total mass of the robot ( allows us to detect if the mass of the robot is causing the drive to stall), run structural analysis on certain components of the robot to see where the parts of the robot that aren't structurally sound. These are some of the few examples of Inventor usage in our team. One of the most important aspects we have learned is that designing a part or a mechanism in CAD is very helpful as it will help you build and assemble the part in software, which will potentially find flaws in the design before construction. The ability to visualize in Inventor, the robot you are designing before you construct it can be very beneficial in meeting time constraints and has been a great help for us over the past year.