Robotics Education & Competition Foundation
Online Challenges

Low Friction Flywheel and Ratchet Design

2

MASTA WU
Entry ID #: 6274
Created: Mon, Jan 14, 2019 11:37 PM


    This part was created with the goal of producing an efficient flywheel design that will outperform all other competing flywheels, which decreases power draw, allocating more power to other systems on the robot. This low friction ratchet gear fabricated out of a VEX winch drum replaces the VEX ratchet gear from the winch and pulley kit for the flywheel on our robot. The disadvantage of using the VEX ratchet gear it has exceedingly more friction. The standard VEX ratchet gear acts like how a square shaft in a square hole stops spinning sooner compared to a round shaft spinning in a round hole. Reducing the number of steps in the racheting gear is like adding more sides to a square shaft and square hole until it is almost a circle. A conventional ratcheting flywheel using a VEX ratchet gear will experience a greater loss in mechanical energy thus the flywheel will stop spinning sooner. This is a major problem for our team due to the fact that we are still using Cortex based motors that have a PTC (Positive Temperature Coefficient) fuse that will quickly overheat and result in a "stalled" motor that will only run again at a slower pace after 9 seconds. With the custom low friction ratchet wheel, there will be less mechanical energy and angular momentum lost due to friction in the ratcheting system between the ratchet gear and pawl, keeping the wheel spinning at a higher tangential velocity for longer. This is important because less energy is required by the motors to spin up our flywheel to operating speeds, reducing the load the motors are subject to, thus dramatically reducing the amount of heat created, which in turn keeps the PTC's cool.       The mounting of our ratcheting system is also unique. Other ratcheting systems are mounted on a 86 tooth high strength gear, which is directly driven by a more powerful VEX v5 motor. When other teams let their flywheel free spin, multiple gears in their gear train spin, resulting in a loss of energy due to friction between the gears, the shafts and bearing surfaces and friction in an inefficient ratcheting system. When our flywheel free spins, only the 4in traction wheels spin because the ratchet is mounted directly on the free spinning wheel. The only sources of friction in our system is between the free spinning wheels and the shaft and the flywheel pawl ratcheting on the low friction ratchet gear. The byproduct of this low friction design is an efficient flywheel that will significantly outperform other flywheels in terms of efficiency.       Our team used Autodesk Inventor Professional 2018 when modeling the low friction ratcheting system. Inventor Professional 2018 offers a stress analysis program that helps determine how geometric variable impact our design. Our team simulated the amount of stress our low friction ratcheting gear will experience during maximum load to help us confirm that the ratcheting assembly will not fail in intense competition.       Our team learned that inventor is an important tool in order to stay competitive in the VEX competition. In the future, we will create our designs in Inventor in addition to drawing sketches. We will use inventor to do stress analysis on future structures such as lifts and drives on our robot in order to predict stability and reliability of that particular system. This will ultimately eliminate the step of physically building and testing structures, which is a major consumption of time and materials.

Links / Videos

This is a video of our low friction in action operating at 600 rpm.