The Basics
The ocean is unpredictive and directly converting its motion into electricity may not be ideal for the storage units. Thus, we utilized means to smooth out the kinetic energy harvested. The following components, flywheel & clutch, are used for the purpose.
What is a Flywheel?
A flywheel is a heavy wheel that is attached to a rotating shaft with the purpose of storing kinetic energy and smoothing power delivery from one mechanical component to another [1]. Due to flywheels being heavy, they take a lot of force to start spinning. . However, once they start, they can spin for a long period of time due to angular momentum, therefore storing kinetic energy, like how a battery stores chemical energy [2]. Flywheels come in different diameters and weights, where heavier and larger flywheels, as well as flywheels that are able to spin faster, can store more energy.
Every flywheel has a specific inertia, based on its mass and how its distributed throughout the component. The moment of inertia of a flywheel is defined as the flywheel’s resistance to rotational changes [1]. For example, a flywheel with large diameter, spoked, but with a heavy rim would most likely have a higher moment of inertia compared to a flywheel that is smaller and solid [2].
To learn more about how to calculate moment of inertia and what that looks like in regards to flywheels specifically, click here!
And if you want another description of what a flywheel is and how it works, check out this video!
What is a Centrifugal Clutch?
A clutch is a mechanical device that acts almost like a switch, where it can engage and disengage with another mechanical part depending on its direction of motion [2].
Typically, clutches are used in cars to control the connection between the engine and the drive train, allowing for the engine to drive the vehicle when the driver puts the car in motion [3]. A clutch allows smooth engagement and lets the engine to constantly maintain fast rotation when the vehicle sits in idle.
For a smooth energy delivery, the flywheel in this project needs to maintain a 1-directional rotation state that has little fluctuation. Thus, it becomes imperative that our flywheel is selective in receiving the output motion from the gear train, which is constantly oscillating due to the ocean waves. A simple clutch can be used to mitigate oscillation and increase the flywheel’s kinetic energy storage efficiently.
Design Decisions
Due to the oscillating motion introduced by our gear train, it is imperative that our flywheel exclusively rotates in a singular direction. This ensures a consistent power transmission to the motor and subsequently to the Energy Storage System. To mitigate the oscillations of the flywheel, a clutch can be employed.
There are many different types of clutches that are used for many difference purposes. In our project, a centrifugal clutch is used, similar to that of the type that is used in chainsaws, in order to connect the transmission of energy coming from the gear train to the flywheel. In a concise video, one variant—the centrifugal clutch employed in chainsaws—is explored. This specific clutch type served as a key reference point for shaping our own clutch design since the centrifugal clutch operates solely based on input angular velocity.
A high angular velocity in the correct direction lets the clutch to engage with the flywheel to power the latter, while a low angular velocity or rotation in reverse do not trigger engagement. The clutch does not require any other external input, making it a great component for a system that is not constantly maintained and operated.
Shown below is a video demonstrating our prototype and how the clutch and flywheel interact. Watch how the white magnetic coupling gear in the top left oscillates in direction while the flywheel consistently moves in one direction, allowing for the motor to also only move in that same direction.
Future Experiments/Design Work
While the prototype design met the project’s functional requirements, future improvement can be made. A stronger clutch made with better material can support higher system speed, along with a heavier, better supported flywheel can reduce energy loss and mitigate the input oscillation even further.
References
[1] “Flywheel.” Britannica. [Online]. Available: https://www.britannica.com/technology/flywheel
[2] “How do flywheels work?” Explain That Stuff. [Online]. Available: https://www.explainthatstuff.com/flywheels.html
[3] “How Car Clutches Work.” HowStuffWorks. [Online]. Available: https://auto.howstuffworks.com/clutch.htm
