A flywheel is a mechanical device specifically designed to efficiently store rotational energy. Flywheels resist changes in the speed of rotation due to their moment of inertia. The amount of energy stored in a flywheel is proportional to the square of its speed of rotation. The way to change the energy stored in a flywheel is to increase or decrease its speed of rotation by applying a pair aligned with its axis of symmetry.
Common uses of a flyer include:
• Smooth the output power of a power source. For example, flywheels are used in reciprocating engines because the active torque of the individual pistons is intermittent.
• Energy storage systems Steering wheel energy storage
• Provide power at speeds greater than the capacity of a power source. This is achieved by collecting energy in a flywheel over time and then releasing it rapidly at speeds that exceed the capabilities of the energy source.
• Control of the orientation of a mechanical system, gyroscope and reaction wheel.
Flywheels are typically made of steel and turn on conventional bearings; these are usually limited to a maximum revolution speed of a few thousand RPM. High energy density flywheels can be made from carbon fiber composites and use magnetic bearings, allowing them to rotate at speeds up to 60,000 RPM (1 kHz). Carbon composite steering wheel batteries have recently been manufactured and are proving to be viable in real-world testing on conventional cars. In addition, its disposal is greener than traditional lithium-ion batteries.
Flywheels are often used to provide continuous power output in systems where the power source is not continuous. For example, a flywheel is used to smooth the rapid fluctuations of the angular velocity of the crankshaft in an alternate engine. In this case, a crankshaft flywheel stores energy when a torque is exerted on it by a firing piston, and returns it to the piston to compress a fresh load of air and fuel. Another example is the friction motor that drives devices such as toy cars. In stress-free and low-cost cases, most of the mass of the wheel is to the edge of the wheel to save on cost. Pushing the mass off the axis of rotation increases the rotational inertia for a given mass.
A flywheel can also be used to supply intermittent pulses of power at power levels that exceed the capabilities of its power source. This is achieved by accumulating energy in the flywheel over a period of time, at a rate that is compatible with the energy source, and then releasing energy at a much higher rate for a relatively short time when necessary. For example, flywheels are used in power hammers and riveting machines.
Flyers can be used to control the direction and oppose unwanted movements, see gyroscope. In this context, flyers have a wide range of applications from gyroscopes for instrumentation to vessel stability and satellite stabilization (reaction wheel), to maintain a spinning toy (friction motor), to stabilize magnetically levitated objects (Spin- stabilized magnetic levitation).