A previous post reported on the acquisition of Beacon Power, formerly the largest flywheel player, after the company went bankrupt.
One of the technical hurdles faced by designers of these whirling rotational energy storage devices is that spinning masses have a natural “wobble.” Most flywheel designers have employed expensive bearings, magnets, and materials in attempts to minimize this wobble to better align the flywheel’s axis of rotation with the rotation of a generator.
Enter Velkess, a Silicon Valley developer of new flywheel technology, which has invented a self-stabilizing design. Velkess owns U.S. Patent Application Publication No. 2012/0096984, entitled “Flywheel system” (‘984 Application).
The ‘984 Application is directed to a flywheel system in which the wheel is suspended in a non-symmetric damped gimbal system (9) (a gimbal is a pivoted support that allows the rotation of an object about a single axis, commonly used in gyroscopes). The shaft of a motor/generator (20) is attached to a flexible coupling (13), which is also attached to a rigid shaft (14).
The rigid shaft (14) is attached at its other end to a super-circular bare filament flywheel rotor (16). The shaft (14) can transmit high levels of torque and will not suffer the destabilizing displacement common in traditional flywheels.
According to the ‘984 Application, the invention allows one axis of the gimbal to dampen the resonant frequencies in the other axis:
[T]he non-symmetric damped gimbal system 9 of embodiment 15 has two different resonant base frequencies established by the differing lengths of the pendulum that each axis 10 and 11 create. This allows one axis 10 or 11 of the non-symmetric gimbal 9 to damp the resonant frequencies in the other axis 10 or 11.
As explained nicely by Chris Nelder in a recent Scientfic American piece, this feature minimizes resonant disturbances and permits more control of the device:
The gimbal in the Velkess is asymmetrical, so the two axes of rotation—the flywheel axis as well as that of the rotor, which drives the brushless, inducting DC motor—are not on the same plane, and have different periods of frequency. This dampens the resonance effects that make traditional flywheels hard to control (a resonant disturbance in one of the planes can intensify until the device shatters). With the gimbal, resonance in one plane is translated into the other, which is nonresonant at the same frequency. Accordingly, only very loose engineering tolerances—about one sixteenth of an inch—are required to build the device.
According to Nelder, the Velkess flywheel has significant advantages over previous devices like those made by Beacon Power, including slower, longer discharge of stored energy, and scalability. More info on the Velkess technology can be found on the company’s technology page.