Linear Eddy current Motor FAQ
What are their advantages with respect to LIM's?
Owing to the presence of flywheels to accumulate mechanical energy, LEM has no peaks
of power consumption when launching: the power consumption may be made absolutely flat, when appropriate.
What are their advantages with respect to mechanical launchers?
As there is no contact between the car and the launching disks, there are no shocks nor friction,
with all the associated maintenance; also passenger's experience, though still thrilling, is with a soft acceleration.
Other advantages?
If the launched vehicle may return back in case of accident, the LEM will simply stop it safely,
without requiring more equipment or other safety devices. Notice also the very simple, hence reliable, mechanical setup.
What are their disadvantages?
Like eddy current clutches and drives, that are based on the same principle as LEM,
the efficiency is relatively low, due to the difference in speed between the driving disk and the conducted car.
What are they made of?
A LEM is formed by a stack of rotating disk units, that may be all identical, only similar
or different in their dimensions (but also a single disk unit may work of course). Each disk unit contains an
electrically conductor disk and an electric motor spinning about the same axis. A flywheel is also mounted on the same
axis to flat out power consumption. The disk units are supported under the track and the conducted cars carry
a magnet assembly, just of the same technology as used in Megamag brakes
How are they big?
The number of disk units, their dimensions and the power of the electric motors
is calculated for each installation. To give an example, a car weighing 4000 lbs may be launched at a speed of 60 ft/sec
with an acceleration of 1.6g by a stack of 45 disk units; each unit comprises a flywheel weighing 200 lbs, a disk 16" in diameter
and a standard electric motor with a power between 1.1 and 2.2 kW and turning between 1500 and 3000 rpm
(only motor's power and speed varies from disk to disk); the total
power consumption will be of the order of 60 kW for launching a car every 30 seconds. Of course less demanding applications
may require less disk units and other dimensions for the disk, the flywheels and the motors.
How do they work?
When the peripheral speed of the spinning disk is sufficiently higher than the linear
speed of the car during the launch, the eddy currents generated in the disk, by an interaction that is just the
same as explained for MegaMag brakes, will push forward the car. The combined action of many stacked disk units
allows to reach virtually any speed. Notice that the inverse is also true: if the disk spins slower than the car
or even in the reverse direction, a braking action is generated (see above about accidental returns).
How is the car or train speed adjusted?
Each motor in the disk units is controlled by a VFD inverter that allows it to spin at
different speeds: during the initial setup, each motor's speed is adjusted, based on detailed calculations, in order
to contribute for its best to the goal of the ensemble, and also to optimize the efficiency and the flatness of
the power consumption.
How are they maintained?
Mechanical maintenance is just as simple as mechanically simple are the disk units.
We also supervise online the behaviour of the LEM, in order to correct any unwanted shift in functional parameters.
