allanhurst:
Using the eddy currents in a conductor is a terribly inefficient way of creating an induced magnet.
The efficiency can be high if you use enough material - large industrial induction motors are
efficient. The cost of permanent magnets in ton quantities means large AC motors are all
induction types, steel is a lot cheaper that magnets. The time constant of the induced magnet
can be several seconds in a very large motor, meaning the energy is dissipated slowly compared
to the working power going through the device.
But yes, small induction motors are poor compared to good permanent magnet BLDCs
Most of the energy goes into heat. It's basis of eg magnetic braking systems on lorries/coaches.
Normal motors use segmented silicon iron or permanent magnet rotors and can acheive 95%+ efficiency.
Induction rotors are laminated silicon iron too, with copper or aluminium squirrel cage embedded,
the laminations are essential to good efficiency in any cored motor.
OK for fun, but there'd have to be jolly good reason to try and make a motor this way.
Allan
The reason is the rail can be cheap as it doesn't need magnets.