The electric motor in all Scalextric cars produced to date uses a
3 pole wire wound armature and a permanent magnetic field. Over the
years 3 general types of magnet has been used, in the 1960 a ferrous
(Iron based) block magnet was used then from the 1970s two shaped
magnets have been used. More recently some high performance motors
have been produced using the stronger shaped neodymium magnet.
This article relates to the earlier ferrous block magnet as fitted
to the RX
Hurricane, and the Formula
How a motor works
A motor works by having two magnetic fields attract / repel one another,
just like two block magnets do. In a motor one magnetic field comes
from the ferrous block magnet and one from the electrical current
flowing in the wire windings. Therefore the stronger the magnetic
field from the ferrous block magnet the more torque the motor will
produce. The electric current is switched from winding to winding
by the commutator as the armature rotates.
In any non magnetic ferrous material the spins of the electrons in
the atoms of the material are randomised giving equal numbers of "up
spin" and "down spin". It's the spin of the electrons
that create the magnetic field. When the ferrous material is placed
in a strong magnetic field the electrons all align so they spin in
the same direction producing an overall magnetic field. The material
has become magnetised.
However, the magnetised material is in a higher state of energy
compared to non magnetic material. This means a ferrous block magnet
will lose its magnetic effect when it can. To maintain the magnetic
effect of a ferrous block magnet the magnet must be kept in a tight
magnetic loop. This is why magnets when not being used use a "keeper".
A "keeper" is a piece of magnetically conductive material that keeps
the magnetic field in a fixed ferrous loop.
Magnets in motors
In a Scalextric motor the ferrous block magnet is kept in a tight
magnetic loop using the steel motor frames and the ferrous core
of the armature. In this way an assembled motor will retain its
magnetism for many, many years. Each of the Scalextric motors that
use the ferrous block magnet are magnetised as an assembled motor.
The problem with the Scalextric motors that use a ferrous block magnet
is that if the magnet is removed from the motor, for any reason, it
will immediately lose some of its magnetic field strength. Basic tests
show that the magnet will be 20 to 30 percent weaker. There is no
gain in magnetic field strength when the magnet is refitted to the
motor. Do this enough times and the magnetic field will diminish to
the point where the motor will not operate.
To maintain a healthy magnetic field strength the ferrous block magnet
must be magnetised with the motor assembled. Specialists,
like Scalextric Car Restorations, have the equipment to do this. Completely
"dead" magnets can be brought back to life and the magnetic field
can even be reversed in just a second. Reversing the magnetic field
will change the direction of rotation of the motor.