Magnets in Scalextric motors

Keeping the Scalextric motors at their best by keeping the magnet strong

Introduction

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 motor, Powersledge motor and the Formula Junior motor.

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.

Magnetism

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.

Conclusion

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.