Revolving Armature Engines

Froment Engine

The revolving armature engine was invented by Paul-Gustav Froment in 1844. The Froment engine was a simple and elegant design that differed from its contemporaries in having no reciprocating parts, the only moving part being the flywheel.

Model Froment Engine

The model was built from one of the range of fully machined kits produced by the Old Model Company of Chichester, England (kit OMC-3).

Foment Engine c1850 It is interesting to compare this model with the engine in the photograph to the left, the similarities are quite striking. The photograph illustrates a Froment style engine that was built in France around 1850.

Froment's engine was one of the first electrical machines to do real work and his motors were successfully used for industrial purposes. The Froment design also influenced the modern day Induction Motor.

The operation of the engine is very straightforward. Pulses of electric current are fed to a pair of electromagnets via interrupter contacts operated by a cam on the drive shaft. The magnet attracts the steel armatures mounted on the perimeter of the flywheel causing the wheel to rotate.

The construction of this model is described in a build diary.

Video clip of the Froment Engine running

4 Pulse Revolving Armature Engine

Following the invention of the revolving armature engine by Paul-Gustav Froment his original design was further developed by a number of engineers. Various configurations of the component parts were tried in order to produce a practical electric motor.

4-Pulse Revolving Armature Engine

This model is based on original designs of the 1840s and represents one of the more successful of these developments. In this engine the coils were arranged in a more horizontal plane and the flywheel has been reduced in size. Compared with the original, rather tall, Froment design the result was a more compact but equally functional engine.

The model was built from a kit manufactured by the Old Model Company of Chichester, England (kit OMC-4). When the engine is running the magnet is energised as each of the armatures mounted on the revolving flywheel approach it. There are four armatures so the flywheel receives four power pulses per revolution.

Video clip of the 4 Pulse Revolving Armature Engine running

Rotative Engine

In an effort to improve on the Froment motor, various configurations of parts were tried. In 1908 Two Engineers from Indianapolis, Harry Hawecotte and Henry Klausmann, arranged the armatures to be within a Rotor instead of being mounted on the flywheel. This meant that the armatures passed between the rods of the electromagnets thereby gaining even more efficiency. They also placed a second set of electromagnets on the opposite side of the rotor creating a more powerful engine.

Rotative Engine

The model is based on their designs and as the two pairs of magnets are energized at different points in the cycle the engine produces eight power pulses per rotation.

This is another model built from a kit manufactured by the Old Model Company of Chichester, England (kit OMC-5).

Tin Toy Engine

This unusual item came from a collection of old, pre 1939, German manufactured tinplate toys. Such toys were sold in Britain between the wars and were often called "Penny Toys", a reference to their cheap price.

Tin Toy Froment Engine

Clearly this little toy electric motor is based on the design of a Froment style revolving armature Engine. A wide range of tinplate accessories were produced at the time, designed to be driven by steam toys, and this little motor could have been used to drive one. Presumably, from a toy maker's point of view, the revolving armature engine has the advantage that its operation is far more visible than a conventional electric motor.

There are no maker's marks, the only markings are the labels saying "4 volt - 2 amp". This delightful toy was cheaply constructed from tinplate pressings and is not very robust, it is quite surprising that it has survived as long as it has.