The Electromagnetic Engine.

Updated: 3 April 2005
Magrini, Depoele added
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In the very earliest days of electric motors, it was far from clear that a rotary format was the best solution, and many scientists and inventors took their inspiration from horizontal steam engines. It is clear now that they were on the wrong track, as it is equally clear that for steam engines, a rotary system was not the way to go. See Rotary Steam Engines.

This page is dedicated solely to electric engines that convert reciprocating to rotary motion by a crank or equivalent. There were many, although the reciprocating electric engine proved to be the deadest of technological dead ends. Only a small sample are shown here.

Most electric engines were essentially solenoids that pulled a piece of iron into their centre when energised. This was coupled by a connecting rod to a crank and flywheel, just as in a steam engine. A set of contacts switched the solenoid current on and off at the appropriate times so the iron could be drawn out again by the flywheel and continous motion obtained.

The American scientist Joseph Henry (1797-1878) constructed a small electromagnetic engine, with a reciprocating beam. This is believed to be the world's first cyclic motor, ie one that continued working without manual switching or resetting. No image has so far been found. Joseph Henry did much work on electromagnetism and in 1893, his name was given to the standard electrical unit of inductance, the Henry.

In 1838 or 39, the German physicist Moritz Hermann Jacobi constructed the world's first electrically propelled boat, using a a reciprocating solenoidal electromagnetic engine of about 1 HP to drive two paddlewheels. It was publicly demonstrated it on the river Neva in Russia. Electric power came from a bank of chemical batteries, the fumes from which (probably nitrogen dioxide, but this detail is so far unclear) were so copious that the experiment had to be prematurely terminated.
However, Jacobi was back the next year with the same boat, but a better battery bank, a fifth the size of the previous one, and presumably less likely to poison its owner. The 28-foot boat managed an average speed of 3 mph while carrying 12 or 13 passengers.

Luigi Magrini (1802-1868) was born in Udine, and obtained a degree in mathematics from the University of Padua in 1825. He held the chair of Physics at Florence, Italy, and worked with Leopoldo Nobili, the thermopile experimenter. See here for more on thermopiles

His reciprocating electric engine is in the Museum of The History of Science at Florence. Unfortunately photography is not permitted in the museum, so I am unable to show you the picture below.

Above: The Magrini reciprocating electric engine: circa 1840.

Note that the cranks are set at 90 degrees to avoid dead-centre problems- the engine was clearly designed to be self-starting. The switching system was a commutator on the crankshaft, not visible here.

Guiseppi Domenico Botto (1791-1865) was Professor of the University of Turin. His electric engine used swinging coils. There were 14 glass compartments in the wooden base that held chemical cells. Switching was done with mercury contact cups.
The Botto engine example in the Museum of The History of Science at Florence is labelled as "circa 1840" and "after Botto" which presumably means it was built by somebody else.

Unfortunately I do not have a picture of it; you can see the corner of its wooden frame on the extreme right of the picture of the Magrini engine above.


Charles Grafton Page of the USA was an early pioneer, and very clearly took his inspiration from horizontal steam engines.

Above: The Page reciprocating electric engine: 1844. Not a very expert drawing, unfortunately.

The Naming Of Parts:

Electrical input terminals
Yokes joining armatures to guide rods

This is the early form of the Page electromagnetic engine. Two solenoids are placed in tandem to drive the flywheel through a conventional crank, alternately pulling in two cylindrical armatures, and working on both directions of movement in the same fashion as a double-acting steam engine.
The current through the solenoids was apparently switched by a commutator on the crankshaft, though this detail is not very clear in the drawing.

Page later, in 1851, built an electromagnetic engine that developed 16 horsepower; this reached 19 mph when used in a battery-powered electric locomotive on the Baltimore and Ohio railroad. it is not confirmed that this was of the reciprocating type.


Left: The patent drawing of the Depoele engine.

This patent is dated 1891, by which time it was very clear that electric motors should be rotary. Nonetheless, Charles J Van Depoele of Massachusetts thought it was worth taking out this patent.

He was almost certainly wrong.

Solenoid reciprocating engines are example of variable-reluctance electric motors. Reluctance is a measure of how hard it is for a given electromagnetic induction to set up a circuit of magnetic flux- a kind of Ohm's Law of magnetism. If a magnetic system has moving parts these naturally take up a position that results in the greatest magnetic flux, ie a position of minimum reluctance.

The familiar rotary electric motor is usually a constant-reluctance design.

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