Metal Construction

 
Reciprocating-Motor

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  After the expended lorry of the year 2006 in 2007 a simple motormodel was built, which is realizable with relatively few parts.
The idea for that came from a publication with the title Der Page-Motor (editor: Deutsches Museum). In this publication among other things the working of the american physician and physicist Charles Grafton Page (1812-1868) is shown and his efforts to replace the steam power by the electromagnetism.


In the course of his investigations at the beginning of 1839 Page presented the construction specification and the drawing of a motor, which he called Reciprocating-Motor because of itīs oscillating armature.

Picture credits:
Dingler u. a. (Hrsg), Polytechnisches Journal Stuttgart 1839, 72. Bd. Taf. IV, Fig. 31.
Pageīs Reciprocating-Motor
Pageīs Reciprocating-Motor

The source of power at this motor are two U-shaped solenoids and two softiron armatures above them. Both armatures are coupled by a rocker and can be pulled down alternating by switching on and off the solenoids alternating. The herewith generated motion works onto a balance, whose other side by means of a connecting-rod and an excenter drives the flywheel. The reciprocal switching of the solenoids is realized by a commutator which is mounted on the same shaft.

The model of the motor
The model of the motor
The construction of the model mainly occured in accordance to the above figure watching the scale, but some modifications were unavoidable.
Because this motor should be a function model, moreover was set no great store by outwardnesses.

Since the classical metal system doesnīt include U-shaped solenoids, instead of these 4 Maerklin-solenoids were used and mounted onto a warp resistant holder. The solenoids are wired in this way, that in pairs each with a magnetic north pole and a magnetic south pole faces upwards.
The 4 Maerklin-solenoids
The 4 Maerklin-solenoids

The rocker
The rocker
The rocker was simplified constructed , because a suspension above the armatures under geometrical consideration seemed to be disadvantageous.
As magnetic poles screw heads are used, which are to adjust exactly above the solenoids.

The balance also is beared in a warp resistant holder and transmits the motion of the rocker onto the connecting-rod at a ratio of 1:2.
The balance
The balance

The excenter
The excenter
The connecting-rod works onto an excenter with adjustable stroke. On the same shaft also the 15cm-Maerklin-wheel is mounted as the flywheel.
The stroke of the excenter firstly was adjusted to 1/2 inch, which corresponds to a rocker stroke of 1/4 inch (6,35mm).

The commutator is composed of two isolated mounted soft bronze contacts, how they are used e. g. in EMC-Technique (Electromagnetic Compatibility) and of a rotating contact, which also is placed on the shaft.
The commutator
The commutator

Because an appreciable attraction only effects at a small gap between armatures and solenoids, it is sufficient to close the contact per couple for about 1/4 rotation.
A longer closing time only marginal increases the power of the engine and heats up the solenoids needless.

The rotating contact consists of a fogwheel, on which a quarter-circle-shaped wire is mounted. During rotation the wire alternately slides over the bronze contacts and closes the electrical circuits for about 90°.

After the unproblematic assembly occured the start of operation, but this appeared to be very difficult. Also after hours of adjustment it was not possible to keep the motor in operation with a passable power consumption; at times even it was mistrusted, that ever existed a fully functional exemplar of this engine. Given the current situation the construction was checked to make potential optimisations.


Since the electromagnetic force works only over a very short gap, a possibly short rocker stroke seems to make sence. Therefore the stroke was decreased from 6,35mm to 4mm, corresponding to an excenter stroke of now 8mm.
But with decreasing stroke the free space of all mechanical connections and bearings disturbes increasing. By using superposed and against one another displaced perforated stripes and fish plates all free spaces were minimized carefully.

Graphical one can show, that the geometry of the motor isnīt so symmetrical, how it seems to be at first sight.


he geometry of the 
Reciprocating-Motor
The geometry of the Reciprocating-Motor
Although e. g. between the points R and O.T. as well as L and U.T. in both cases is an angle of 90°, the corresponding strokes of the rocker are different. For that reason both sides of the rocker "pull" different, and this can be observed as a slightly unbalanced operation of the engine.

However this effect disappears with increasing length of the levers and in the present case it can be neglected.

Against that it is indispensable to adjust the switching points exact as possible and to lubricate all bearings with a drop of light oil.

One reason for the limited rotation speed of the motor is the inductance of the solenoids, which delays the for an exact switching necessary steep current rise. Solenoids with a thicker wire and less windings would be more advantageous, but these at a lower voltage would need a much higher current.

As an essential cause for the extremely low efficiency was recognized, that during generation of the strongest electromagnetic force between armatures and solenoids the excenter nearly stands in the dead centres and so the force can be transformed to torque only insufficient.
According to a calculation in the mentioned publication at one exemplar of this motor an efficiency of only about 3% was determined.

After an adequate revision now the motor at a supply voltage of 10V works satisfactorily.
The average power consumption comes to approx. 10W and this is just enough to keep the motor in operation.



Data of the Reciprocating-Motor:

Length:41cm
Width:15cm
Heigth:23,5cm
Weigth:1,5kg
Number of parts:Not yet counted

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