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Watermills and Windmills of Middlesex (Second Edition)


Mechanism of the wind generator built by the Rollason Wind Motor Company near Willesden Junction station (from the Engineer, 20th April 1893):

“The motor has been designed to produce motive power for electric lighting and other purposes. A complete electrical board is installed in a wooden building at the base of the motor, and the outward appearance of the plant is shown in Fig.1, which is taken from a photograph. The motor itself is supported upon a light structure built of angle and tee iron, provided with a roof to cover the working parts.

 In designing the motor special care has been taken to make it as stable as possible in order to avoid danger of collapse in case of storms. The portion which receives rotary motion from the pressure of the wind consists of five wooden vanes, each vane forming a segment of a tube of very large diameter, and fixed so that it presents its concave surface to the direction of the wind. Thee vanes are fixed top and bottom to a five-armed star which is keyed to a vertical shaft. A space is left between the inner edge of each vane and the shaft itself, in order to allow for escape of air, and so that the centre of pressure may be as far from the axis of rotation as possible. In the present case each one is 20ft high, and the chord of the arc of section is 7ft long, while from the inner edge of the vane to the centre of the axis is 7ft. Each vane thus exposes a surface of 140 square feet, and it is assumed that two vanes are in action at the same time, so that a surface of 280 square feet is exposed to the action of the wind. The vanes themselves are protected by a moveable shield which covers 180 degrees of the whole circumference, and this shield is caused to take up a suitable position by the directive action of the wind upon an arrow-shaped vane at the summit. Fig. 2 is a diagram showing the relative positions of the vanes and shield in plan. The wind acts upon vanes one and two and partially upon three, while the space between the shield A and vane 3 allows for the escape of the air. It is claimed that, therefore, about one-half of the motor is under pressure, and the other half in a calm. The vertical shaft which supports the moveable shield is independent of the shaft upon which the vanes are fixed. The whole of the bearings consist of rollers arranged similarly to those used in turntables, and the castings containing the rollers are bowl-shaped, and are filled with oil in order to diminish friction. The vertical shaft is connected by bevel gearing and a horizontal shaft, which transmits power to a shunt-wound dynamo by means of belting. This dynamo is by the Electric Construction Corporation, and develops 65 volts and 35 amperes when running at a speed of 510 revolutions per minute. The dynamo is used for charging a set of accumulators, consisting of 26 EPS cells of the K15 type in teak boxes. The rest of the mechanism consists of automatic apparatus arranged with the view of making it possible to leave the motor unattended during considerable periods. The same difficulty has been met with as is always found in train lighting by electricity, owing to the varying speed of the dynamo. Large sums have been spent upon automatic apparatus for train lighting; it is therefore of interest to examine the method used in the present case. In a direct line with the armature shaft, and connected rigidly to it, is a light shaft provided with a centrifugal governor, which is made to control a double-armed switch, which travels over a series of contacts similar to those of the ordinary charge and discharge switch. With this apparatus it is considered that it will be possible to switch cells in or out according to the pressure produced by the dynamo. We now come to the case in which the cells are being charged, and it is desired to stop the dynamo automatically after a complete charging. This apparatus is somewhat complicated, and although ingenious we fear that it will be liable to get out of order.  

 The whole control is obtained from an ordinary hydrometer in the electrolyte, a movement due of course to the changing specific gravity of the liquid as the process of charging proceeds. As soon as the liquid attains its greatest density the hydrometer rises and closes a small contact, which permits a current to pass through a relay and releases a switch, breaking the circuit through the relay and actuating a clutch which puts contact into motion. This clockwork may be set to run for two, three or four hours as desired, and during that time the cells are still receiving a charge so as to cause thorough boiling. At the close of this period, when it is desirable to cease charging altogether, the clockwork actuates a switch which permits a current to pass into an electromagnet controlling the belt fork gear. The belt gear is an ingenious contrivance, and has a right- and left-handed interrupted or mangle screw. Over one half of the superficies of the screw spindle the left hand pitch predominates, and over the other half the right-hand thread, while upon two lines parallel with the axis there is no thread, as indicated in Fig. 3. Of course, in cutting one thread the other is partially cut away, and the portions of threads end in sharp points. At each side of the screw, which is driven by belting, is placed a half nut normally out of gear with the screw, but put into gear suddenly by the action of one another of two electromagnets. To return to the clockwork for the moment, we observed that it causes a circuit to be closed when the cell charging is completed, the current then passes through one of the electromagnets, and by means of the double-threaded screw the belt fork moves the dynamo belt onto a loose pulley, this leaving the wind motor itself perfectly free to rotate without doing any work. If power is being taken from the cells the density of the electrolyte will fall, and finally the hydrometer will close a lower contact which causes the belt to be put again upon the fast pulley and the dynamo to be restarted. The whole apparatus is theoretically perfect, but we are much afraid that the delicacy of the parts will lead to trouble. Messrs Rollason however are on the right track, and if they can devise a simpler mechanism will succeed. It must always be remembered that for such a wind motor and electrical plant to be of use it must be simple enough to be attended to by a gardener. If a skilled mechanic or electrician is needed it will much diminish its chances of usefulness…it must be remembered that the plant we examined was the first built by the company, and therefore somewhat crude. We are informed that Messrs Edmundsons, of Great George-street, Westminster, have carried out the whole of the electrical work required. There should be great scope for a successful and really trustworthy wind motor for electrical purposes, and we understand that a number of orders have already been received by the company, which is about to start work close to Willesden Junction station, where it will manufacture the complete plants.”