The windmill is firmly bolted on the wheel-drum of a 4x4 rear axle, secured on a rotating platform. This platform is equipped with a motorized ring that performs the orientation of the windmill in the flow of the wind. It also allows to place it in the bed of the wind in case of potentially destructive storms.
The first section of the tower is wide enough to allow the stirrer to be completely extracted from the main column where it sits.
The length of this first section must be at least 10 meters to allow the windmill to be operating at stronger winds and escape the turbulences of the building.
The last section of the tower is reduced in width, in order to give way to the widmill's blades. It is long enough to allow for further eventual enlargement of the widmill's diameter up to 7 meters.
The motorized ring mechanism allows to orientate the windmill in the wind, according to the anemometer output signal (that is also used by the servo-mechanism to regulate the speed).
The step-by-step motor-brake system, prevents the windmill to be moved-away from its position due to the counter-reaction effect of the high-torque stirrer.
The rotation mechanism of a small tower-crane could be used for this purpose.
The windmill is mounted on the rear-axle of a 4x4 car, that performs the 90° horizontal to vertical conversion of the movement. This type of equipment is very sturdy, reliable and consistent with the stresses to be handled. It can be easily found in a second-hand shop.
The differential axle is then secured on the rotating platform.
The top of the column can be opened by removing the insulating cover made of rigid polystyrene foam and divided in 4 parts. Access is then given to the stirrer for maintenance.
The shaft of the windmill is equipped at each end with cardans that absorb the slight misalignment between the "differential" output of the rear-axle, and the axle of the stirrer's rotor.
A caoutchouc silent-block is inserted in the shaft to absorb the shocks generated by the sudden variations of the wind-speed. Another function is to electrically isolate from earth in case of a lightning striking the metallic tower.
The shaft should be easily removable to allow extraction of the stirrer for maintenance.
One can see on the following top-view drawing, that when the inflatable shock-absorbers on the sides of the stirrer's cage are deflated, the complete stirrer can be hoisted up into the tower structure in order to be maintained or replaced.
When the stirrer needs maintenance, it is first hoisted into the lowest section of the metallic tower. Then a few members of the tower are provisionnally removed on the southern side, on a day without wind. The stirrer is then rolled out of the tower thanks to an integrated retractable bridge-crane and lifted down on the terrace of the buiding. First level of maintenance can be performed there.
We have seen in the 5th chapter that an alternative to the reinforced concrete main column, would be to use the first section of the steel-mast of a conventional industrial wind-generator.
The same approach could also concern the metallic tower of the windmill. Instead of the specific design mentioned hereabove, it could be economically more advantageous to use partly the last portion of a conventional tower-crane widely used in the field of construction.. It would have to be slightly modified to interface with the steel-mast.
The upper portion of the tower, as well as the orientation motorized mechanism could perfectly fit our application.
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