Page:Popular Science Monthly Volume 88.djvu/499

 Popular Science Monihly

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��heavy spring brass sheet. It should be bent, as shown in the drawing, and held securely at one end by a small wood block and screws. A stout, flexible cord should be fastened to the upper end of the lever arm and led out to a small pulley, from which it should hang within reaching distance of the floor. When the opening door causes the peg to strike the trigger and open the circuit, the cir- cuit breaker should be re-set by pulling the string Although not entirely ad- visable, the helical spring may be omitted, and a weight suspended from the lower end of the string so that when the door is closed, the breaker will be re-set automatically-

Connections of the various pieces of apparatus should be made as indicated in the accompanying diagram.

Briefly, the operation of the electric garage door-opener, is this : When the wheel of the automobile runs upon the board in the pit, the car should be stopped. The current from the line flows through the contacts and into the motor ; the pulley revolves and draws itself, al- most literally, along the rope, thus open- ing the door. When the door is opened, the peg strikes the trigger and the cur- rent flow is shut off.

There are various other ways of in- stalling the motor and driving mechanism upon the garage door, but the one de- scribed is undoubtedly the cheapest. However, in case the clearance of the automobile roof is very small — too small to allow even for the small space that the rope occupies — the motor may be in- stalled on the door jamb, and a bicycle cog mounted on the end of the shaft. A long bicycle chain should pass from this cog to another on the opposite jamb, and one of the door pulleys attached to the chain. Another method which would be simpler, perhaps, than either of the foregoing would necessitate only the in- stallation of a magnetic release and a heavy weight operating through pulleys. If electricity were not convenient, a wa- ter motor could be used, or a water or compressed-air plunger, working on tbe principle of the plunger elevators, would give fairly satisfactory results. It is quite evident that much originality in construction is left to the builder.

��Mounting Spark-Gaps to Eliminate Unnecessary Noise

A NOVEL and very good method of eliminating most of the noise made by a rotary spark-gap in operation, is shown quite clearly in the illustration. The rotary gap, with its motor, is mounted in a substantial wooden cabinet, with a glass door. This cabinet is then suspended on four strong spiral springs, from the underside of the operating table. It is advisable to have the glass door on the cabinet closed tightly, so as to con- fine all possible noises and vibrations to the wireless room.

����The springs eliminate most of the noise made by a rotary spark-gap in operation

Winding Tuning-Coils

A METHOD of winding tuning-coils so as to increase their durability and quality should be of interest to wireless amateurs. Most of those who wind their tuning coils and loose couplers with enameled wire find that it is hard to keep them from rubbing when the slider pass- es over the turn. This occurred with a coil which one correspondent has been using and which is wound with enameled wire on a hard rubber tube.

To prevent this loosening of the turns, one should, before winding the coil, wind an even layer of tire tape over the tube, and thereafter wind the wire over it tightly. This scheme will also prevent the wire from loosening much on a coil, wound on a wooden core, which may shrink. Soaking in paraffin also prevents shrinking of wooden tubes.

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