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Fig. 8. Device for Winding up Rubber-Band Motors

The height of the blocks N should be about 1/4 inch, although this will necessarily vary with the machine. The blocks should be placed approximately 4 inches from the forward end of the machine. The front end of the forward plane should be elevated about 1/4 inch above the rear end, which rests directly on the main strips.

Both the front and rear planes L and P are removably lashed to the frame by means of ordinary rubber bands, which may be obtained at any stationery store. These rubber bands are lettered M in Fig. 1.

Winding the Rubber Strips. The rubber strips can be most conveniently wound up by means of an egg beater, slightly changed for the purpose. Fig. 8. The beater and the frame in which it is carried are entirely removed, leaving only the main rod E, which is cut off at the lower end so that the total length is not more than 2 or 3 inches. The two brass strips D on either side of the rod, which are attached to the pinion Q meshing with the large driving wheel H, are likewise retained. A washer F is soldered to the rod near its upper end, so as to limit the motion of the small pinion and the brass strips D attached to the pinion. Next a wire B is bent in the form of a loop, through which loop the central rod passes. The ends of the wire are soldered to the side strips D. Lastly, a piece of wire C is bent and soldered to the lower ends of the side strips. In order to wind up a rubber strip, the strip is detached from the forward end of the model, and the hook A slipped over the wire C. The opposite end of the rubber band is held in any convenient manner. Naturally the two strips must be wound in opposite directions, so that the two propellers will turn in opposite directions. By stretching the rubber while it is being wound, more revolutions can be obtained. It is not safe to have the propeller revolve more than 700 times. The ratio of the gears of the egg-beater winder can be figured out so that the requisite number of twists can be given to the rubber bands for that particular number of revolutions.