Century Dictionary and Cyclopedia
- n. The exterior wheel of the sun-and-planet motion (see sun).
- n. In the plural, an epicyclic train of mechanism for roducing a variable : angular motion, such as that of the radius vector of a planet in its orbit. The common contrivance for this purpose consists of two elliptical wheels connected by teeth in gear with each other, and revolving on their foci. While the driving-wheel moves uniformly, the radius vector of the other has the required motion.
“In some cases, particularly when annular wheels are used, the train-arm may become very short, so that it may be impossible to mount the planet-wheel in the manner thus far represented, upon a pin carried by a crank.”
“The action of a complete epicyclic train involves virtually and always the action of two suns and two planets; but it has already been shown that the two planets may merge into one piece, as in Fig. 10, where the planet-wheel gears externally with one sun-wheel, and internally with the other.”
“But in attempting to apply this formula in analyzing the action of an incomplete train, we are required to add this motion of the train-arm, not only to that of a sun-wheel, but to that of a planet-wheel.”
“This consists of a fixed sun-wheel A, engaging with a planet-wheel B of the same diameter.”
“Thus the formula leads to the surprising conclusion, that when A is fixed and T revolves, the planet-wheel B will revolve about its axis twice as fast as T moves, in one case, while in the other it will not revolve at all.”
“Now it happens that the only examples given by Prof. Willis of incomplete trains in which the axis of a planet-wheel whose motion is to be determined is not parallel to the central axis of the system, are similar to the one just discussed; the wheel in question being carried by a secondary train-arm which derives its motion from a wheel of the primary train.”
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