Stage 6 - The Dragon

The position of Caput Draconis in the sky is represented by a symbol which is attached to wheel 177 - the dragon’s wheel. This must rotate at slightly less than the speed of the sun, such that the sun laps the dragon’s head once every 18.6 years. Each time the dragon’s head passes the moon (i.e. every 29^1/2 days) the moon’s model must dodge the dragon by moving outwards, returning after the dragon has passed. In the nineteenth year this manoeuvre must put the moon under the shadow of the earth.
		A bracket attached to the sun’s tube carries a transported gear train. The bracket rotates once per solar day and in doing so causes pinion 6 to drag wheel 177 round with it. At the same time bevel wheel 24 is carried around bevel wheel 38 on the star tube.
		The latter is of course rotating at almost the same rate as the sun’s tube, so the drive to wheel 24 is equal to the difference between their speeds, i.e. one turn per year. This motion is transmitted to pinion 6 which very slowly rotates, cranking wheel 177 backwards to achieve the desired rotational speed.
In one year bevel wheel 38 makes one complete turn relative to the bracket attached to the sun’s tube. Consequently bevel wheel 24 makes 38/24 turns, as does pinion 6. So, as wheel 177 is driven it is at the same time cranked backwards by 38/24 X 6/177 turns per year. Thus in 18.6 years wheel 177 is cranked backwards by 18.6 X 38/24 X 6/177 = 0.998 turns
Each time the dragon approaches the model of the moon, 5 pins attached beneath the dragon’s symbol engage with pinion 12 which is connected to pinion 32. When the latter rotates it causes the rack to slide outward and so move the model of the moon outward, using two wire stirrups.
	As the dragon’s head passes, 5 more pins engage on the opposite side pinion 12 to rotate it in the opposite direction and to pull the moon back. The moon is not fixed onto its shaft, but the shaft has a keyway so that the moon can slide along but must still rotate with the shaft.