Orrery Clock

 This is a real one off clock, bringing together many interesting functions.

This is a hybrid clock in as much as the gear train is weight driven by motorised Wagner type remontoire and the balance wheel is energised by magnetic pulses.

The gear train has a lever escapement which is latched and unlatched by the balance wheel. There was not quite enough power for the wooden escapement to consistently power the large balance wheel so the balance wheel was independently powered.

The pictures and video below show the detail in the construction but I shall add some notes.

The balance wheel has a small magnet buried in its rim and as this magnet passes a coil it is sensed by a microcotroller and the coil produces a magnetic pulse which pushes the wheel on. The frequency of the wheel is primarily controlled by the large 'hairspring' . but some sort of regulation is required. This is accomplished by a 'finger' which pushes on the spring and restricts its motion . The finger is driven in and out by a motorised cam controlled by the microcontroller. The time between sensing the magnet on one oscillation of the wheel and the next is measured by the microntroller and this is averaged for maybe 10 oscillations. If the period is less than the required 4 seconds the finger pushes in. If it is more it allowed to move out. The closer the time is to 4 seconds the less the finger is moved. This is PID (Proportional, Integral, and Difference) control, a well used priciple in process contol. Eventualley it stabilises at 4 seconds and becomes an accurate clock, If circumstances change, such as temperature or humidity, it springs into life again to restore the status quo. If you look at the Congreve clock page you can see some typical timing traces for such a controller.

The clock gear train has a lot of work to do in driving the lever escapement and the gearing for the moon phase display and the orrery. A simple motorised winding system is empolyed in which the wooden motor is the train driving weight. Of particular interest is the wooden contrate gear set to turn the drive through a right angle to the escapement.