Epicyclic

Wheels Within Wheels

This is a clock of unusual design  with all the reduction stages realised with epicyclic gear sets in series. The clock stands 30cm high and the chapter ring is 15cm in diameter.

The motive power is a Kundo style electromagnetically impulsed pendulum where a magnet swings through a wire wound  coil. By firing a pulse of electricity through the coil at the appropriate moment the generated magnetic field repels the magnet and the pendulum keeps swinging.

To keep the pendulum short but with a reasonably long period it has been configured as a compound pendulum with the adjuster on the top.

A pawl and internal ratchet wheel converts the oscillations of the pendulum to rotary motion. This can be seen in the video below. The pendulum has a period of 0.882......  seconds which means the ratchet wheel must have 68 teeth if it is to rotate once per minute.

The output of the of the ratchet wheel is applied to the sun (or central) gear of the first epicyclic and with the outer ring held stationary the output is the carrier. The  first set gives a 7.5:1 ratio.

The output of the first set is passed to the sun gear of the second and the output is again the carrier. This set has a ratio of 8:1 and the carrier output drives the minute hand.

The third set gives a 12 :1 reduction and drives the hour hand. The ring gear conveniently forms the chapter ring. A single planetary .gear has been used for this stage, mainly just for fun, but two wheels could have been used. Three planetary gears would not have worked due to limitations in the teeth count.

The coil is formed of 24swg wire and has a resistance of about 50 ohm and has 70g of wire wound around a piece of 15mm copper pipe. The voltage pulse applied is 5v for a 60msec. The timing is accomplished with a small microcontroller (Arduino Nano). As the magnet passes through the coil a voltage is generated and this is sensed by the controller. It then immediately fires the pulse to impulse the pendulum.

 

YouTube Video