Electromagnetic pendulum clock motor

**DickB** · 11-06-2011

This is a clock motor for an upcoming clock project, a variation on my Naked Clock. I'm not the first to do this, but I did need to test the concept of making parts with the CarveWright and get started on my new clock design. This is a test mule.

In most clocks with pendulums, the pendulum regulates the clock but does not drive the mechanism. Electromagnetic pendulums do both. Since the pendulum is driving the clock, the usual escapement mechanism is replaced by a pawl and ratchet wheel or the like. The pendulum has a small rare earth magnet at the bottom and a fixed coil in the base, typically hidden. As the pendulum swings toward the coil, the magnet induces a voltage, first a negative pulse and then, as it moves away from center, a positive one. An electronic circuit detects the positive voltage and then applies current into the coil, producing a repelling magnetic force. This keeps the pendulum moving.

There are several two-transistor drive circuits floating around, but they are generally finicky. I came up with one using op amps that triggers reliably and allows the drive pulse width to be tuned. The LED is just for show. I have intentionally left the ratchet wheel and parts a little rough, and applied some friction to the wheel, to make sure that the pendulum is capable of driving a clock mechanism even if it is not perfectly tuned. I'm running the pendulum from a 3 volt power supply, but intend to use a couple of D cells or the like in the finished clock.

It's important to note that the period of the pendulum is set by the length and mass of the pendulum, not the electronic circuit. So the final pendulum will have an adjusting wheel or the like. However, I plan to experiment with a microcontroller circuit to see if I can "influence" the pendulum enough to keep perfect time. This pendulum's period is one second, so the 60-tooth ratchet wheel turns once per minute. It could be used to drive a second hand, and basically replace the 1 RPM timing motor in my Naked Clock.

**Digitalwoodshop** · 11-07-2011

VERY Impressive.... And the Clock too.... The O'Scope.... Sorry.... I was a Test Equipment Calibrator at Sony for 2 years... I have a fondness for Test Equipment.... Excellent Clock !!!!!

AL

**dbfletcher** · 11-07-2011

Really cool! I love this kinda stuff. I just started playing with the Arduino platform earlier this year. I really wish I just had more time to play with all the stuff that interests me.

**b.sumner47** · 11-07-2011

You lost me on this one. I'll wait for the results.

Capt Barry

**Jeff_Birt** · 11-08-2011

Very neat stuff. I like that fact that it has some hi-tech juxtaposed with low-tech.

**gapdev** · 11-09-2011

Sign me up!

Kenny

**DickB** · 11-15-2011

I've done some more research and made some improvements to this clock motor. The biggest change was to add a ramp drive mechanism like those of John Pickron. Under the original setup, the pendulum directly drove the pawl. The problem is that the span of pawl travel would vary with the length of swing arc of the pendulum. As batteries wear down, for example, the pendulum arc length gets less, and the pawl could miss the next ratchet tooth. This could be compensated by more complex drive electronics. But the mechanical solution is IMHO more interesting to see operate. Adding a ramp with a circular curve towards the end of travel limits the length of pawl travel. With simple adjusting mechanism, this length can be easily tuned to the distance between teeth on the ratchet wheel when the clock is built.

I also put more aggressive teeth on the ratchet to prevent the pawl from slipping out. With this setup, the motor is working very reliably. You can see I am also starting to convert the simple, even ugly parts into more elegant forms that will be used in the finished clock.

Next step is to fine-tune the length of the pendulum, make it more elegant, hide the magnet, and provide for weight (and therefore period) adjustment.