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Lazy Clock

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Project by DickB posted 02-20-2013 06:52 PM 1945 views 6 times favorited 10 comments Add to Favorites Watch

This is the third wood-gear clock that I designed and built. I call this one the “Lazy Clock” because it ticks only once per minute. It uses an unusual, if not unique, mechanism – a solenoid-driven ratchet. The electrical coil is fired once a minute by a battery-powered microcontroller circuit, and that advances the minute hand. Because it ticks so infrequently, the gear train is much simpler than most clocks, making this one of the easiest wood-gear clocks to build.

My goal was to get this clock to run for a year on two AA cells. The solenoid had to be very low power, so there is a delicate balance between having enough power to reliably run the clock and conserve electricity. I used a rare earth magnet for the solenoid core to help achieve this. Well, I think I have achieved it – I’ll let you know in a year!

The back of the prototype is 3/4” mahogany and the face 3/4” hickory. The wheels (larger gears) are 1/4” Baltic birch. The pinions, hands, and other parts are 7/16” oak or maple. I built a second clock of all Baltic birch and maple.

I built the clock using a Carvewright CNC machine and designed it with that machine’s Designer software. Sorry, there is no way to export to other CNC formats. However, except for the carved face, the rest of the clock could be built with conventional tools such as a scroll saw and router. So, if anyone wants to design their own face and build one of these, I have extracted templates and published them on my we site here.

(If the link doesn’t work, copy and paste this: www.carveshop.com/html/lazy_plans.html )

If you do build one, I’d love to hear from you.

-- Dick, http://www.carveshop.com





10 comments so far

View Jamie Speirs's profile

Jamie Speirs

4163 posts in 1611 days


#1 posted 02-20-2013 07:36 PM

Dick that is a very clever clock, one tick is brilliant
I like simple, the solenoid sound very interesting.
Jamie

-- Who is the happiest of men? He who values the merits of others, and in their pleasure takes joy, even as though 'twere his own. --Johann Wolfgang von Goethe

View Gerben's profile

Gerben

112 posts in 1110 days


#2 posted 02-20-2013 08:54 PM

I was thinking of someday making an battery powered clock, but batterylife would be a problem. Your once a minute is a very elegant (not lazy) solution. You’ve given me some food for though.

Also, nicely build.

View Surfside's profile

Surfside

3372 posts in 928 days


#3 posted 02-20-2013 10:15 PM

You’re a wizard! That’s a indigenous work! That is great. Keep it up .

-- "someone has to be wounded for others to be saved, someone has to sacrifice for others to feel happiness, someone has to die so others could live"

View DS's profile

DS

2132 posts in 1174 days


#4 posted 02-20-2013 10:56 PM

I LIKE IT!
Good job!

-- "Hard work is not defined by the difficulty of the task as much as a person's desire to perform it.", DS251

View Ken90712's profile

Ken90712

15337 posts in 1943 days


#5 posted 02-21-2013 02:27 PM

Great work and design on this clock. I think from an engineering standpoint you nailed it, the longevity of the batteries with that low power distribution the life expectancy will be interesting. It’s got some great colors as well.

-- Ken, "Everyday above ground is a good day!"

View DickB's profile

DickB

65 posts in 1073 days


#6 posted 02-21-2013 03:10 PM

Thanks. The grain in the hickory really popped with the oval shapes.

It’s an interesting clock to have around. The ticking is not exactly quiet; even so, sometimes you notice it and sometimes not. Here’s a short video of an early prototype ( http://youtu.be/hnko9fZRO-w )

It’s hard to know just how long the clock will run, because the average current draw is so low it is off the battery spec sheet chart. Not sure where to extrapolate. I designed a test mode into the electronics where the clock ticks once per second (and of course runs fast) to allow the builder to look for and find problems in the mechanism. I thought about running the batteries down in test mode to measure length of service, but the 60x current draw would influence the results. These batteries have less capacity the higher the current draw, so the extrapolation would be incorrect.

I do have some ideas for other novel drive mechanisms – I’m experimenting with a single-coil stepper motor that uses four magnets in a disk right now. But it is relatively high power and will probably require a wall wart power supply.

-- Dick, http://www.carveshop.com

View Fishinbo's profile

Fishinbo

11353 posts in 930 days


#7 posted 02-21-2013 05:17 PM

Impressive work! The clock is great looking and the mechanism is just awesome.

View Gerben's profile

Gerben

112 posts in 1110 days


#8 posted 02-21-2013 07:30 PM

Too make it quieter you could try using the solenoid to lift some weight, and have the movement back push the gear one position. I hope this makes sense.
The solenoid delivers a lot of power in a short time, while gravity can deliver the power more gradually. This could, maybe, also reduce the change of tooth skipping.
Just my 2 cents.

I liked the video’s you added. They show how the mechanism works a lot better that pictures can.

View DickB's profile

DickB

65 posts in 1073 days


#9 posted 02-21-2013 07:57 PM

Good idea. You are correct that a solenoid usually delivers a lot of power in a short time. But in my case I programmed the microcontroller to ramp up the current in the solenoid using a technique called pulse width modulation, primarily to avoid the sudden snap action that is typical. I could actually engage the solenoid gradually over several seconds – in fact, I did this as a trial – and also de-energize it gradually. It makes for a nice, smooth, and somewhat more quiet action, but at the expense of way too much power for battery operation. So again, the trade-off is noise as well as reliability versus power. I actually spent quite a bit of time tuning the software. I’m still playing a bit with one of the clocks. Your suggestion has prompted me to do some tuning on it to minimize noise and ignore power draw – it might make a nice wall wart-powered desk clock, which is where I have this clock as it happens. The other clock has been running reliably for about a month now on the wall in my garage/shop. Dust in the works is not an issue!

-- Dick, http://www.carveshop.com

View Gerben's profile

Gerben

112 posts in 1110 days


#10 posted 02-21-2013 09:07 PM

I know about the PWM. I had a look at the source code you provided :-). I just started to learn about using an AVR/arduino. Another fun but time-consuming hobby, just like woodworking.
If you are using the gravity-powered back-movement you could possibly do without the pwm, conserving even more power. Though, that would indeed make more noise.

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