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A compact, gravity powered clock. There are many Lego clocks around, but most of them are really huge contraptions, and for a good reason. They are easier to tune, more eficient, work longer... So naturally I took a challenge to make something small but still usefull :P. The key component is the pendulum. Typically, a significant length is needed to get period of one second. Here, a second mass over the pivot point slows the tiny pendulum down, so that it can be many times shorter than usual. The compact "knife edge" pendulum suspension dramatically reduces friction, decreasing the power necessary to run the piece. The low mass of components creates many problems. The clock is reasonably accurate (I got it within 5 seconds per hour), but tuning was a nightmare, and even a sneeze can alter its rate. The power source is 100g weight on a string. Due to only one hour working time, I have decided to use only minute hand. Seconds hand puts too much power demand on the mechanism.

33962383790_5e60f95d29_c.jpg1 by David_Z1, on Flickr

34346229125_7f0c9d2168_c.jpg3 by David_Z1, on Flickr

34305441546_6103e3a312_c.jpgSchem2 by David_Z1, on Flickr

 

Many thanks for KEvronista for inspiration to get into this Lego clockmaking hobby :)

[EDIT]: embedded the video.

Edited by Davidz90

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3 hours ago, Davidz90 said:

So naturally I took a challenge to make ...

And that, my good Sir makes you the kind of builder I like!:thumbup:
It looks intriguing, complex and minimalistic at the same time, the only suggestion I have for you is... VIDEO!!!!:laugh: I'd love to se your creation in motion.

 

Keep up the good work!

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Nice start to make a clock. Like the mechanism. Don't like the non-LEGO parts. I used a few 53g boat/train weights ( 73090b ) in my own self-winding and self-adjusted clock, which is not very large, much smaller than most LEGO clocks. There is also the steel counterweight ( 70163 ) available that can be used in the pendulum. So far I should not call this a clock, more like a machine that ticks. I don't see why a geared downed hour hand would increase the friction on the pendulum more than marginally. Keep up the progress, you have many inspiring challenges before you! 

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32 minutes ago, Gonkius said:

Nice start to make a clock. Like the mechanism. Don't like the non-LEGO parts. I used a few 53g boat/train weights ( 73090b ) in my own self-winding and self-adjusted clock, which is not very large, much smaller than most LEGO clocks. There is also the steel counterweight ( 70163 ) available that can be used in the pendulum. So far I should not call this a clock, more like a machine that ticks. I don't see why a geared downed hour hand would increase the friction on the pendulum more than marginally. Keep up the progress, you have many inspiring challenges before you! 

Hour hand is not a problem. Just for the one hour operation, it didn't seem all that usefull. I'm going to keep the current, short drivetrain and make it self-winding. I'll surely try to obtain the lego weights. How much does the counterweight weight?

BTW Your clock is a real masterpiece, especially the self - adjusting is very clever.

Apart from electric remontoire, another idea I'd like to try is electromagnet in the base impulsing the pendulum directly, at 1Hz rate. Then, the pendulum drives the mechanism. Theoretically, that would be super accurate.

Edited by Davidz90

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The counterweight is 11.5g each according to my scale. Length is slightly less than 4 studs with one cross axle hole. I'm planning to make a gyro stabilization using a lot of these in another build I'm working on. The larger boatweight is about 55g. 

Any idea how to make an electromagnet using LEGO parts? Probably very difficult to adjust a pendulum frequency by using an external force however. 

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I have one broken LEGO electric motor waiting to be taken apart. Maybe the motor windings can work as a electromagnet. Alternatively, for example shadow_elenter has incorporated third party electromagnet inside PF motor housing.

I'm not planning to directly adjust the pendulum by external force. Instead, the electromagnet will be powered by 1 Hz sine wave (I'm looking for ideas how to do this. Mindstorms is pricey.). Then, the pendulum becomes a driven oscillator, with exactly 1Hz frequency. If the natural frequency of the pendulum is off, then we are away from resonance, and amplitude becomes smaller, but still it has no effect on the rate.

 

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Forcing a pendulum, by using an electrognet, to a frequency that is even the slightest off its natural frequency will need larger forces than you expect, to get any amlitude at all, just a warning from my side. Everyone has got their own threshold what is acceptable modifications to LEGO pieces. My simple rule is that any modification that cannot be undone is not accepted, I would never convert a motor to an electromagnet by replacing the inside as I read in another thread, but that's me, you are free to think otherwise. If you in any case will have an electrical timebase in some way, you could always build a stepper motor, similar what you find in quartz watches.

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Just a small update. I have reworked the clock to extend the operating time to 50 hours. This was possible with very small and reasonably efficient Arnfield gravity escapement. Basically, the pendulum lifts small weight (right arm) from upper position to the lower position. The difference in height, which equals to difference in potential energy, is transferred to the pendulum. Then, the pendulum swings free. In the meantime, the weighted arm unlocks the escapement wheel and is lifted by it back to the upper position. The smooth, shock free operation allowed for very light pendulum and good overall efficiency. 

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Another update. This time, a grasshopper escapement has been used to set (probably) a new record of lego clock efficiency.

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This is great.

Although i'm always a bit put off by the friction fitted precision parts, clocks are my favourite type of technic model.

I'm still hoping for an official model :sadnew:

PS: have you tried using a pull-back motor as energy storage?

Edited by schraubedrin

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18 minutes ago, schraubedrin said:

This is great.

Although i'm always a bit put off by the friction fitted precision parts, clocks are my favourite type of technic model.

I'm still hoping for an official model :sadnew:

PS: have you tried using a pull-back motor as energy storage?

All my previous designs were too sensitive to changes in driving force to make pullback practical. I'll definitely give it a shot with grasshopper.

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Yet another clock. This time, with heavy, long pendulum, allowing for much better accuracy. Running time is 48 hours - this one is quite power hungry!

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Do you have instructions or LDDs of your models?

I love lego models of complex mechanical devices. They really help to understand them thoroughly.

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Sorry, I don't have instructions and don't really have enough time to make them. However, most of my models are very open-framed, with pretty much everything visible. That said, some escapements really need some trial and error and fine manual adjustments to start working properly.

For example, my last big clock is constructed around this escapement:

which is super easy to make, with around 20 pieces. The rest is easy - just a long drivetrain with 1:625 ratio, the clock shape is not critical as long as structure is sturdy.

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Another design in microwatt power range. Combines very long period pendulum with "spring" made of carbon fiber strip.

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Very cool! Those mechanical clocks are fascinating and since the pullback TC I wanted to build another one. Do you have a good reference on escapements, especially the Arnfield? I’ve not yet found a good one online.  

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13 minutes ago, Ludo Visser said:

Very cool! Those mechanical clocks are fascinating and since the pullback TC I wanted to build another one. Do you have a good reference on escapements, especially the Arnfield? I’ve not yet found a good one online.  

Ken Kuo has many excellent animations of various escapements:

https://www.youtube.com/channel/UC2h07cGBpJs8bF3OkgtJICg

 

Other than that, there are many other animations. As for books etc, unfortunately I don't know any good references. 

The Arnfield, while conceptually a bit more advanced than other escapements, is actually pretty easy to pull off. The critical part is making sure that unlocking the escape wheel takes less energy than the wheel delivers by lifting the gravity arm back up. Basically, the escapement tuning is like this:

gravity arm fails to lift? -> it has to be lighter or more torque is needed

gravity arm jumps erratically? -> less torque or heavier arm is needed

escape wheel fails to unlock? -> needs heavier gravity arm or less unlocking friction

pendulum works for a while then stops? -> needs heavier gravity arm or less unlocking friction

 

I have done recently an instruction for my Arnfield escapement:

 

Edited by Davidz90

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And now something slightly different: an orrery! 

It was a challenge to get proper orbital periods with possibly simple gear ratios. The result: 99.87% accuracy!

 

 

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Orreries are awesome!

Very impressive how you figured out all the gear ratios. And there's some clever constructions in there, like the old clutch gear with the plate-with-hole locking into it to have the Moon revolve around the Earth. I need to order me some more 40z gears, see if I can duplicate it! Do you have maybe also some still photo's?

P.S.: if you line up those u-joints, the motion of the Moon will be quite a bit smoother.

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Thanks! 

Figuring out gear ratios took me more time than actually building the thing :D

Lining up u-joints is definitely a good idea. Another thing I'd like to improve is to use a large turntable for frame rotation - that would be much less wobbly.

Sure, I have few photos on Flickr:

28456958907_f6da953610_b.jpgOrrery_5 by David_Z1, on Flickr

41516337330_b436af7a05_b.jpgOrrery_1 by David_Z1, on Flickr

41516332010_2a0358fc7e_b.jpgOrrery_2 by David_Z1, on Flickr

41516328680_1b035b4787_b.jpgOrrery_3 by David_Z1, on Flickr

43325880951_4401f77a1d_b.jpgOrrery_4 by David_Z1, on Flickr

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A final version of my Arnfield clock, and my first wall-hanging design.

And here are building instructions for escapement:

 

Edited by Davidz90

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Very nice. The video explains it well, although in the black&white version at the end it's a bit hard to see what's what.

Thanks also for providing the building instructions - I keep saying I have to build one myself, but now my only excuse left is that I don't have the screwdriver :grin:

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