Davidz90

Exactly. A reset mechanism that pulls the faster hand back by several rotations and puts it exactly at 0 seems really difficult to do reliably. It seems that adding a slip clutch between hands and using some lever arrangement like in the gray video, that independently forces both hands to 0 position, may be a better approach here.

Frankly, I have no idea.

There is no standard. Usually chronographs have only one hand that counts to 60 seconds. When using the same dial, second hand could show up to 60 minutes. But for that a completely different mechanism than the one I've built would be needed. Resetting would get rather complicated.

This is intended. There is no need for more than one rotation unless there are two hands.

I have found one more good explanation of how this works:

Sure, feel free to ask.

Unfortunately, I have no idea how it looks exactly. However, here is a mechanism I have built just now: I hope this will give You some ideas.

It seems that by pushing a button, he pushes some lever to a horizontal or vertical position. The lever is connected to the hand with some large gear ratio.

Two ways: 1. Weight on a string, hanging from a spool 2. Weight on a lever, connected to the hand with some high gear ratio.

Hi and welcome to the forum! Usually, in real clocks chronograph uses a whole set of special-shaped cams to do the job; see: https://www.fratellowatches.com/understanding-the-mechanical-chronograph/#gref That is difficult to do with Lego. However, a simpler option is to use a weight on a string or a pullback motor attached to the chronograph hand. Then, you need some sort of a clutch to: 1. Connect the hand to the clock. Hand goes forward and lifts the weight or winds up the pullback motor. 2. Stop the hand. 3. Disconnect the hand from the clock. Weight/pullback motor resets it.

Thanks!

Congratulations to the winners, top 2 is so close! Also, thanks for all the votes, way more than I expected :)

Now this is unique! I wonder if the linkages to the wing tips could be altered so that the wingtips perform more of a flapping motion instead of keeping constant angle, which seems a little unnatural.

A little hybrid between a pendulum and balance wheel. Basically, the vertical part acts as a pendulum and the wheel adds inertia to slow it down. The result is a very compact, if inefficient, mechanism.

Wow, that's really unique! Never heard of such machine.

True, there are a lot of fantastic, unique entries. How I wish there were more official Technic sets like that instead of just car after car with some construction equipment in between... Anyway, deciding on the vote was definitely a challenge. I had a lot of fun with this contest.

Thanks! I have tested multiple ways to power this before settling on four weights, getting a good running time out of something this short was a challenge. Auto-rewinders tend to be noisy and I want to actually use this everyday, so heavy weights were the only option. I'm considering replacing the current weights with some sort of a single, ring-shaped one runing along the central leg for a cleaner look. There was also an option of making the leg thicker and hiding the weight inside, but for that I'd need something with really high density like lead or tungsten.

I'm proud to present: A time table! Terrible puns aside, this is a table that tells time. Takes less space than full grandfather clock and is useful as a table (as long as nothing extremely heavy is put on it).

Very impressive! I'd love to see some details of the chuck as well.

He did not, it does indeed speed up quite a bit when rewinding, as shown on my plots. However, that is not a problem in itself, as long as speedup is consistent. In general, there are two solutions to avoid speedup: 1. Make the rewinder as slow as possible. That reduces the extra force exerted by rewinder when it runs. 2. Use an escapement that doesn't care about extra force. You are correct that weight climbing up a chain is less problematic than other rewinder types. The chain acts as a separation between motor and escapement, making the extra force smaller. That's the main reason why I used this type of rewinder in my contest entry.

Wow, the timelapse looks so cool! Maximum error of 40 seconds in 12 hour run is really good! Thank you for the data, I'm back with some interesting stats. The activations of autorewinder are easily visible on the audio recording. When it runs, the clock is considerably faster; for a moment, double period drops from 2.05 seconds to about 1.9 seconds (explanation why I'm using twice the period is below). Interestingly, in times between rewinds, period is slowly increasing. This means that driving torque is decreasing as the weight goes down. One potential cause is the string pooling up on the spool; the more string there is on the spool, the larger its effective radius becomes, resulting in more torque, Next, we can look in detail at the audio signature: There is a pronounced asymmetry in the escapement, with every second tick being much louder than the other; this is also audible in the video. Moreover, times of the left/right swing differ significantly, with 0.6:0.4 ratio. Apart from ticks caused by escape wheel impacting one of the the pallets, there are also weaker sound signatures of escape wheel slipping out of the pallet. Due to that louder/quieter tick phenomenon, it was easier for the program to catch only the loud ticks, so all periods are doubled. Next, period histogram: There are two main peaks corresponding to autorewinder being on and off. The mean is remarkably close to two seconds, with 0.2% error. This corresponds to about 3 minutes/day. This is more or less in agreement with the 12 hour timelapse. Interestingly, the clock is actualy better in timelapse, with about 1.5 minutes/day. Finally, the total error. Here, the impact of autorewinder is the most visible. Between rewinds, clock is consistently too slow, accumulating error. During rewinds, the error is reduced.

"Suspense" - abstract balance wheel clock Unlike 99% of all Lego clocks, this one uses a balance wheel oscillating back and forth, like in a wristwatch. Moreover, to make it even more unique, it consists of 3 separate parts connected by a chain loop. It all started from the idea to use Indiana Jones whip as a suitably weak spring and a ball pin as a low-friction bearing. The whole combo is still nowhere near as good as a pendulum, but can serve as a rudimentary oscillator. The top piece contains the escapement mechanism. It is a so-called chronometer escapement. It delivers a short, strong push to the wheel every time it passes the middle point where the whip spring is not twisted. At this magical point, applied force doesn't alter the period (math behind this is fascinating, but a little beyond the scope of this topic :) but here's a simple explanation with a pendulum example: pushing the pendulum forward on its way down helps the gravity, so pendulum speeds up. Pushing the pendulum on its way up fights the gravity, slowing it down. Pushing it in its lowest point does neither). Only thanks to that fact, I could get any semblance of accuracy with a balance wheel that has a low efficiency compared to a pendulum, so the pushing force needs to be rather high accordingly. Middle part is auto-rewinder that doubles as a driving weight. It is hanging on the left chain, climbing it periodically so that the whole chain loop rotates counterclockwise. It uses a system of levers to apply sufficient force to on/off switch without affecting the clock too much. The face hangs at the bottom, hands are moved by the cycling chain loop. Stats: The balance wheel is very power hungry, auto-rewinder has to activate every 5 minutes or so. Long-running clock without autorewinder seems impossible. Spring power is impractical as well. The most important goal was to make this clock accurate, and I managed that. The average period was 2.0012 seconds with target of 2 seconds, which is 0.06% error. This means that the clock will be off by about one minute after a day of working. Short-duration runs confirmed this, showing about 1 second of error after 30 minutes (so 48 seconds in a day): These short runs were analyzed by recording the ticking sound and running the file through a computer program I wrote to calculate all individual periods. I also did some longer tests, which were slightly less impressive. A 6 hour run ended up with 47 seconds of error, indicating that about 3 minutes/day is a more realistic estimate. A big problem is temperature stability - not only thermal expansion changes the inertia of the wheel, but the elastic properties of the whip change with temperature too. In wristwatches, a lot of research goes into new, exotic spring materials to combat just that. Video of the clock: Link to the topic:

wow, so well done!

First of all, I'm completely blown away with all TC28 entries. I can't even start to compete with them. In the meantime, aside from my 100% Lego entry, I tried a proper steel spring for the balance wheel. It makes a huge difference, making lever-type escapements (what is typically used in wristwatches) possible. They keep the advantage of pushing the wheel only in the middle, but in addition are self-starting. Wristwatch must start automatically after a stop and rewind.

Absolutely beautiful! The concept, looks, delightful sound of the cycling detents...