Davidz90

Very nice model and pretty unique topic! (regarding engine itself, this concept has been tried multiple times in the past, there are severe limitations related to mach number, noise, safety of exposed blades... I'm skeptical, but that's offtopic )

Not exactly. Sidereal day is about 23 hours, 56 minutes - 4 minutes shorter than solar day. Sidereal year, on the other hand, is about 20.5 minutes longer than solar year. So: solar year takes 365.2422 solar days, 366.2422 sidereal days. sidereal year takes 365.2563 solar days, 366.2563 sidereal days.

Here's my schematic: orrery_2 by David_Z1, on Flickr

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. 1 by David_Z1, on Flickr 3 by David_Z1, on Flickr Schem2 by David_Z1, on Flickr Many thanks for KEvronista for inspiration to get into this Lego clockmaking hobby :) [EDIT]: embedded the video.

Thank you very much! Indeed, the magnets provide a huge boost in accuracy - the fact that even doubling the driving weight changes the clock speed only by ~0.02% is kind of insane. I think that actually the most difficult part was having enough patience - a good 3 days of correcting the period by few microseconds, then waiting half an hour for the pendulum to reach a steady state to evaluate the speed...

There is definitely something wrong with the numbers in this video. I'll try to make some diagram, but the numbers I posted on march 18 are correct ones. Regarding the turntable stuff - he basically alluded to the whole solar/sidereal time issue. We are used to solar days/years, but all rotations in the orrery are in relation to the crank that is fixed to the base. So for judging accuracy, we need to compare the rotations to sidereal day and sidereal year (=true 360 degree rotation in relation to fixed stars).

Final design of my high accuracy clock. In short: less than 1 second of error in a day, less than 3 seconds in a week. Beats high-end mechanical wristwatches and medium quality grandfather clocks, and approaches the accuracy of low-end quartz mechanisms.

I'm proud to present a strong contender to the title of the most accurate Lego clock in the world. It all started from a stable base: Lego tower sandwiched between wooden boards and the base contains ~15 kg granite slab. This sort of extreme build was needed to keep structure vibrations in check with ~1 kg swinging pendulum. The final (for now...) clock is here: Just now, I finished a 23 hour measurement of clock accuracy. The pendulum is intended to have 2 seconds period. Here's how it actually is: period_24h by David_Z1, on Flickr basically 2 seconds +-300 microseconds. However, what we care about is the total error of the clock (how much it is early/late), which is a sum of the errors of all periods: error_24h by David_Z1, on Flickr The clock started on time, at ~2 hours it was 0.6 seconds early, near 9 hours it was 0.8 seconds late. Less than 1 second error in 24 hours is a Rolex-level accuracy (in fact, a little better than any mechanical watch). And now some technical details: The key component of the clock is grasshopper escapement (invented by John Harrison, it is one of the most accurate clock mechanisms). It's characteristic feature is that within some limits, clock speed is independent of amplitude. Due to the technical limitations of Lego (too much friction), I couldn't get that - the clock speed depended on amplitude/driving force, which is always a little variable due to friction. In order to combat this, I devised a magnetic compensation system - two magnets on the sides of the pendulum, pulling it away from center. As the amplitude increases, the distance between magnets at the pendulum at full swing decreases. By pulling the pendulum away from center, the magnets fight the gravity, and thus slow the pendulum down. The slowdown depends on magnet distance, so it is a function of pendulum amplitude. This amplitude-dependent slowdown counters the amplitude-dependent speedup of the mechanism. With this system in place, the clock speed looks like this: mag_s4 by David_Z1, on Flickr Clock rate is the standard way of measuring speed - rate of 1 seconds/day means that after 1 day of working, clock will be 1 second early or late. You can see that near 4 degree amplitude, rate is not changing much at all. This is astonishing stability - 1 second/day means 1/(24*3600) = 1/86400 - about 10 parts per million! Second key component is the compensation of thermal expansion - as it gets hotter, pendulum expands and clock slows down. This is especially bad with ABS plastic. I fixed this by hanging the pendulum weight on steel wires, and then using the expansion of bricks to compensate the smaller expansion of wires. The system is described in the video and currently is over 90% efficient (the dependence on temperature is decreased 11 times).

I'm proud to present my newest build, which took me almost half a year: Grandfather clock with 19 different functions, possibly the most complicated Lego clock in the world. 20240210_133209 by David_Z1, on Flickr Standing almost 2 meters tall, this pendulum clock was an engineering challenge on multiple aspects, but the biggest problem was how to power all 19 functions and how to handle a highly variable friction produced by them. The answer was to use several electric motors triggered at the right time. There's no electronics, just mechanical contacts. Escapement - the central part of the clock that powers the pendulum, is powered by a small dropping weight that is frequently lifted back up by electric motor. This ensures a very steady input power, and thus good accuracy; the mean error is less than 3 minutes/day (after a day of working, it is off by less than 3 minutes). This is possible due to the use of John Harrison's grasshopper escapement, which is the most accurate type of pendulum clock mechanism. The electrical system is based on custom DC motors fitted with RCA plugs: 20240210_163033 by David_Z1, on Flickr Above You can also see the Westminster chime mechanism - at every quarter, it plays a melody like Big Ben. The chimes are made from aluminium pipes, 70-110 cm long, length tuned to specific musical notes. Here's the list of functions: Schem_front by David_Z1, on Flickr Schem_back by David_Z1, on Flickr And here a video demonstrating all of them:

Thank you!

I have the CADA orrery. Instructions indeed had some minor issues. Specifically the order some pieces are added seemed a little random at times and not like a sensible person would do. As if the instruction creation was at least partially automated.

90 m/s is very impressive! In fact, this may be one of the fastest shooting Lego thing ever. How did you measure the speed? With a chronograph?

I think that in the instructions, only the earth axis is lined up more or less properly, with proper seasons and equinoxes. I haven't checked but I believe that the initial moon position was whatever. In general, the set would benefit from some slip clutches allowing for easy correction of the relative positions.

One error in my previous post: everything is sidereal (rotations relative to fixed base), moon too. This means that we need the sidereal lunar month which is 27.32 days. So 27 is remarkably accurate after all! Now if we want some serious accuracy, I've done some more calculations and here are the results: calculations by David_Z1, on Flickr

Actually, I did XD In fairness, it is quite a bit more convoluted and makes use of multiple differentials, but for me that's a plus. The, moon is the most puzzling - a simple 1:28 would be better. I'l definitely make a mod implementing better gear ratios & limiting the color vomit on the model.

I got the set. Very pleasant build. Unfortunately, my Earth prints are also slightly displaced, Africa experienced catastrophic tectonic shift. After studying the gearing, I can confirm the earlier findings about gear ratios: 1 lunar month = 27 days (should be 29.53059 solar days) 1 sun rotation = 27 days (technically OK, some parts of the sun rotate at this speed) 1 hand crank rotation = 3 days Regarding the year, earth is atached in such a way that without input, it will remain stationary in relation to the base (not the arm). So it will gain an extra solar day throughout the year (from the perspective of earth, sun will do 1 full rotation). This means that the year length is 364.5 sidereal days (2:729 gear ratio, rotations in relation to fixed base/stars) + 1 solar day. Since the earth rotations are in relation to the fixed base, all the days in calculations are sidereal days, which are shorter than solar days (they are 23 hours, 56 minutes long, so approx. 0.997222 of a solar day). Therefore, the final periods, in solar days, are: 1 lunar month = 26.9249 days (should be 29.53059 days) 1 year = 364.4874 days (should be 365.2425 days) In short, year length is a little worse than the earlier calculations.

This one is truly jaw-dropping. Absolutely brilliant engineering.

A working calendar. The first obstacle was devising way to encode the length of the months. My "eureka" moment was using a days dial with 32 positions and a hand that skips 1-5 days at the end depending on the month. A 12-sided cam with 5 possible heights turned out to be quite doable and compact.

Amazing!

Indeed, the orbit eccentricity of Earth is less than 2% so including that would be just extra complexity with no visible difference. For moon, on the other hand, it would make more sense to add eccentricity, which is not that complicated mechanically. The comment about inaccurate sun size was hilarious; it should be about 100 times bigger than earth, good luck doing that (still simpler than realistic distances, would be a few kilometer radius lol).

Ok, here's a decently working stepper mechanism with 8t gear, now properly aligned with beams: I'm not 100% satisfied with the reliability, but the idea seems viable.

Yes, I understand, valid point. I'll try a few things tomorrow.

Here's my quick and dirty prototype. Works just fine in one direction, adding second pallet below is problematic.

I wonder if it's possible to build something like this but with 8t gear. Did some experiments, I could do a single direction stepper no problem, but two-directional one eludes me. Also, rubber connectors are great for replacing rubberbands when flexible components are needed.

I agree, IMO it is a technic set, and one of the better ones recently. I'm working on a motorized version right now, although wing flapping takes a lot of power; that's why regular helicopters are somewhat more practical :P