Designing a Lego orrery | Hacker News Reader

Designing a Lego orrery

marian42.de

622 points_Microft65 comments

The author spends lots of time modelling axial tilt to represent the seasons.

Then there was this gem:

> I also used this program to create digital building instructions. My takeaway from this is that it works really well for small models, but it has serious usability problems on larger models. When you make changes to the model or change an early step in the instructions, it will often break the layout of the instructions in many places so that most of it needs to be redone. This was a lot of tedious work, but I ended up with a 264 page, 436 step instructions PDF.

Wow.

That actually doesn’t seem that bad for a model this complex. The larger sets can have well into the hundreds of steps with manuals reaching into several hundred pages on 8x10 paper.

I used a Lego product this past week and the instructions were actually omitting 1-2 steps explicitly and expecting you to see the difference between the current and previous figures in the print.

In the old days, "spot the difference" was the standard practice in Lego instructions [0]

0: https://www.toysperiod.com/download.php?file=h4d4k5w544a4h4n...

As it should be. I credit LEGO for my acing the ASVAB spatial reasoning sections.

About an hour after reading this blog post and the thread here on HN, I opened Instagram. The very first ad was from Lego, for their orrery.

It was so specific and unique (I can’t recall ever seeing an ad from Lego on IG at all) that it must have been targeted by some behavioral data on me.

But from where? HN and the blog do not seem to be running the Meta pixel, and I was using Safari on iOS, which blocks 3rd party cookies.

After some recollection, I remembered that I had clicked play on one of the YouTube videos that are embedded in the blog post. So Lego must have Google ads running that target people who view these orrery project videos.

Do you even need to click play on a video, or is the act of loading the embed enough?

EFF's Privacy Badger shows a few potential trackers when loading that page.

https://github.com/EFForg/privacybadger

Whenever I see a project like this that involves hundreds of hours of engineering and craftsmanship, I think: Doing nothing after retirement doesn't appeal to me, so this is how I'd love to spend my time (even sooner if circumstances allow).

What do you think retirement is?

That's retirement.

Retirement = you bought (pension/savings/investments) yourself time in your 20-30 last years in life to enjoy. You are paying yourself to do what pleases you.

You paid everyone in life first. Now you pay yourself. Last.

Naturally. Retirement is the most expensive thing you'll ever buy!

I just wish that I'll be healthy when I retire

The picture at the start of the article just says it all. I was just looking at it for minutes and didn't dare to scroll down.

Embracing your passion for craftsmanship now

> To make matters worse, the axis always points in the same direction.

I don't understand how this was never explained to me in high school. Of course we learned that the tilt of Earth is what causes seasons, but I never understood why. Now I know why I didn't understand it, some part was missing.

And I literally thought I wasn't smart enough to understand.

It follows from conservation of angular momentum :) If the axis direction changed (for a fixed orbit), then Earth's (or Solar system's, etc.) angular momentum would be changed, not be conserved.

Unless the Sun's tilt moved ever so slightly in compensation.

Around one one billionth of a degree to be exact. Impossible to detect.

Indeed. Another fact you can use is that in Newtonian mechanics (although not in GR due to frame dragging, only approximately), a rotating spherical body has the same gravitational field as a static one. So there would be no mechanism for the axially tilted rotating Earth to influence the Sun (different from a non-rotating Earth).

I guess a good animated 3d model, either digitally or one you can touch like this orrery, would have cleared up a lot of confusion. Especially if you can play with it in a darkened room with a flashlight.

Yeah, the critical insight is that the tilt impacts how high in the sky the sun is, which in turn affects the length of the day and the incidence angle of the sunlight.

You do not need a complex 3d model, very simple illustrations show it well.

https://kidspressmagazine.com/wp-content/uploads/2014/04/dre...

And then explaining that the hemisphere that receives the sun energy perpendicularly get more heat from it.

https://scitechdaily.com/images/Earths-Seasons-Tilt-scaled.j...

I'm not sure about 'complex'. Something three-dimensional that you can interact with often help people's intuition more and more quickly than a 2d static illustration.

I know how the season's work, so I find the illustrations you linked to clear. But OptionOfT complained that they never understood the explanation in high school (and that looking at the lego model was enough), and presumably they had at least a static 2d illustration in the text book.

(For example your second link https://scitechdaily.com/images/Earths-Seasons-Tilt-scaled.j... doesn't really make clear that the angle between earth's axis (pointing north) and direction between earth-and-sun change throughout the year.

Your first link tries to make that a bit clearer, but it's still hard to interpret, if you don't already understand the mechanism.)

It does rotate, but it's slow enought to not matter in most cases. Afaik some ancient, star aligned constructions do not work anymore because of this

https://en.m.wikipedia.org/wiki/Axial_precession

The thing I spent some time puzzling about recently is why the changes to sunrise and sunset times through the year aren't symmetric about midday and why they have different rates at different time of the year. This led me to the equation of time [0], another fascinating rabbit hole.

[0] https://en.wikipedia.org/wiki/Equation_of_time

I noticed this often happens in school. A key piece of information is just missing and you just learn the right answer to pas tests, but never know why

It has some benefits. Some can be pushed to seek explanations beyond the surface level

They used to tell us you could stand an egg on its end on the equinox because the Earth was standing straight up and down. It really wasn't part of class, just something people mentioned. I even remember seeing a short news story of kids actually trying it in school. Then at one point one of my teachers pointed out people figured out you could do it any day of the year.

The gear ratio calculator is great and will be of great use! Thanks!

Extra + for making the form variables controllable by URL params: https://marian42.de/gears/?targetratio=2/8&dst=any&gears=def...

The project is open source: https://github.com/marian42/gears

The creator of this also made a tool to design custom, 3d-printable Lego-compatible pieces:

https://marian42.de/article/partdesigner/

Now if only we can reliably 3D print the gears also, and ensure they still work well with other pieces.

This is so awesome. There’s a lot to geek out about here, but I was personally enamored with the extra effort to make good renders/visualizations in software. Thanks for the read!

I have the not-Lego™ orrery he mentioned at the start and it is great. Very good value for money & fun to build. It is sad that you can't use it to explain seasons though, like you can with his serious upgrade. Nice work!

Great article! I would also highly recommending following the link at the end for the video on Akiyuki's clock [0]. It's a masterpiece, and that's saying something for how brilliant his other designs are.

0: https://www.youtube.com/watch?v=GUdlSYC1cCE

I too am disappointed by the direction Lego has gone away from the classic Technic gears and pulleys. And the cancellation of Mindstorms without an adequate replacement. It’s the end of an era. Now everything is mostly focused on brand deals with all the popular themed kids toys.

What about wedo and spike? I think they look pretty ok…

Well, "pretty ok" is not a great bar coming from the mindstorms system. But even if you exclude that entire category, the Technic series overall is not the same as it used to be.

Art is often enhanced by the constraints of the medium in which it is realized.

wow thats cool. Lego should pay him lots of money for the plan and sella few kits of it.

As he mentions in the article, LEGO does sell a kit already, set 42179. I find it unlikely they'll adopt his design when they already sell one of their own, even if his has improvements that he mentions.

Though it looks like it's not strictly against https://ideas.lego.com/guidelines , under "PLEASE ONLY SUGGEST NEW IDEAS. NO IDEAS TO “BRING BACK” OLD LEGO SETS." they say:

> Don’t submit product ideas requesting we re-release or “bring back” discontinued LEGO products or themes in their original form, and don’t submit product ideas that are “modifications,” “improvements,” or “expansion sets” to existing or past LEGO sets. If you’re submitting a product idea based on a discontinued LEGO theme or brand (for example Blacktron or Octan), it must be your own new, creative work.

simply because this design predates the official re-release... but given that the official one is from this year, it seems really unlikely they'd run with it this soon anyway.

This is great, also the various calculators and parts designer.

I've been looking to build an articulated clock, which is pretty much an orrery like this but without planets and different gear ratios.

Difficulty is that I'd like to have the second hand keep straight from minute hand at whole minutes. And I think I need a gear ratio of 61 for that. Or Keep it straight up at whole minutes, which needs a gear ratio of 59 IIRC. Both primes, so not easily achievable with gears.

It's been a while since I spent time on this though.

EDIT: I could add/subtract 1 rotation via a differential gear I think.

One of those examples where a community creation is miles better than the "official" Lego design.

Better by some measure - LEGO is probably optimizing for different metrics:

- Number of distinct pieces (fewer is better),

- Complexity of build-process,

- Robustness,

They make a model of this exact thing: https://www.lego.com/en-us/product/planet-earth-and-moon-in-...

The author describes their experience with this set

> Two years later in 2024, Lego released their own orrey design. I was quite excited at the prospect of an official Lego orrery, but I was disappointed by the execution....

The lego one is actually pretty nice, and cheaper than most ready-made models.

The one part that isn't quite right, and I'm not even sure I've ever seen a model that does this right, is the moon's orbital tilt, so the earth isn't blocking the moon for full moon, and the moon isn't blocking the sun for new moon. The distances probably don't scale to make it practical, the tilt would have to be extremely exaggerated. The phases of the moon is the only thing that I've never seen an orrery show very well.

Daaaaaang that’s amazing.

I want to build this as the first bit of a clock like the one in Anathem.

Schools should teach Lego and such mechanics in particular as mandatory classes. Starting from first year with increasing complexity. Of course alongside classes for graph networks and their applications.

Counterpoint (from the perspective of a science teacher who has used LEGO as part of teaching, and who still has about 70 pounds of LEGO): LEGO pieces reinforce "blocky" engineer mindset, reinforcing the idea that we can "fix" climate change with technology.

We're up against a population boom enabled by access to fossil fuels. Our nigh-insatiable appetite for energy conversion has serious consequences for life on earth.

I'd far rather teach basketry & other fiber arts, foraging for food & medicine, land stewardship, how to hunt kill and process animals for food, and other primitive (using this word non-pejoratively) skills done as a tight-knot group (such as what a classroom can be with good leadership- not saying I provided that to the degree I value now, but if/when I go back to teaching, I will). LEGO is a distraction, a luxury enabled by the Industrial Revolution. We don't have plastic interlocking bricks without coal and petroleum and long (and easily-disrupted) supply chain.

Until a few years ago my LEGO collection, amassed in childhood, was a prized possession. Now I'd have sold it or given it away were it not for my wife advising we keep it for our child. In light of what I wrote above, while I can get down on the ground and immerse myself in creative parallel play, I'll also promote the old ways to plant the seeds of a wonderful, effortful, meaningful life that also has a more down-to-earth carbon footprint.

Climate change is not a reason to not enjoy Legos. Life is for enjoying, not for worrying about whether one's hobby is environmentally friendly enough.

This brings me back to young me and my mechanic dad making a hydraulic car with Lego Technic. Isn't Lego just the best, for all ages and all walks of life?

See also this older LEGO orrery produced by the University of California as an educational project for NASA Kepler mission:

https://www.nasa.gov/wp-content/uploads/2016/09/table-top_tr... https://www.nasa.gov/wp-content/uploads/2016/09/table-top_tr...

Also: http://mrob.com/pub/lego/orrery.html

I love Legos, I usually make them and give them away. Now, this one surprised me and I was amazed. I will never do this, but WOW!!!!

The is wonderful

This is lame, the world needs smart people like you solving real problems. A cool project but dumb as hell at the same time.

How many smart people run marathons, do all night drink binging sessions, travel to exotic cities and other such follies?

My belief is that a project like this (and probably the marathon and travel too!) make you smarter. You need to do something that ain’t work sometimes!

Ignoring most of your comment and only focusing on this part:

> the world needs smart people like you solving real problems

It has them. And they’re doing pretty much exactly this. What’s described in the OP resembles a pretty standard machine design process – the key is splitting up the complex goal into smaller manageable units. (And using tools for the tedious parts such as gear math; if the tools don’t exist, you of course develop your own!)

The author was presumably able to do this because they’ve already solved a real problem or two.

it's a bit like Richard Fenyman's wobbling plate — you don't necessarily know where you'll end up (maybe with a Nobel prize).

— https://www.asc.ohio-state.edu/kilcup.1/262/feynman.html

How about a nice metal non-LEGO orrery that doesn't cost a gajillion dollars.

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