Book IV Prelude Challenge: Category A: The Astral Obscurvatory

[Yoggington]

<- Reserving this post for the final product ->

[Yoggington]

 <March 16th> 

I'm not sure if I should start a separate thread, just pop updates in here, or maybe even not post at all until the gate-point. I figure I'll hold myself to account and keep myself honest by posting in here if I make anything I could think of as progress. Spoiler tags as this is quite image-heavy.

I have for a while wanted to tackle an observatory, specifically one with a nice dome on it. Something not too modern or sleek - along the lines of the Dominion Observatory. But of course, domes are rather tricky to pull off in lego. Looking at this technique, while of course it could be used for the tower .. if I flipped it over sideways, and with a little modification - maybe it could be used for a dome?

I started with a circular floor:

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Then while struggling with filling in the gaps, decided it was way too big anyway. I messed around with a variety of smaller circular shapes, but not many of them would take a snug ring of rounded plates on the perimeter. I found to my delight that just mimicing the pagoda base from Rivendell gave something just the right size.

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It does have an odd stud count to divide to 6 or 8, but if you add a few 3-plates, it works out with odd sized sections (which I kinda wanted anyway)

 

This is not a dome! I hear you say. Yes, Rollo knows his shapes. So far, we only have a circle-ish.

My hope is to add flexible rods something like this:

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And then connect them in the centre something like this: 

 

You will be left with bendy-pizza-slice sections you can then fill up using the technique in the thread :)

I gave that a bit of a go, and found it all entirely unreliable. Looking back at my reference pics, I noticed that observatories aren't even dome shaped!! They have a smooth half cylinder in the centre, and then a half-dome to each side. That smooth part is the bit you see opening and closing sometimes. It also might be a little easier to try out.

I ended up with this: 

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Inners: 

 

Next stop, bendy pizza slices.

[Grover]

I love the name!  I don't have a lot of commentary beyond what I posted previously, but congrats, you are the second member to make the WIP midpoint deadline, and the only one eligible for prizes at this point! 

[Yoggington]

Well, there wasn't a whole lot of update in that update. However, I created the thread because another one is incoming! The update is that bendy pizza slices are easier said than done.

Firstly, I had a mad idea that maybe I could have this whole dome rotate on gears atop the tower. I don't know if I'll go that far with this iteration (let's maybe build a tower first), but I know if I do end up going down that route, I need a more solid unit. I found that sheer friction was not enough to hold the ring around the base, and the whole thing kept sliding a little - so I needed to create some connection points. Not so easy with the way the Rivendell base is made. I rejigged the whole thing. The diameter is the same as previously, but now it is five plates thick, and has the necessary connection points. Only two, because of how the odd/even stud count works on the ring.

This was a lot more complicated than I'd like, mostly due to the odd stud count width (7 up to 11). However, that same odd stud count allowed for a pleasing floor pattern to work just right with the 'corners' of the disc.

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As part of this, I've changed the rafters to be eight groups instead of six. While prototyping, I found these panels were far too wide to be reliable with the y-axis curve, so slimmer sections means they can be flat crossways.

I am quite proud of how I've put the butt of each rafter together. Towards the inner, you need two rafters, one for each side panel to grab a hold of - and two so that they don't interfere with each other. And then you have a third toward the outer - this allows an outer 'rafter' that will somewhat hide the seam between the panels.

Spoiler

 

So far so aesthetic. However, the cleverness comes because the round 2x2 that supports the outer rafter also doubles as a stopper for the internal rafters. The flex tube for these goes through the stud holes in the round 1x2, but stops when it hits the solid studs of the 2x2 - meaning you get exact heights where previously it was a lot of guess-timation.

Up top we have a technic spiderweb to keep the whole thing in place. That took a bit of consideration. The build is quite firm at this point. Still got a bit of give, but firm. I have some radar pieces in sand green that will eventually cap this off. I would like a 10x10 dish, but there are only 10 available on all of Bricklink (and priced accordingly).
 

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One good thing about building as slowly as I am able to, is that by the time a Bricklink order arrives, I probably haven't yet had another build session anyway 

The panels. 

This is what is causing me the most grief right now. I laid out a nice set-up that worked decently well, very few gaps and pretty solid. Ordered the missing pieces in the colours I'm going for. Rebuilt it... and now they no longer fit as they did on the prototype. Dropping my buttress stopper pieces by one plate (when I moved from six to eight) changed the shape of the dome  Now four of them ping off at the slightest touch, so I have to rethink their shape and connection. 
 

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What might work better is what you see here in the left and right panels. I've connected them top to bottom with a flex tube (the gold one sticking up), which pulls the whole thing to a far more solid place.

 

What I do like is that I've managed to keep it pretty clean inside too, so if you peer in the gap where the telescope will look out, it is not a mess of supports.

 

Now, next step is to stop faffing about with the roof, and get some bulk work done on the body of the tower.

I've had an idea, as the inside of the tower is not going to be very accessible (unless, hmm..) - to put a staircase on the outside - give it all a bit more area to place figs, make the silhouette more interesting than just a cylinder. With the walls being built using the tutorial method, we'll have studs facing outwards anyway. That should make it possible to build a stair sideways. 

 

[The Stad]

I really appreciate seeing your thought process in pictures and reading your trial-and-error commentary alongside it all.  I'm excited to see your final product!

I know it's tough working with a system as rigid as Lego, so there will always be inherent limitations to the shapes that can be achieved, but my impression right now is that your roof seems very conical, rather than domed.  I don't know that there is any reason why it needs to be domed, but it does seem like a departure from the classical look of an observatory.  Maybe there's a story reason for that though...

[Yoggington]

On 4/23/2026 at 6:09 PM, The Stad said:

I really appreciate seeing your thought process in pictures and reading your trial-and-error commentary alongside it all.  I'm excited to see your final product!

I know it's tough working with a system as rigid as Lego, so there will always be inherent limitations to the shapes that can be achieved, but my impression right now is that your roof seems very conical, rather than domed.  I don't know that there is any reason why it needs to be domed, but it does seem like a departure from the classical look of an observatory.  Maybe there's a story reason for that though...

You are not wrong, it's very cone-ey instead of domey. I haven't posted any pics with the capstone in place, but it does slightly reduce the issue. (We go from cone to severed cone  ). 

If I want to keep it minifig scale, I think the fix would involve making the base much wider - which I'm not going to do at this stage. So I'll say yes, there's a story reason. Such is the whimsy of Avalonia.

[T-86(swebrickLUG)]

Super fun following your progress both in text and photos. Keep it up, Im looking forward to see how you handle your dome and how it ends up! Let the whimsy of Avalonia continue 👍😃

[Seagull King of Vaughan]

I’m very impressed by this idea, as a dome seems quite challenging to complete. It looks very nice! Sand green is just as good a colour as sand blue.

[Grover]

On 4/23/2026 at 4:52 AM, Yoggington said:

Well, there wasn't a whole lot of update in that update. However, I created the thread because another one is incoming! The update is that bendy pizza slices are easier said than done.

You have taken on a challenging project, that is for sure!  It took me a bit to get back to you because I wanted to take a picture of something that might help (see below).

On 4/23/2026 at 4:52 AM, Yoggington said:

he diameter is the same as previously, but now it is five plates thick, and has the necessary connection points. Only two, because of how the odd/even stud count works on the ring.

This is a trick, isn't it?  Glad you're using a round base as a sort of jig to get this round. For anyone reading, if you want a circular shape, a form or jig can really help.  And you have found one of the main tricks, which is that gridded studs don't line up well on a circle!  I like how you have 2 connection points built in to your circle to add structural integrity.

On 4/23/2026 at 4:52 AM, Yoggington said:

While prototyping, I found these panels were far too wide to be reliable with the y-axis curve, so slimmer sections means they can be flat crossways.

Generally, the more parts you have, the less pixellated you get with this technique, and it allows for flat (rather than sloped or curved) panels. This means more degrees of freedom in building, so although it may seem backwards, it can actually be better to have more smaller flat pieces than fewer larger curved ones.

On 4/23/2026 at 4:52 AM, Yoggington said:

I am quite proud of how I've put the butt of each rafter together. Towards the inner, you need two rafters, one for each side panel to grab a hold of - and two so that they don't interfere with each other. And then you have a third toward the outer - this allows an outer 'rafter' that will somewhat hide the seam between the panels.

This is very much the difficulty here.  One of the issues is that you're using the track from this technique to form the bottom round base not as a track, but as an actual building plate. Maximum movement would put a flexible stick on this and curve it to the top. However, you want the tracks going in all 3 dimensions, and the only parts available to do this are the flex tubes and the 1x1 cylinders that you have used.  This requires there to be two sets of the curved tracks as you have found, and that makes covering the track with the stick impossible.  The base technique uses the fact that 2 studs horizontal equals 5 plates vertical. In your case, you have 1 stud horizontal and 1 stud vertical covering on each end with a bend in the middle.  In this case, you have made an external arch to cover the gap, which works with your build. If you didn't want that, you might be able to add another layer of plates to the roofing and then interleave overlapping plates or even 1x2 curved slopes to cover the gap.

On 4/23/2026 at 4:52 AM, Yoggington said:

So far so aesthetic. However, the cleverness comes because the round 2x2 that supports the outer rafter also doubles as a stopper for the internal rafters. The flex tube for these goes through the stud holes in the round 1x2, but stops when it hits the solid studs of the 2x2 - meaning you get exact heights where previously it was a lot of guess-timation.

That part is true, but you also lose the infinite movement of the stick on tracks, limiting your spacing to the studs, which can create gaps. I'm sure it's more structurally sound, and that might be a consideration with something this detailed.

On 4/23/2026 at 4:52 AM, Yoggington said:

Up top we have a technic spiderweb to keep the whole thing in place.

Here is where I had a thought for you. Rather than force your build into the 8 sided technic piece, what about making it infinitely moveable with a large steering wheel (#67811) and adding the clips with some tubing (approximated here by bright green bars) attached so you can slide them wherever you want?

In this way, you can move the flexible tracks with your cylinders to exact positions and smooth it out a bit.

On 4/23/2026 at 4:52 AM, Yoggington said:

The panels. 

This is what is causing me the most grief right now.

As I mentioned before, more smaller parts can have advantages over fewer larger ones. In your case, at the bottom of the dome, you could have a few 1x5 sticks that rest on the dome curve, rather than the 3x5 plate that is there now. The real benefit of this technique is that you *don't* have to use hinges or large plates and by adding some 1x2 (or 2x2 etc.) tiles or plates to the sticks, you can interleave them and create a rounded effect. In your case, using three 1x5 horizontal sticks with 1x2 sand green tiles interleaving between them may give you more of the effect you want. This would become problematic when you shrunk the next layer up as a 1x4 stick since the studs would not line up for interleaving, but you might be able to layer at that point (see below).

Another option might be to have an overlap, where each progressive level that goes up the dome has a layer of tiles that overlaps the first like roof singles. Then successive smaller sticks as the dome climbs would be able to layer without needing studs to line up.  Of course, these are ideas that might be easier said than done given the small space you have, but I'm hoping these might give you a few more ideas of things to try.

Overall, this is a very impressive and challenging piece. It's great that you're showing a lot of the WIP here, both the things that worked out and those that didn't. That helps drive new ideas and creativity here!  Keep up the great work!

[Yoggington]

On 5/2/2026 at 7:24 PM, Grover said:

Here is where I had a thought for you. Rather than force your build into the 8 sided technic piece, what about making it infinitely moveable with a large steering wheel (#67811) and adding the clips with some tubing (approximated here by bright green bars) attached so you can slide them wherever you want?/

In this way, you can move the flexible tracks with your cylinders to exact positions and smooth it out a bit.

This is actually how the 'outer rafters' connect - I realise I haven't actually taken a picture of that part. Well, it's close to this, there are actually two rings side by side.

I will look into the idea of smaller sections instead of larger. It feels counter-intuitive, although I can see the logic now that you've typed it out.

Really I need to plough on with the tower body, I could spend months perfecting the dome quickly enough.

[Yoggington]

The dome can wait!

I do need to get a start on a tower body. Get the bulk out of the way so I can get lost in the details later.

I've landed on a circle width, about as in-system as I could have hoped for. Starting with a smaller 'banana' gear, Ive wrapped another ring of the glorious rounded 1x2s around it, and found they link up nicely once wrapped (not true for many other sizes I tried). Something I didn't know, is that the quadrants of this gear are each exactly eight studs apart (or close enough that I can't tell without going digital). I'm sure there is good reason for that, but the math of circles always throws me for a loop  Note the green studs below.

With a defined centre lining up to the edges, this means I can secure it to a baseplate with relative ease, and if I go with modular sections, can stack them later too. It also leaves the option open to have a rotating dome in the future.
 

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I've then gone with the expected technique, but there are two advantages to using this exact diameter.

Firstly, by double-stacking the plates on the inside of the tower, they all very neatly just about close up all the gaps. Secondly on the outside, you can see that is 4/2/4/2 configuration with slopes included, means you get a very neat brickwork pattern that again, practically closes the gaps.

I am pretty sure I've seen this before, maybe on a pot in the botanical range, and I've probably gone a very long way around to the same end-result, but I feel the achievement of discovering it myself at least.
 

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A few future thoughts:
 

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By inserting a matching ring of 1x2s at the top, the whole thing is very sturdy altogether, even once disconnected.

It has a very pleasing diameter when compared to the dome, just a step slimmer.

And lastly, I have started to mull over the possibility of external stairs. Because the outside is made up of 14 panels, a side-built stairs gets halfway round the tower in 8, which is again, a very pleasing amount proportionally.

 

Obviously we'll go taller then eight studs (unless it's just poking out of the clouds?), but importantly this design is very scalable.

I think my next step is to decide just how tall this will eventually be, and look into doors and windows placements based on that. I've a few ideas there already.

Edited 2 hours ago by Yoggington