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Archive for July 28th, 2020

Southern Star Wheel

July 28th, 2020 by RoscoHead

The “Melbourne Star” is an observation wheel in Melbourne’s Docklands area, giving an unparalleled view of the city. So what’s that got to do with my Southern Star Wheel? I’m glad you asked!

The current wheel (bottom, incomplete) was built after problems were discovered with the original design (top). You can see the hub & spoke design is significantly different. So it was decided the new attraction needed a different name, so it wouldn’t be forever tarnished with the memory of the first failed version.

And that is why my MOC, based on the original design, is named “Southern Star”, rather than “Melbourne Star”. If you want to see a model of the “Melbourne Star”, check out The Brickman.

So much for introductions. As you can see, both wheels are based on the 7-point “Commonwealth Star” depicted on the lower hoist quarter of the flag of Australia. Six of the seven points represent the original six states of Australia, while the seventh represents the territories.

Anyway, that meant I had to come up with a way to create a symmetrical 7-point star using LEGO, which is not a trivial task. After many hours of trial and error, I came upon the approximation that

 sin(Ï€/14) = 2/9

And with that knowledge I was able to come up with a hub composed of 14 equal segments.

Once I had a solid hub, I needed 7 points. This I worked out by finding a point length that resulted in a circumference divisible by 21. This was because the circumference had to approximate a circle, and each section had to carry a single observation car, so it would be much easier if they were all the same length. It worked out that a circumference of 21 x 15 studs was almost perfect.

And next I needed to fit a section between each pair of points that resulted in approximately the correct angle between all 21 segments. This also proved to be more difficult than expected, but after lots of failed attempts, I eventually ended up with this.

Purists please ignore the thin plastic spacers I used in the centre join.

The ends are attached using longitudinal pins, attached via rubber mounts to allow some movement.

It’s starting to get pretty heavy now, so the next order of business is a strong mounting frame.

Each side has a vertical mast which supports most of the load, and 2 diagonal braces to hold it upright. Some tricky connections where the 3 come together at the top.

It’s all made to be assembled as easily as possible at shows.

On to the cars. The trickiest thing about these was that I wanted them to look as much like the real pods as possible, and they also had to rotate to remain vertical.

Purists again please ignore the plastic spacers used as washer to minimise friction.

The design I ended up with was actually too short for minifigs to have hair, so this wheel has the unusual restriction that riders must be bald!

The cars are attached using an axle connector at each end.

All we need now is a way to drive it. This is what I came up with (upside down!) – the main requirement was to have some pressure on the driving frame so it could maintain solid contact with the wheel which is not perfectly circular.

In the end, it is probably way more complex than it needed to be, and is definitely not as reliable as I’d like. But it generally works OK.

So in conclusion, there’s quite a few things I’d change if I was building it today:

  • The drive mechanism
  • The car design
  • The main frame joint

But I’m not, so I won’t.

And here’s the obligatory setup video, filmed in reverse & sped up 5x.

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