Hello.

I'd like to show you my 3d-printed puzzle, 'The Gear Megaminx'

I used to place a lot of pictures in post, So I think I have to split the post into several parts.

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| Overview
[Edge : 35mm, SLS-Nylon, Non-polished, partially dyed(Rit-golden yellow), printed by Wenext at Craftcloud(All3DP)]

Gear Megaminx is a Megaminx-based puzzle with dynamic gears and golden frames.
Actually, This is my first (partially)dyed puzzle with Rit-Dye.
you can also see this on My YouTube channel.

In Megaminx, the gear systems that can be established are quite limited, especially if there's the edge gear like geard 333.
In my puzzle, I avoided that problem by adding the center gear in addition to the edge and turning-face gears.
Actually, It has the same gear system as Michael's Gear Icosaminx, but different in gear ratio.

The gear ratio is 6:10:20, and there's no 'extra tooth' due to the size of the gear.
Because of that, this puzzle somewhat differs in its dynamic characteristics from ordinary gear puzzles.
Simply, there is 'Skip' in gear rotation. In particular, as the gear size problem, 'Bump' and 'Collision' also exist in my puzzle.*
(*This will be discussed in the following post.)

The puzzle has printed in SLS-Nylon ordered from Wenext(at CraftCloud(All3DP)) which is a Chinese company, not i.materialised.
The price(66.2$) is about 1/3 than i.m's(187.23€), and the quality is pretty good.

Finally, this puzzle was made using the 3D Gear generator which I made.

More details on the puzzle and design modifications follow below.

| Puzzle Making
As already mentioned, the puzzle was SLS-Nylon printed by Wenext at Craftcloud*.
The price(66.2$) is about 1/3 than i.m's(187.23€), so it's definitely less expensive.

(*Craftloud is a kind of intermediary for printing companies. Therefore, it is possible to compare the printing options of several companies on the webpage.)


This is the first time with this company, and the product was delivered without the sinterbox. In fact, the company wanted the walls of the sinterbox to be at least 1.5*1.5mm^2. So I had to send in a new file, and I told the company that the sinterbox was not important.

Perhaps that's why there is no sinterbox. Instead, the company sent me a photo of the piece being inspected. '31'is just my mistake lol.

I was a little worried because it is not an already verified company like i.m, but I am very satisfied with the result. This is not i.m's products but I think the hardness and strength were similar to those of i.m.

(Actually. I had to cut or polish this due to design mistake. And, of course, i.m's quality might be better due to higher cost)


This puzzle does not fix the center gear & the center piece & core at once for the normal rotation of the gear. Instead, the center piece is fixed indirectly from the corner with springs.

As a result, a total of 60 screws(M3, M2), and 40~50 M2 washers were used. In other words, its size is just a dodecahedron with an edge length of 35mm, but the perceived weight is similar to the MF8 9cm Dedecahedron series.

The assembly difficulty is quite high because of the many screws, gears, and the frames. Fortunately, assembly was well done thanks to the springs.



| The Movement of The Gear The initial design was the same as the one on the left of the picture, But this had little space to grap to turn.
That's why there's 'frame'. It wasn't intentional, but I think it's somewhat pretty.

Anyway, In this design, the extra tooth is only present in the center. So there are not enough extra tooth. In other words, this puzzle does not have the proper Rack Gear. (Generally, the rotating surface of the puzzle becomes a rack gear with extra teeth and other parts.)

Therefore, the edge gear really does not rotate(Skip) where there isn't rack gear and the rotation appears to be 'delayed'. As the result, This puzzle has the blocking like picture above.

Because of this, I had to remove all the extra teeth in the center and change the gear phase. Although the phase has been shifted, there is still interference between the edge gears.(Bump and Collision)

More precisely, it works like this picture. Not only do the gears bump into each other, but they even collide.

With a regular 6:10:20 gear ratio, the gear should rotate by '4 theeth' per 72º of megaminx turn. However, due to the absence of the rack gear, it only rotates by '2'. But all gears in this puzzle actually rotate by '3' (180º) due to the 'Bump. It's really weird.

Even though there is collision, the puzzle works somewhat well like video and gif. That's because the collision is not too serious(0.5~1mm) and the gears are slightly misaligned to avoid collision. However, this cause misalignment of the overall gear system. As a result, it is better to modify the design.

So there are two solution. The one is trim the gears to eliminate collisions, and the other one is changing the gear size to make extra teeth which are needed to avoid skip and delay.

Actually, the total size of the gear decreases when the pressure angle of the gear increases. Changing the actual size(pitch circle) causes the bad gear ratio, so changing the pressure angle is much better.

If I move to the phase here again, I think I could make the appropriate extra tooth.

| Design Improvement

Thus, the revised design looks like this: By changing the pressure angle from 20º to 29.44º, the size of the gear became smaller and it was possible to make extra tooth. If Using 30º as the pressure angle, the tooth profiles of the edge gears overlap each other, causing the gears to smaller more than necessary. (This is checked with my gear generator tool.)

All modifications are done now, but I have not been printed yet.
If you are interested, you can download the file from My google Drive Link.

The parts used together are as follows.
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M3_12mm+_20EA (Inner center)
M2_8mm~11mm_30EA (Edge)
M2_12~16mm_12EA (Center)
Spring_20EA (Inner center_must be used)
M2 washers are optional.

Spring = [h=7.5mm, Φ=5mm, wire thickness : 0.5mm, k=1.687N/mm]
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This is my second post, but it seems too long.

Anyway, thank you all.

What a cool puzzle! Thank you for the detailed writeup, and for the tip about CraftCloud.

Also, don't worry about long posts! It's always good to see another puzzler's process!

Eitan

Excellent post, too long is not long enough! Great puzzle, I look forward to more of your designs.

Impressive!

Very nice looking design. Thanks for all the details.

Carl