A friend (Malcolm, internet name "Bluhr") and I are developing this into a controller for index-style singles and doubles play. This video shows some patterns you could do on a setup like this that you might not be able to do on index, and how this setup is much more comfortable than index.
The basic idea is this:
1. Even though the perceived distance between pop'n buttons and keyboard keys is much greater, the muscular exertion required to move across pop'n buttons vs. an index setup is surprisingly equivalent. However, fast movements on pop'n buttons look much more entertaining to watch and feel much more satisfying.
2. Index doubles is not a thing, but could be, since doubles is enabled by default in 3.9, and the pattern potential is massive.
3. While it is true that something like this:

(credit: Carlos / Wayward Vagabond)
Would allow for far more natural movements across eight keys, we chose two DDR-style setups for doubles because
(a) most people are already familiar with this format, both in terms of play and stepfile design
(b) this allows for direct carryover from DDR/ITG doubles charts, as well as mild carryover from IIDX/solo charts
(c) this allows for 4-button singles, while the above setup only works for 8-button singles
(d) this allows for 2-player, which the above also does not
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So, with that said, the circles in the video are a little bit smaller than they should be. They're about 82.5mm and we'll be using 100mm buttons. However, I think the 100mm diameter includes the outside rim, so the button itself might be about 85 or 90mm -- not a huge difference, really, but slightly noticeable.
These are the dome buttons we're using. Economy buttons are available, but I've read reviews and have heard that they rattle, which is not something you want when you're doing 16th stream at 240+ bpm, so I'm opting for the same buttons used in pop'n controllers which I know for a fact are durable.
We are negotiating how to do start/exit/movement buttons. Something like this might be good, but since navigation buttons would not need to adhere to nearly the same durability standards as the dome buttons, we could use these
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Side note: if there is enough interest in this, we might be able to make extra to sell to all of you. I have no idea what the price would be, and it would depend on how much labor is involved. We could also make 4-button controllers if you just want to play singles. (Shipping internationally wouldn't be a problem, but obviously it's going to cost a lot more.)
I have used both Ransai and official Konami Pop'n Music ASC controllers before. Ransai controllers do not have a comfortable distance between buttons -- they're farther apart than the buttons on the official Pop'n Music arcade machine. Also, both the Ransai and Konami ASC are extremely noisy, and have to be padded to reduce noise. Both of us live in houses where we stay up late while other people sleep, so we're conscious of noise and will make sure that there is none.
That's about it so far. Let me know what you think.















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