[23 Dec, 10:00]

Whilst I haven't been able to find any human-computer interface (Charachorder, TapXR, ...) or unique and repurposable musical instrument that has as much of a solution coverage as #Tetent TestCut (or #Tetent Timespy [gd0136] if looking for wearables), I'm still looking for ways to obtain a 14x17mm bounding cross section for Tetrinsic. The height of 14mm is more of a guideline where it would likely be worthwhile to do a full CAD remodel; not much point doing it if I'm only saving 1mm or so.

For starters, I thought about the loop path that I'd use if I ever did find a solution:

The dark grey is the loop and the light grey dots is the loop at a lower elevation. This allows the use of 1 long loop that can be tensioned, and means that the outer loop section doesn't have to be connected to the motor somehow.

The requirement of the loop was that it has to be able to transmit vibrations, as mentioned in the previous log.

I'm scrolling after hours of general research, about to pack up and move on, and I look at a ball-in-a-track solution one last time:I notice that the top of the track is covered, implying that the balls would just fall out if I tried having it more open to give the fingers more grip area. 

I then turned to ball chains one last time. The issue is that they have a large bead that connects the ends:However, in my Google Images search, I came across this:

and I'm like "Yes yes yes yes!" because I could use a semi-rigid loop that should be able to conduct haptic vibrations well, and I have more flexibility in chord lengths. That is, until I found out that the minimum size is 3.2mm. The motor is 11.1mm and the UMPE tape is 0.3mm. That leaves 2.6mm or so. Ok... fine, 14.5mm is probably decent enough to continue.

Now I'm on AliExpress.

It's nice to see that there indeed is a ball chain under 2.6mm and that they come in a variety of colours, unlike GT2 belts.

The only partial concerns I have are grip and potential corrosion if the chain isn't stainless steel. These concerns mean nothing though if I can't actually find an affordable clamp and suitable chain to use it with.

Cheapest I can find so far is £43

I found what looks to be an identical one for £60, but this one says that it works with 4.5mm ball chains which is a bit too large.

I also had a feeling that joining 2 differently coloured chains could be done to have some extra fancy effects when in use:

I still don't know what's with the markup though. It's bottom dollar on Alibaba:

[12:00] Ok I've watched some videos and this tool looks like a wire cutter, a sharp point press and a spherical mold press all in one. For now, I'm going to assume that it'll be possible to DIY a tool for 2.4mm or smaller balls considering that it currently looks like it doesn't exist (and it'll be £££ if it did).

[17:15] Ok. Suprisingly coincidentally, I got to touch a metal ball chain for like 60 seconds. The grip seemed fine and felt quite nice. 

This motivated me to visit an arts+craft store I've never been in before and they indeed had some ball chain. Unfortunately, they only had plastic, but they had it in a variety of sizes/colours so I could feel the differences and answer more questions like:

1. Can I still move the chain when only lightly pressing on it with Finger5? Yes
2. What is the ideal formation for balls across 2 rows? Square-like, as expected. The finger doesn't grip all that well in a triangular-like formation.
3. Could I have backlighting, getting another one for "Initial requirements" bingo? Yes. 
   1. The balls are much more see-through than GT2 belt, meaning that any underglow lighting would actually have a nice looking effect. 
   2. If I allow for additional thickness (15-17mm), I might be able to fit screens underneath. 
      1. Ideally I'd want Tetrinsic to cover as much of a solution as possible in one pass, and screens for live background effects similar to Flux Keyboard certainly have a very nice aesthetic. Aesthetic sells.
      2. A single block colour white LED is much simpler to implement though, and could look better than seeing an off-axis TFT panel. A turned-off TFT may also look worse on an all-white Tetent build.
4. Could I get by with just 1 ball chain column? Yes, but 2 feels more secure.