Well, testing has already uncovered a pretty big flaw with the rubber cap. After about 20 hours of mario 64 speedrunning the rubber on the cap split and started coming off, not good at all but I was half expecting it after what happened to Sanni's cap during shipping.
The silicone rubber (only 0.7mm thick on the early prototypes, now 1mm) when under tension is prone to splitting when something sharp or abrasive comes in contact over a period of time.
My style of play obviously doesn't have the same abrasive effect on the edge of the cap, all my rubber test sticks have been solid over a few months and I've been clocking up quite a few hours on MK recently.
So that's a pretty big fail, but glad it got caught in testing, back to the drawing board to see what I can do to make it more durable...
Any material experts out there have some suggestions for a more durable rubber compound to be used for the sleeve. Latex, neoprene, nitrile come to mind as alternatives but not sure if they would hold up better.
Here's the aftermath of the splitting incident.
I spent the day troubleshooting the rubber caps and seeing what caused the problem. I think I have a solution that works.
The new 1mm thick silicone rubber (clear sample I showed) is much sturdier than the material I used for the prototypes (about 0.7mm thick, softer and unknown origin).
The clear material is harder to cut and even if you do puncture it or break the surface, like by pressing a thumbnail into it quite hard, it is stable enough to not start splitting open. So it shouldn't fail or come off completely even if it's in really bad shape. Once it get's damaged it should still be replaced as soon as possible but it won't cause immediate problems with gameplay like the prototype did.
Can't exactly stop a realtime speedrun to swap a cap out...
Finally I'll be adding a thin strip of double sided tape around the edge of the cap to pad the rubber against the metal and to really ensure it won't be splitting open or sliding off should it get damaged.
Silicone rubber isn't the most durable of materials but for this kind of thing I love the stickyness and feel. Hopefully with this new approach and user replaceable sleeves it should work out well.
Here is a stress test to see if I could get the clear sleeve to fail completely once it had been severely damaged all the way around the edge.
1mm Clear Cap Destruction Test
It's pretty solid!
An upgraded clear cap is headed to Biinny for further field testing, Fingers crossed
For the others I suggest keeping anything remotely sharp away from the rubber cap! and if you can, take the rubber sleeve off and apply a narrow strip of double sided tape onto the aluminium edge just to help prevent the same thing from happening.
Don't rely on them for anything critical in stock form!
I'll look at getting some upgraded caps made and sent out to the early testers as well, probably once I get some more colours in.