Honk If Parts Fall Off: A Not-So Successful Upgrade

I explained in a previous post that I had put effort into making a new version of my cybernetic arm for my return to Neotropolis in 2025. In that earlier post, I described some of the shortcomings of the previous version that I hoped to improve on, and some of the solutions I was trying to address them.

Now that Neotropolis 2025 has come and gone, I can report that the new arm was not quite the upgrade I had hoped it would be. But it did offer some worthwhile lessons learned.

Before I get into the full analysis of what went right and what went wrong, I would like to show off a few photos of how the finished piece looked before going to the desert. It did look nice, even if it didn't quite perform up to expectations.

What Went Right

One of the key improvements I planned for this version was the addition of a zipper as a closure so that the fore arm section could be form-fitting to my actual arm while allowing my hand to pass through easily. As a proof of concept, that worked extremely well. Sewing the zipper to strips of pleather, and then contact-cementing the pleather to the EVA foam held very well, and the zipper provided an ideal closure for a form-fitting forearm piece. I did make the fore-arm a little too snug overall, so it felt uncomfortably tight when the zipper was closed. That is an error to be corrected in future builds.

What Went Poorly

Adhesives - Adhesives are a tricky thing. In a lot of cases, you can reliably predict how they will behave, but given the abundance of different materials we work with as makers, there will always be an element of experimentation. Contact cement is a tried-and-true option for connecting EVA foam pieces to one another. But when it comes to connecting EVA foam to other material, it can be less reliable. That proved the case with the glove portion of my arm. In this case, the EVA foam pieces were cemented to Ya Ya Han stretch pleather fabric. The bonds between these materials immediately began to break down when the piece was worn at Neotropolis. I suspect the dry air and extreme temperature changes played a part in this. Fortunately I had a bottle of CA glue in my repair kit, so I could provide quick fixes. But one of the finger tips did fall off and was loss while I was away from camp.

Magnets - I used magnets to hold a panel over the inner surface of the forearm, covering and hiding the zipper. Using rare-earth magnets is a pretty frequently used method for adding temporary connections between cosplay elements, and typically works well. I think where mine went wrong is that I was attaching a rigid piece made of Worbla and 3D printed pieces, to the soft, flexible surface of the EVA foam. So while the foam could flex to conform to the movement of my muscle and bone, the Worbla plate could not and so the magnets were easily separated. The result was that the panel was frequently coming loose and falling off. I tried some improvised solutions by added two large snap buttons and couple of stronger magnets, but these were largely unsuccessful. A better solution might have been to make the panel from 2mm EVA foam and flexible TPU printed pieces to allow some give. And to use a smaller number of much stronger magnets.

Sleeve Fabric - Beneath the foam segments, I wore a black fabric sleeve. This serves both to fill in any gaps between the pieces so no bare skin would show, and also to provide a breathable lining between my skin and the foam. For the first version, I used a black four-way stretch fabric that worked well. For this version, I used a black stretch mesh fabric that was much thinner. It was so thin that it felt fragile and could be difficult to remove from under the upper-arm segment without feeling like it was at risk of tearing.

Bulk - One of my stated goals for the new version of the arm was to make it more streamlined and less bulky. The hope was to be able to easily wear it under my jackets, without having to remove sections like I did with the original version. Unfortunately, after some sub-optimal results with attempts to build the arm out of Worbla and 2mm EVA I ended up reverting back to the reliable 5mm EVA. While I did reduce the overall bulkiness of the arm by removing features like the retractable "data jack" and an unused battery compartment, it still ended up adding too much thickness to my arm to fit through the jacket sleeves.

Lessons Learned and Future Plans

At present, it is doubtful that I will be returning to Neotropolis in 2026. Still, I've enjoyed wearing my cyberpunk gear at cons, and it would be pretty cool to continue to refine the arm as a costume piece.

If I continue to use foam or Worbla, the zipper closure will definitely still be used. I will just need to do a better job with the fit of the forearm to avoid it being too tight again. I do still think magnets are the way to go for adding a piece to cover the zipper. It's just a matter of using a smaller number of well-placed, stronger magnets.

Cosplayer Lorentz iWood shared an idea for designing finger armor as "gloves for your gloves". Meaning that the armor pieces are never permanently attached to the base glove, but instead the hand armor (whatever material is used) is a single connected unit that slips over the glove and is fixed in place using a wrist strap.

My blue-sky hope for a future version of my cybernetic arm would be get sufficiently good at Fusion 360 or Blender to 3D model and print the pieces. 3D scanning apps for mobile are becoming pretty good, and I could probably get a scan of my fore-arm to use as a base for a form-fitting design. I don't know if that is going to happen in the short term though. Hopefully I can set aside time for regular practice with these modeling tools.