This blog post was originally sent as an email update to our mailing list on 01/03/2022.
For the December update, I'd like to shed some light on the choice of cable for the Hydrogen. We spent a lot of time testing many different cables before we decided on one because the cable is critical to the performance of the mouse.
We chose a lightweight polyurethane (TPU) sheath which, when paired with the stranded conductors, gives the cable excellent durability and flexibility. The aramid fiber core (the same material Kevlar vests are made of) provides extra protection for the delicate conductors inside.
Our cable is flexible, lightweight, durable, and very thin at a mere 2.5mm in diameter. It’s as light, agile and high-quality as the Hydrogen itself.
For those who are interested, the rest of the email goes into some of the factors that we considered in order to make our choice. I hope you learn something!
What's important in a cable
The only time a user notices a cable is when it causes problems. Aside from a cable breaking because it wasn't durable enough, or getting in the way because it's not being managed by something like a bungee, the biggest issue is movement resistance.
Movement resistance is the most difficult issue to solve, and it's very important because it's always there. It causes issues physically by resisting the mouse movements, but also mentally by being constantly distracting and annoying.
The stiffer the cable, the more resistance there will be when moving the mouse around, and the less uniform the movement will be. There are generally two major factors that contribute to cable stiffness: the conductors, and the sheath -- or the metal inside, and the wrapper outside.
Conductors: solid vs stranded.
The metal in the wire carrying the power through the cable is called a conductor. A very important aspect of a conductor is the gauge. The thicker the conductor, the better the electrical conductivity. On the other hand, a thicker conductor means a stiffer wire, which is easier to fatigue and break.
Since the Hydrogen uses high speed signals, our cable has fairly strict electrical requirements for proper functioning, one of which is a certain minimum conductor thickness. The problem is that if we use solid conductors that are thick enough, the cable becomes too stiff. Luckily there is a great solution to this problem: stranded conductors.
Instead of using one solid conductor, the Hydrogen uses multiple thinner conductors grouped together. Stranded conductors give us the same good electrical conductivity as a solid conductor, while being significantly more flexible and durable.
Sheaths: "paracord" vs "rubber?"
The sheath is the outer material wrapping the wires inside the cable. Its purpose is to protect the conductors. The reason I put "paracord" and "rubber" in quotes is because they're both misnomers.
Parachute cord, or more succinctly, paracord, is a type of rope which uses a core of nylon cords (that's the "cord" part of "paracord") wrapped in a woven nylon sheath. So by "paracord," we really mean that the wires are in a woven nylon sheath.
I say that "rubber" is a misnomer because in the strict technical sense, rubber means natural rubber like latex. Colloquially, when we refer to a sheath as "rubber," we really mean a material which is elastic, or rubbery, i.e. a gummy, squishy, stretchy type of plastic.
In common use, "paracord" refers to the woven style, and "rubber" or "plastic" refer to the solid style. For clarity, it would be best to refer to the style and material of the sheath separately. So most "paracord" would be "woven nylon" and the hydrogen cable, for example, would be "solid TPU."
Why does the Hydrogen have a solid cable?
The woven sheath is flexible for the same reason that the stranded conductors are flexible. Since the woven style consists of many thin strands, a stiffer sheath material can be used without sacrificing flexibility.
While that may sound like a good thing, it is, perhaps surprisingly, the main reason why we decided against a woven cable. While the woven style does provide some abrasion resistance, it completely fails to support the delicate conductors inside. All of the cable bending resistance comes from the conductors themselves. As you can imagine, that is a problem because it means that every movement of the mouse fatigues the conductors inside, which will lead to an early cable failure.
Since the woven sheaths can use stiffer material, they generally have less friction. However, since the texture is woven rather than smooth, scratchiness can be felt on certain types of mats. I consider these to be non-issues because all types of surface drag are minimized by using a cable management solution like a bungee.
I think woven sheaths have a lot of potential, and they're something that I'd like to explore further in the future. As it stands now, the best option for the Hydrogen is the solid TPU cable we chose.
Why does the Hydrogen use TPU plastic?
We tested many different materials for the sheath. Initially, we thought that PTFE (often called "Teflon") would be a good choice of sheath material because it's the same super low-friction material that's used in mouse feet. Unfortunately every cable we tested with PTFE ended up being unacceptably stiff.
PVC is the most common material used for cables, mostly because it's cheap. The PVC cables we tested were generally acceptable, but they didn't stand out. They were decently flexible, and reasonably durable, but nothing special.
The TPU cables on the other hand, aside from being a bit more expensive, are superior in every way. TPU is more flexible, it weighs less than either of the others, and it's much more durable.
Our TPU sheath is just slightly less flexible than the conductors that it's protecting, so as you move around the cable, the plastic takes all the stress and leaves the conductors protected from fatigue. This leaves us with a very flexible cable without sacrificing durability.
Thanks for reading our update. I hope you found this more technical email interesting. Stay tuned for the January update which will probably have plastics details, since we ordered the molds last month and should be receiving the first units in a few weeks.
Happy New Year --