Recently, i have found a bunch of people asking about how to build something in hardware, (for example: 1, 2, 3), and don't seem to be able to find an appropriate tag for it. I think we need a new tag like: "construction", "building", "mechanics", or "linkage". Additionally, we definitely need "hydraulics", and "pneumatics". The only hardware tags that we currently have that come close are: "Mechanism", "Chassis", "Platform", and "Frame". Of these, mechanism is probably the best, but i think there can still be lots of "how to build this" type questions that "mechanism" isn't a great fit for.
Tags tend to be generated as an when they are needed, but without tags existing in the first place it can be difficult to get them to arrive spontaneously, so suggestions are always welcome.
As such, if you see a question which could benefit from better tags, feel free to add them. If you also fancy adding a tag wiki entry for the tag, even better.
If you are planning a wholesale re-tagging exercise, it would probably be a good idea to seek consensus from the community through meta first, but Robotics is created by the community for the community, and anything which makes the community stronger is a good thing in my eyes.