Beneficial work involving creating new things?

Designing something to help people with mobility issues is the first thing to come to my mind.

Prosthesis design and building, adding to @lucillelucillelucille ‘s comments.

How about volunteering on a local school or church that needs assistance with maintenance.

Habitat for Humanity always is looking for able bodies to help build and repair things.

Our local woodworking clubs make lots of clever toys to give to sick and needy kids.

You’re describing my job exactly. I work in a clinic that designs and fabricates custom equipment for people with disabilities. I have a shop fully equipped to do all kinds of operations on all kinds of materials, because we come up against so many unusual problems and circumstances and need to be able to respond creatively.

I rarely do exactly the same thing twice. One day I may be machining and welding some metal attachment for a wheelchair, the next day I may be turning a custom knob to fit someone’s hand exactly, or modifying a crib for a mom in a wheelchair.

I work in a team with physical therapists and rehab engineers during the evaluation of the client’s needs, but most of the design work and all of the fabrication is my baby.

Not only do I have the satisfaction of doing shop work (I’m sure you can relate), but nothing beats the thrill of delivering that finished piece and seeing someone’s life get suddenly easier.

Prosthetics/orthotics work is no doubt just as rewarding, but it does require a whole lot of specialized education. I got this job just by virtue of having good and varied fabrication skills. There aren’t a whole lot of places that do what we do here, but check out job postings categorized as “assistive technology” and you might turn up something similar.

Whatever that.company was that build that elevator to lift out those Chilian miners.

Organizations like The Peace Corps would almost literally kill to get someone like you on board!

I like the suggestions other people have posted, and I also think you could be a freelance inventor. There’s no reason you need to work for someone else in order to follow this dream. You might want to find someone to market your ideas, though. I guess one of your concerns is that setting up your own shop can be expensive… but maybe you could borrow a few items as needed, rent them, or buy tools and equipment used to begin with.