I have so much…
A lot of this I couldn’t do but… a lot of it I probably could. I’ve designed and built quite a few weird machines for people who were paying me, but probably the simplest thing for me to make in preindustrial times would be a battery and an electric motor.
Congratulations, you’ve just earned a stoning by the town mob.
Unless you can make an electric motor that goes with your electric generator, you’ll just be killed as a witch for making a device that hurts people with invisible energy.
Also, good luck not just getting brutally murdered for being a weird person that doesn’t speak the language and is dressed funny. For like half of human history, even describing a magnet would be nearly impossible, let alone finding enough magnets of similar size and strength, and having enough money to purchase those rare items and thinly drawn copper.
If a guy came up to you today, dressed funny and talking in broken Spanglish or something asked you for a small loan so he could buy some deuterium and promethium to make a fusion-tap-quark drive so he can advance humanity, you’d probably run away. A thousand years ago you’d probably just have been stabbed on general principles.