That depends on how long it takes you to write up a patent application, then build and shop a prototype I suppose. You could earn 20 years of royalties at some

That depends on how long it takes you to write up a patent application, then build and shop a prototype I suppose. You could earn 20 years of royalties at somewhere between 5 and 15% with a couple hundred total hours total investment. Of course, the subject matter knowledge required to come up with the invention will be higher, but from my perspective that part is fun.