Rusty’s a good scientist.
It’s not that he’s unable to come up with anything good; rather, society views his inventions as too radical.
Rusty is dealing with Luddites.
We’ve certainly seen him develop new creations. Unfortunately, the “Joy Can” was powered by an orphan heart. This is comparable to modern society’s struggle with stem cell tissue research. It is conceivably his own creation.
At the very least, it was one of his father’s many fantastic unfinished creations. It is likely that any project his father would have abandoned would have been stopped because of moral or ethical considerations. Although, the Ooo ray was technically a “weapon of mass destruction” Rusty had never considered it as such.
Some famous scientists are only able to narrowly focus their attention on their particularly narrow field.
Then there’s the metasonic locator. We never get to see this actually in action, other than it emits large white rings, awakens “Ghost Astronauts” and comically oversized shellfish. But, according to its description, this device is some sort of time travel viewer that can be shown on objects to reveal what they looked like in the past.
Lest us forget, Rusty does, in fact, locate the flying saucer.