Sometimes, all you need to invent something is a good imagination and a pile of junk.

Constraint is a better creative condition than abundance, because limited material forces you to look hard at what you have instead of shopping for what you think you need. Waiting for proper equipment is one of the most respectable ways of never starting. Most first versions of anything were built out of the wrong parts by somebody who could not wait.

Build the crude version this week from whatever is already in the house. It will be bad in ways you could not have predicted, which is exactly the information you were missing. Buy the good tools once you know what you are making.