One of my many hobbies is recreational gold prospecting. I've been gold panning on my vacations for many years. It's a lot of fun. It's great exercise. I get to do it in really scenic locations. I have even found some gold. Gold likes to collect in cracks and crevasses and really hard to get at nooks and crannies. What is really needed to clean out those pesky cracks and crevasses is a vacuum cleaner. Problem is, where do you plug it in out in the wilderness? Solution, replace the electric motor with a gasoline engine. Now you have a vacuum cleaner that will work anywhere.
As with most of my other equipment, (recirculating sluice, wind turbine, solar panel, telescopes, jet engine, etc., etc.), I decided to try building one myself, rather than just buying one. The tinkering is half the fun after all. Also, you will get a much greater sense of satisfaction and accomplishment when you know it is YOUR home-built equipment that is doing such a good job, and not some store-bought thing. You can find more information on my various projects at http://www.mdpub.com