Step 1: Layout of Parts
In addition to the rusty bikes, I had a cheap kiddie bike from Goodwill ($4) and an old golf bag cart that was also bought cheap at Goodwill. It was very sturdy and had lots of metal parts that could be used on various projects. I used the frame of the kiddie bike, a fork from another bike, handlebars from yet another bike, and the wheels and handle of the cart (the handle was used for the seat post). The front rim was actually a stray that was bought at a sell-off from a nearby Kmart store that was closing down (boy did they have lots of goodies they were selling off that I wished I could have bought! Including a bin full of brand new shopping cart wheels!). I already had a tube and tire that were the right size for that rim.
Once I had the crazy trike idea in my head, I laid out some of the parts to see what work I would need to do next. First I removed the fork and handlebars from the kiddie bike and replaced them with a bigger fork and different handlebars. If you are new to working on bikes and either find yourself with a pile of bikes of your own or wanting to accumulate a pile of bikes, just keep in mind that not all parts will be interchangeable, and if you don't have the tools and know-how to make everything fit the way you want it to, you may need to be careful of the sizes and styles of bikes you get. This may limit the kinds of projects you will be able to complete.