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.
Step 2: Attaching Cart Wheels
First I test fitted the bolt before cutting a piece of scrap pipe to wedge where the wheel hub would normally go, just like in the Instructable I mentioned. Next, I put the section of pipe I had cut into the neck I had picked out, centered it, and made sure it was tightened as much as possible. The post of the neck needed two holes drilled straight through it in order to fit bolts to attach it to the golf bag cart wheels. That was probably the hardest part of the project- i don't have the proper tools to do that sort of thing the right way, but I took a chance and "eyeballed" it, quadruple checked as I went along, and managed to get it close enough to get the bolts to fit and for it to work. At this point, the back wheel section was ready for the bolt to be put through the pipe and for it to be attached to the frame.
Step 3: Checking Alignment and Final Assembly
Once I had it on all three wheels, I realized that the back wheels were likely to cave in where they attached to the frame. Since this is a weld-free project, making a sturdy structure becomes a much bigger challenge. I added a threaded rod attached to the bottom of the wheel post on one end and to the frame near where the kickstand would have been to keep the back wheels "pulled in" so it would not cave down when someone sat down on the seat. So far, this has worked well, but has not had more than about 75 pounds of weight on it. I don't think I would use that setup for any more weight than that or for going high speeds or on bumpy roads. If your rider has the leg-reach, you can use bike pegs on the front wheel as foot rests, or rig something to go through the hole where the pedals used to be. You don't want it to stick out too far or get in the way of "walking" the bike to get it coasting.
So for a first attempt at a bike build, I think this was fairly successful and I learned a lot. I plan to use the cart wheels on a future project, so I will probably separate the front and back of this bike and use them on two separate projects. I still want to make a drift trike, and I think the cart wheels would look awesome on the front end of some kind of bike. When I get another build done, I will post it here on Instructables.
Please offer any tips and suggestions you may have on how to solve some of the issues I mentioned, especially the structural issues. Thanks!