Drive Train:
The chain line is going to be a little tricky, there are several things that make it difficult to route the chain to the back wheel. I am beginning to understand why so many people are interested in exploring front wheel drive designs.
And idler is definitely needed. I'm using and old skate wheel that I notched on my drill press. I used a 5/16" bolt and some fender washers for the mandrel and the cutter is a piece of tool steel the I ground like a lathe bit.
The chain still drags on the bottom of the seat sometimes so I installed a chain tube of irrigation pipe. I do plan to fix this interference but not until I finalize the rear suspension. The few quick rides I've taken so far have convinced me that the mountain bike shock isn't going to work, it's too big and has too much travel.
I am going to make a new rear shock with some sort of elastomer. These are car and truck suspension limiters. I drove my wife crazy the other day by making her stop the mini-van every time I saw one lying by the side of the road!