For the last 6 months I've thinking about how to build a tandem recumbent trike using what I've learned from the last couple of projects. I started with some 1.75 inch square aluminum tubing salvaged from the renovation of a doctor's office. The tubing was the frame of an interior glass wall above the reception counter. The tubing was just sitting there waiting to get taken to the dump so I asked if I could save them the trip.
Here's a picture of the cut tube laid out on the floor of the back porch. Off to the right in the dark you can barely make out the back end of a 20" suspension mountain bike. The white circle shows the placement of the front wheels. The beast is long, almost 13 feet. I've designed it so that it will come apart in the middle so that it will fit on the car roof for transport. There's lots to do, but it's always nice to see how its going go together. Like the past projects, the the tubing will be riveted and epoxied together. The seats were purchased from Andrew Carter whose Recycled Recumbent website is quite interesting.