Front wheel drive recumbents not requiring welding are popular in instructables:
I did one myself : https://www.instructables.com/id/simultaneously-pedalling/
These front wheel drive bicycles are easy to build, cheap and do not require welding. However, they have two main problems: steering is affected by pedalling and traction is lost uphill because the weight is shifted to the rear wheel. You may get used to compensate the steering influence of pedalling but it will always be impossible to use the bicycle on a hilly terrain. My rear wheel drive bicycle overcomes these problems while keeping the simplicity of construction of the front wheel drive ones.
Step 1: Materials
- Two bicycles. From one of them only the crank related parts are used.
- Two clamps (10 €) of the kind used to fix parabolic antennas.
- Two plastic tubes, inner diameter should allow passage of the chain. I bought chain tubes made specially for bicycles (5 €), but you may use any tube, for instance those black tubes used for irrigation.
The upper section of the chain should be straight, the lower doesn't. Keep the end of the tubes close and aligned to the gears.
To guide the chain with tubes is easier an cheaper than using pulleys, springs and gears.
The position of any bicycle seat may be shifted some centimetres horizontally, just by loosening the nut and moving the seat. In order to move it even further; I turn 180 degrees the seat clamp, as in the image.
I mounted a handlebar with a threadless stem because it happens that the tube of my seat is exactly the diameter of a front fork steerer tube. However, all kinds of diameters are used for bicycle seats. You may find many other ideas for seats in the instructables relating to recumbents.