Cyclaholic

Ye's, you need a torsionally rigid connection between the trailer and the bike, otherwise the trailer will just fall over.

I'm working on a single wheel trailer now. It's my first single wheel design so I'm using this prototype to test a few ideas, and just to gain some experience on the dynamics. I started by looking at the best elements of the "BOB Yak", the "Third Wheel", and a number of other commercial designs. I then added several of my own ideas and designed it around materials and manufacturing techniques I have at hand.

My concept is a tubular steel chassis that has enough flex at the design weight to act as suspension. That's to alleviate the shock stress on the bike at the hitching point, since it carries about half the weight of the trailer & cargo. The same chassis can use a 700c or 26" wheel. The cargo area is a modular design that will allow it to be easily changed between a hard plastic box with lid, a hammock style net with a couple of duffel bags, or any other specialised module for a specific task such as an animal cage or padded box for sensitive/fragile equipment. There's also a couple of other design elements that you'll just have to wait to see

The hitch is basically the chainstays from two dumpster frames, you can see the donor frames in the first picture. The connecting points are tie rod ends. You can see how they connect to the trailer chassis in the pictures, the connection to the bike frame isn't built yet.

The trailer with a hammock cargo net and the road wheel you see in the photos should come in at around 10 pounds, with a 20 gallon hard plastic cargo box it may reach 14 pounds. It will have a cargo capacity of 70 pounds and could potentially be built lighter without compromising strength..... and it cost almost nothing to build!