This is my attempt at a single wheel trailer. Those of you that have attempted a d.i.y single wheeler will appreciate the difficulty and complexity compared to a two wheeler.
I have used dumpster rescued materials as much as possible, but for this project I had to buy the tie rod ends. the Action Packer tub is one that I've had for years and have used on a previous 2-wheel trailer project. I enlarged the cargo area of that trailer and sold it, but kept the tub for this project.
Chassis design is in 1" square tube. Rear wheel sits in a road bike fork.
That's a 26" hybrid fork and 1" threaded headtube with the original head bearings acting as the main lateral pivot axis between the trailer and the bike. The steerer tube on the fork was cut off and welded back on at 90 degrees.
The dropouts were cut off the end of each fork leg. A high tensile bolt was welded on each leg, to mount a tie rod end. The length of each leg can be adjusted then locked in with a nut. This allows fine adjustment to allow for assembly inaccuracies and line up the trailer with the bike.
The bits that go on the bike. These parts need to be designed for your specific frame. I used the fender mounting point to secure the plates against lateral torque forces - something that you don't have to deal with in a 2-wheel design. The friction between the plates and the frame is nowhere near enough to resist the lateral torque.
A bad pic of the trailer hitch..
The final product with a very happy little boy that got a (very slow) ride in the trailer.
Performance-wise, I've used it multiple times for groceries.
With no load it tracks perfectly true behind the bike but can get a bit skittish in fast cornering on rough ground. however, you'd already be cornering dangerously fast even if you weren't towing a trailer, and most two wheel trailers would have already rolled over at those speeds.
Anything up to 35 - 40 pounds and it tows rock solid with no handling vices or influence on the bike provided the load is as far forward in the box as practical. The further forward, and low, you can place the load the better it tows. At the sort of speeds a sane person would do, it's unaffected by mid-corner potholes.
As the weight of the load increases over 40lb the handling starts deteriorating. The most I've had on board was 65 pounds which was just dangerous at anything over fast walking pace. The further forward you keep the load the better it handles.
The lower resistance (part aero part rolling resistance) advantage over a typical two wheel trailer is readily apparent if, like me, you like to move fast when towing a light load. The hitch system is absolutely solid with no slop and no binding around the pivot points. I'm very happy with the results, it turned out even better than I expected.
If anyone would like details beyond these pictures just ask, I'm always happy to share. Feel free to duplicate any/all aspects of the design.... Now I just have to get around to cleaning it up and putting a coat of paint on it.