I need to see photos of bicycle traier U-joints like this one
https://www.youtube.com/watch?v=UaQJIdpVRYc

I want to use head sets or some other method that will make a strong u-joint.

https://www.youtube.com/watch?v=rcAnX...eature=related
At 10.43

A bit weak i would guess.

Here's one I've been making for years. It's held up well and can even twist in the middle unlike regular u-joints. You can see more at www.redbiketrailer.com

Bike Friday uses a standard pneumatic fitting used with compressed air power tools. Here's the hitch:
https://bikefriday.com/thestore/prod...ducts_id=15125 and the trailer attachment:
https://bikefriday.com/thestore/prod...oducts_id=7523

I've had no problems with this fitting on the trailer for my Pocket Rocket and it attaches/detaches in a second by pulling on the spring-loaded collar.

Here's my latest one in prototype.

Its been done.. a hand made exhibition bike trailer,

a Jack Taylor inspired job perhaps?
since they also used bike headsets as bearings.
1 pair for yaw.. another bearing for pitch .. on 2 wheel trailers

1 wheel like BoB trailers just use bushings for their pair of bearings.

I used an air fitting attached to a wheel castor. I have a bob trailer and another trailer that attaches to the rear axle. The problem with the bob is that it does not handle well if you put too much weight on it. This hitch seems a lot more stable than the one attached to the rear axle.