Originally Posted by halfbiked
In the most sincere form of flattery, I will copy the ideas that
these guys use (for a motorcycle trailer). Basically you use a universal joint between the bike & the trailer. This allows relative motion in two planes: left/right (turns) and up/down. But not lean - the trailer will always lean with the bike.
But for bicycles, a hitching system similar to the Bob trailer can be easily duplicated and might be more practical than U-joints.