Simple hitch design that could be used to attach a trailer to a bike. Good for trailer applications where rotation is not needed or not desired, such as when teaching your child how to ride a bike.
Step 1: Not Ideal
It's easy enough to attach hinges to a large L-bracket, but you end up with twisting forces which may not be ideal for your application. With a few saw cuts you can create a better assembly.
Step 2: Materials
(2-4) Short L-brackets
Screws, Nuts (and Lock Washers)
Step 3: Saw a Slot in Each Hinge
My hinge was slightly thick than my saw blade, so I added a 2nd blade to create a wider cut.
Step 4: Slide Hinges Together
For those without welding skills and equipment (including myself), continue to the next step.
Step 5: Attach L-brackets
Attach L-brackets. Depending on the range of motion needed, you can trim the corners to create more clearance.
Note: I tried replacing the L-brackets with a hinge to create a 3rd axis, but the assembly was too unstable. It would be interesting to see how a welded version with 3 hinges would perform.
If you need rotation, there are also several Instructables on how to add a quick release hose fitting.
Safety Note: Since the hinge pins do not intersect, the assembly should NOT be used for rotational applications - it is NOT a universal joint.