The hitch pin needs to be a SOLID vertical pin.
The connection is a vertical tube over that pin, with a horizontal joint either
ahead of, or
behind it.
You CAN use a simple U-joint, but the problem will be realized when you lean the bike over in a tight turn. the U-joint has the axis of both joints on the same plane. This means that when ONE axis leans (the bike is leaning to the side) and the trailer is turned to one side or the other, the other axis is also forced to lean (forcing the trailer to want to lay over on it's side unless it is precisely in line with the bike). With the axis of the horizontal joint
ahead of or behind the vertical joint, when the bike leans over, the horizontal joint will
rotate around the vertical pin and the trailer will remain vertical.
Check out this hitch and trailer that I built for my friend Sean. This is
"The Colgan Hitch." His idea and design,
my welding and fabrication!
http://www.myspace.com/elraisuli/photos/11235727#%7B%22ImageId%22%3A11235731%7D
For this particular scooter, I modified the original intent of the hitch a bit so that the bike would tow either the single-wheel trailer
or the traditional ball hitch trailer. The hitch pivots on grade-8 bolts at the ball hitch plate and the shock mount bolts, as well as at the two top bolts. When the rear suspension is compressed, the ball remains in line with the bike, but moves backward slightly and the ball mount plate rotates slightly backward with the geometry.
In order for the trailer to remain vertical when it is turned and the bike leans over (on the side stand, for instance)
the two joints CANNOT be on the same plane.
In this photo, you can see that I simply welded two tubes together, at 90 degrees, so the axis of each tube was on a different plane. This SOLVED the tip over issue. It is up to you whether you want to place a tube spacer between the two tubes so that the vertical joint and the horizontal joint are farther apart, but it isn't necessary.
Once the proper bolt was selected, it was welded into place. A crown nut with a cotter pin or R-Hook goes through a hole drilled at the correct point so the nut will not back off when the trailer turns from side to side.
This is the
shortened tongue! This tongue used to be 12 feet long, and had a brace at the front. the scooter towed a 17 foot canoe on top!
