Single wheel trailer?

[Si]

I feel a need for a single wheel (bob yak type) trailer*.  But I don't feel the need to pay the prices that these or the cheaper copies have attached to them.

So I'm thinking about a home build.

The trailer itself is no problem - it's just an old fork, mounted horizontally with a small wheel and some cross struts to brace a deck.

The problem comes with the hitch and the pivot(s).

A ball join pivot could see the trailer falling over sideways when not loaded.  But would a single plain pivot work when cornering?  Could I built the trailer as two horizontally positioned forks, such that the tops of their steerers were joined with a hinge, with one fork going back to the trailer wheel and the other going forwards to the bikes back wheel dropouts (obviously might need the legs opening out a bit or an extension mount built).

An alternative would be to have the mount on the back of the rack.  I'm thinking that this ought to get away with a uni pivot and weight at the front of the trailer bed ought to stop the trailer from flipping sideways?

Or should I just buy a dirt cheap second hand tag-a-long and build Xtraycle like mounts on to the sides?

All thoughts appreciated. 


*I have a two wheeler but it's a pain to get down the alley by side of my house, given its width (anyone want to swap a two wheel cargo/dog trailer for a single wheeler?).

[Si]

Actually, thinking about it, I have confused universal and ball joints haven't I?  So a universal joint should work as long as it doesn't let the trailer rotate about its long axis.

But thoughts still appreciated (for instance where to get a strong but cheap universal coupling)!

[Hello, I am Bruce]

I've got a Yak clone. 

The trailer can yaw where the hitch arms meet at the front end of the trailer.  This is achieved by having them stuck onto an axle with plastic bushings.  Perhaps you could build a more substantial version of this using a headtube-headset-and-steerer.  This allows the trailer to follow when steering, but without allowing the trailer to roll (fall) over.

The trailer can pitch where it clips onto the bike's rear axle.  This is achieved by the hitch being slightly loose (there's no bearings).  You could buy a real trailer skewer to do this (the front of the trailer arms just need to be dropouts with some sort of clip).  This allows the bike to bump up and down over uneven roads.

Both arms yaw independently, to allow for any width of rear dropout.  If you are building for your own bike, this may not be necessary.

Unlike a 2 wheel trailer, you don't want any more degrees of freedom, or it will roll over.

[Wobbly John]

I made one using the 'forks' and head tube from one of those micro scooters. To mount it I used a bit of seat tube and top-tube cut from an old bike - this attached (upside-down) to my seat post and stuck out horizontally from the back of my bike. A quill stem fitted into the top tube and gave me a release mechanism (using th expander bolt). I got a short length of 1" Aluminium rod and drilled through to take the scooter's front wheel axle. This went in the handlebar clamp of the stem and in place of the front wheel of the scooter. The head tube assembly of the scooter was disconnected at the folding part and I managed to find square steel tube that was a good fit, to enable me to extend the scooter's "down-tube" to reach the trailer bed. I used the remainder of the scooter as the chassis of the trailer, and drilled through the steerer of some normal length forks to bolt them in along the slotted base of the scooter platform to extend the chassis and mount the wheel. I jut used plywood for the trailer platform.

I still have the remains of it (I didn't like it as much as my other 5 trailers)  

Heres some photos I just took to try to show the ideas:







(i've just realised that this is the one where I did away with the trailer chassis and bolted the scooter bits, and some angle iron wheel mounts, straight to the sheet of plywood.)