I posted this originally in the 'Utility bike' thread, but perhaps I should've put it here.
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I've attached a photo of my lovingly made bicycle trailer that I built over a few weekends. A few bits are recycled; the wire mesh bed and the golf-cart universal joint. It is used primarily for shopping, although when I'm convinced it's sufficiently durable I may take it on a tour.
I also made a short film to demonstrate to my friends that it works.
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http://www.youtube.com/watch?v=UaQJIdpVRYc
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Usually my constructions fall a little short of my expectations, but for some reason this worked out perfectly. If you remove the wheelguards it even runs upside down, which, of course, is very useful. The universal joint has three mututally orthogonal rotation axes which allows the trailer to adopt any orientation. As a result you never really feel the trailer since, apart from its inertia, it doesn't apply any stresses on the bicycle. I've carried over 100lbs on it, but I don't think I'd do that again, 60lbs is probably its ideal carrying capacity.
More recently I've added two dynamos, rectified, smoothed and regulated to produce a total of 18volts and 1amp. This drives some surprisingly bright 10mm LED arrays I put together (even at 5mph), or a small bank of electronics which supplies regulated USB power and firewire for charging ipods etc, diode-protected NiMH cells. It also takes power in from a nice 8.1volt solar panel I found on ebay, which may prove useful on a tour.
Well, I think that covers everything.
Since it has been such a boon to my life, I may eventually make a follow-up video more concisely following the trailer's development. I wish there were more homemade bicycle trailer videos on youtube.