Ahead of our big summer vacation, an early-July thing so you know how far behind I'm still running, we hoped to build something for our pet rabbit. He can barely move his hindlegs, and there's almost no using them to move around. His front legs are good, though, and surprisingly powerful. When he wants to get away he's capable of a speed you'd think impossible for a disabled elderly rabbit. But there was a possible coping mechanism. Why not build a wheelchair?
We had visions of our rabbit racing about the house inside a PVC frame. He's smart, strong where he's able to. Why not?
Well, the first reason is there's no good plans for a PVC-frame rabbit wheelchair out there. There's one set of plans anyone can find, built for someone whose rabbit had a broken leg or something, and which apparently never actually got used as the rabbit recovered. They don't describe how long the various legs should be, or how long they should be relative to the rabbit. We made our best guesses based on our suspicious rabbit and spent some time trying to cut PVC pipe while yelling at each other. We don't really have the vise and sawblades that would made cutting PVC pipe easy.
Much more challenging was sewing the fabric harnesses the wheelchair would need: a sort of double hoop for his shoulders and chest, and then a larger saddle for his back. This required a lot of hand-stitching on 
bunny_hugger's part, including a lot of hand-stitching velcro onto fabric, so the fit could be adjusted. We don't have the sewing machine that would make this stuff easy or tolerable.
Ah, but finally we had everything glued together, a set of wheels --- repurposed lawnmower spare wheels --- affixed, a harness put in, and we could fit our pet rabbit in! And his reaction?
Was to scoot backwards trying to get out of the thing. So far as that would go, which wasn't very far. The frame kept dragging on the ground. It was simultaneously way too small and way too front-heavy for him.
We made some modifications, hoping to keep it from dragging. What we got was our pet rabbit trying to scoot out of it until he gave up and flopped over, waiting to be let out of the thing. No racing around the house, not in this.
We've got ideas for an alternate frame, one that seems likely to be less sensitive to measuring the rabbit. And probably easier to set rolling. But even though we had resolved the first attempt at the wheelchair was probably going to fail and it would be a stroke of great luck if it didn't, giving it up for a loss hurt.
Trivia: From the 7th Century Japan and Korea imitated the Chinese civil service system of examinations. In the Japanese version only nobles were allowed to take the examinations. The Korean system exempted the sons of higher-graded families. Source: Empires of the Word: A Language History of the World, Nicholas Ostler.
Currently Reading: The Art Of Jay Ward Productions, Darrell Van Citters.