When I first read this, I though "gee, that's a great idea." But then I remembered something that I've learned from frequenting WhyNot for a long time. If an idea sounds really good, somebody has probably already done it. So I googled and immediately found Magic Wheels 2 Gear Wheelchair Drive. Anyway, good idea.

wow, those are costly. maybe bicycle sprockets with a derailleur would be better. Off the shelf, so very inexpensive and you could design a crank that the person wouldn't have to remove their hands from for every stroke. I've always thought that would be a detriment to pushing a wheelchair uphill. Let go, roll back. Like Sisyphus.But what are the odds that that's been done too...

No one is paying enough for healthcare yet ?