I'm a newbie and very happy to have stumbled across this trove of information. I just bought my son a Kettler Trikett tricycle (he's 2). It's a nice unit, and I'm happy with the purchase -- and more to the point, he's happy. The reason I bought it is because rather than have the crank drive the front wheels directly like most trikes do, this vehicle has the pedals driving a sprocket and chain that goes to a sprocket on the rear axle, much like a conventional bike.
But I'm disappointed in one aspect of the trike. I was hoping that it would function like a bike with a coaster brake -- he could pedal, coast, or brake at his option. But it doesn't -- the gear is fixed on the rear axle. Well, this isn't exactly true -- there's a lever that engages or disengages that sprocket, but you'd have to do this every time you want to coast. Not cool.
So I'm hoping to pick the brain of someone with more brain to pick than I. Would it be possible to modify this bike to approach the functionality of a traditional bike with a coaster brake? I'm certain I can find a rear hub from a child's bike. The rear axle is just a long steel rod. I think my problem will be that in this bike, the sprocket drives the axle and the axle drives the wheel -- whereas in a regular bike, the sprocket drives the hub and the hub drives the wheel, and the axle is always free. Can someone help me brainstorm this problem?