just curious: fixies

DD said:

Has anyone ever rigged up a modern recumbent trike as a fixed-wheel drive?

Not very practical. For starters, you can't have any idlers on the
drivetrain on a fixed-gear. You would have to redesign the entire
trike just for that purpose. Also, on a trike, you need the extra gears
to climb. My fixie is setup with a high gear ratio in order to keep up
with traffic, and even thou it weights only 17Lbs it is a pain on any
decent climb. A fixie trike would need to have a very low gear, unless
it was ridden only on flat terrain.

DD said:

Has anyone ever rigged up a modern recumbent trike as a fixed-wheel drive?

Not trike, but there's a Bikee running around town set up as a fixie.
As Joao said, a trike drivetrain would have to be designed around
fixed-gear use. I'd also be afraid (very afraid) of a high-speed
descent tossing a foot and sucking it under the crossbar. Yeouch.

Jeff