Some footbikers might be interested in this; I got into footbiking as a bicyclist with a simplicity fetish, and have continued using a single-speed bicycle for some tasks.
Retro-direct gearing uses no levers or cables, just two independent freewheels and a chain-tensioner. The chain is routed from the chainwheel to one freewheel, looped around the chain tensioner and back to the other freewheel in such a way that one gear is accessed by pedaling forwards, and one by pedaling backwards.
As to the mechanics, two single-speed freewheels were joined using an old bicycle bottom-bracket cup (which has the same threading as the freewheels), and a KORE chain tensioner was deployed near the crankset. That’s it, except that I joined two chains together to reach the necessary length.
Like some other modern adherents, and contrary to the traditional setup, I use the forward-pedalling gear for my lower speed (for starting out, tooling around and hill-climbing) and the reverse-pedalling gear for higher-speed cruising. Pedalling backwards is bringing new muscles into play; I feel it in the back of my thighs, but choosing between two gears is pretty intuitive otherwise. (I’ll see if the development of these muscles brings anything to the footbike.)
I live where the Wright Brothers came to fly their aeroplanes; one reason they chose the Outer Banks was that these barrier islands are quite windy. The main roads run roughly north and south, and one often pedals or kicks against a 10-25-mph wind or with it. With the footbike, it’s pretty easy to deal with the wind, less so with a single-speed bicycle, if you have limited patience with derailleurs, cables and levers.
Okay, the next ‘blog entry will be about footbikes, I promise.