In this video, Dave installs a Schlumph High Speed Drive on a Catrike. 
With Schlumpf’s gearing systems, two gear ratios are available without the chain moving between gears, and there’s no front derailleur, shifter, or cables to maintain or clutter up your bike. You simply shift with a quick heel movement against the push-button axle in the center of the crank arm. The gearing systems use a clutch plate design that won’t slip under power and they require very little maintenance.
We offer two versions, the High speed drive as well as the Mountain drive and we have all the proper tools to professionally install either on most any recumbent trike and two wheel bikes as well. RETAIL $799
For a more lesser expensive option, check out the Metropolis crank set below. It uses a shifter instead, has a huge gear range, and is around 1/3 the cost of the Schlumpf drive systems. It does not require the boom be machined and can be installed by pretty much anyone….. saving you install and machining fees. >>>>