Differential Dynamics Corporation (DDMotion) has developed river turbines based on three building blocks: proprietary mechanical three variable gear assemblies called Transgears, the principle of rotary frequency converters, and proprietary Variable Overlap Generators. Speed converters designed with transgears convert variable speed to constant, and can handle higher power compared to transistor-controlled power converters. The technology is applicable for harnessing renewable energy (e.g. river, tidal, wave, and ocean current), automotive transmissions, HVAC compressors, and other motion control applications. The first product developed is river turbines controlled by a speed converter "Hummingbird". The turbines can be either grid connected or stand-alone, distributed generation.