A patent was issued on January 1, 2019 for VECTr – Variably Expanding Chain Transmission. VECTr is an expanding chain ring system which allows one to vary a bicycle’s gears from 29 to 44 tooth equivalent settings.
By using a lever shifter or an index shifter calibrated to VECTr’s settings, one can change gears as quickly and as easily as on a derailleur system. Watch the video from VECTr – Variably Expanding Chain Transmission:
Since the gears changes are not made while the chain is under load, nor between parallel chain rings (as on current derailleur systems) there is no chance of the chain slipping of falling off.
A prototype is planned, but I am also seeking to license VECTr to a qualified manufacturer.