Electronic gear shifting
Electronic works without bowdens. The system is digital. There is no wound steel cable. Instead, there are multiple combinations of 0 and 1. A battery placed under the frame powers the system. Each battery should last for 1000 km depending on the manufacturer. Then it needs to be recharged.  Wires for data and power are hidden inside the frame. Parts of the shifting systems are connected to each other. Servomotors do the shifting. The shifter and derailleur have a pair of servomotors built into them.  There is a self-adjustable microchip in the derailleur. The system has its own logic, which keeps the chain from dropping. There is no need for maintenance because the derailleur adjusts itself using the microchip.