A chain drive is a connection from the leg action to the wheel turning, the connection here between leg action (and generator) and wheel (and drive motor) is a connection of electricity+signal-data (with a potential battery|capacitor in the mix as well).
The drive motor can contribute data on how hard the wheel(s) is(are) to turn, the generator can contribute data on how hard either leg is downstroking, and there can be controller logic making decisions on how to dynamically route energy to and from the battery, increase|decrease drive motor power, increase|decrease generator drag (on asymetric legs (injury|training).
The "drive chain" here is a hybrid of energy+signal transfer .. but digital drive still seems wrong as that's just the signal portion.
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