This shows how the chain stays the same length:
The shifting axle pivots around the gearbox axle and the chain doesn't change tension. The triangular plate highlighted in the back has the bearing and slides up and down on bronze bushings in the smaller slots.
This shows the delrin piece it slides on:
In the physical shifting mechanisms we powdercoated the linkage plates which makes the shoulder bolts bind up, in the next iteration we're accounting for this with undersized spacers.