[Madison]

I've attached a *quick* sketch of what I have in mind. Bicycles have a one way bearing. . .our robot would not.


I've kept the sprocket that traditionally acts as a tensioning sprocket, but I've fixed its position relative to the actual sprocket that causes the gear shift. Thus, there's no tension taken up at that point, and the torsion springs aren't necessary. So, going backward, this ought to keep tension in the right places and make the sprockets turn.

To take up slack, I moved the tensioning mechanism to some other place outside of the derailleur mechanism. Where it goes, really, is irrelevant, so long as it goes somewhere.

Does this make sense?

It still couldn't shift in reverse, but it should be able to drive backward.