[Jizvonius]

You can try a floating tensioner depending on the diameter of the sprockets and the center distance (if it's too far, the tensioner will just make the chain touch for 14 tooth sprockets). This should work the same in both directions. as for not using sprockets for the rollers, you could use plastic sliders (preferably something like UHMW polyethylene or acetal)

How exactly to implement it would be dependent heavily on the dimensions of your design. but to get the basic idea here is a picture.



You could have a bottom slider with rails/bolts and a top one with through holes. Then you just need to tighten using nuts above the top slider.