[ErikJ]

Something our teams have done in the past is use an adjustable piece of delrin or HDPE as a tensioner. The simpliest of these was just a piece of round stock with a hole drilled through, off center. The chain runs over this piece, and by rotating it you can adjust the tension (since the hole is off center you've got this cam sort of motion going on). Sure you've just added some losses into the system, but it doesn't get much simpler than a piece of round stock cut to length, 3 holes (2 chassis pieces and a delrin) and a fastner. We've used a few variations on this over the years, but that was the one I liked the best. You have to keep an eye on it in case the tension from the chain causes the piece to rotate the opposite way and loosen the chain, but that's a simple fix.