[sanddrag]

At Long Beach we had trouble with a slack chain on our lifter arm. We used a floating idler for a couple matches and it solved our problem. We switched to a a rigid idler sprocket on bearings which worked perfect.

I've tried spring loaded tensioners before. They only work well in one direction. I wouldn't recommend it. Rigid is best. Best way is probably to make one end of your mechanism sliding, to increase the center distance.