The best method of chain tensioning is to properly design your chain run so that there is no need for a tensioner. However, to be more realistic for FIRST, the most robust system of chain tensioning is to be able to vary the distance between two sprockets. Anything else adds unnecessary complexity and strain on what should be a rather simple system.

Once 114 implemented a proper chain tensioning system (Aim High, 06), we did not break a single chain, or have any chain related problems. We have since had zero problems with chain.