[elil]

I highly recommend an idler pulley. My team has used a bolt with a piece of pvc around it. To attach the bolt, we tighten it with a lock nut through a slot on a piece of sheet metal. The one thing about this is that the nut has to be really tightened down. Otherwise it's about as light and simple as you can get.

We've also used spring loaded tensioners. These had their advantages and disadvantages. The big advantage was never needing to worry that the chain was tensioned after the tensioner was attached. The disadvantages are of course cost, but also weight. Additionally, support like a wood block must be added to the bolts used to attach the spring tensioners if they cannot be mounted directly onto a frame element.

We have also used 3d printed pieces on a belt drive. They are a half moon shape sized to tension the belt without needing to be adjusted.