If we feel like complicating things, we may look at a relatively simple yet really effective system : the double-cone clutch.

It's a bit more effective than a belt-tensioning system, but harder to make, but it's a kind of challenge ^^

there's a nice website to calculate the optimum dimensions and stuff for the needed application (well kind of) (link)

We'll see ¯\_(ツ)_/¯

image courtesy of here