So… one of my teams called me over today to show off their chain tensioner. Now, they are NOT actually doing this and the sprocket is already mounted on a supported axle so that it forces the chain inward to engage more teeth… but this thing worked… strangely well. You could bump it laterally with a lot of force and it kept working.
Have you guys ever seen a robot use something like this?
I think they look neat, and people can’t believe they work. I’d have no issues using them in vex at low speeds. There’s even a commercial version for industrial equipment (slightly different in that it is flexible): https://www.roll-ring.com/?lang=en
Yes, they will shorten the chain, but that will only remove slack up to the whole link count.
Then by moving floating sprocket along the chain, you could achieve very precise tensioning adjustment of the fractional link length and with the minimum number of parts than any other tensioner design.
And, in case of the failure, you will have to deal with broken chain stuck in your robot, regardless of the tensioner design.
If using a normal motor/engine as power source and lubricated roller chain, then yes. But this is none of those. A chain tensioner also holds the chain taut… something that vex chains do not like. A taut chain (not overly tight, just taut) will cause an extra 1-2 watts of friction in testing.