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?
And of course… Opinions?
please no
Whatever you do… don’t do 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, why not?
Especially, if they decorate it with a spinning optical illusion art:
The judges will definitely like it 
Because when it breaks there’s gonna be a big spiky wheel in the middle of the robot.
And they could just shorten the chain rather than have it longer and use a tensioner.
Because when it breaks there’s gonna be a big spiky wheel in the middle of the robot.
I Disagree. There will be a large spikey wheel flying off the robot and rolling across the field towards…
If you do this, you better name your bot Blanka.
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.
like this
Realizing that a loose sprocket can potentially jam inside the bot is correct.
But also realize that it’s a certainty this sprocket causes increased chain friction.
this is something that physics teachers usually refer to as “negligible”
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.
this does not hold the chain taut. look at it.
Actually, the chain was fairly taught. (The animated gif jerks a bit because the camera was handheld.) There was very little slop.
Floating idler sprockers work better when used with metal roller chain that has finished “stretching”, such as the 25-pitch or 35-pitch used in FRC. I’ve successfully used them on several FRC robots.
Is that GUS??? 
Yup, that photo is from GUS’ 2009 robot.