Chain Tensioner Concept

I thought of a relatively easier but somewhat sketchy concept for a spring loaded chain tensioner at 3am last night, and wanted to know what CD thought of its jank.


The spring comes from the polycarbonate mount instead of an actual spring, making this relatively easier than a regular spring loaded chain tensioner. Hopefully, this design will can create a drivetrain that can definitely last ~1.5 seasons without maintenance.

I don’t have an FRC team right now, and have neither the resources to prototype this or the math to predict it, so I have no idea how workable this is.

Depending on how you setup the poly bracket I would worry that you would kill the living hinge from the constant acceleration and stopping.

You will have a lot of issues with a bracket like.
I would recommend using a “flying star”
I couldn’t find a good picture so i tried to put it in CAD to help explain but just put a large sprocket in the middle to pull the chains apart then “ratchet” it to one end to get the desired tension

Mcmaster has a good selection of tensioners. This one’s my favorite design.

I think this would be a great solution for an after-the-fact chain tensioner on the cheap, but I would be concerned about two things:

The sprocket would tend to tilt (clear in your second picture) and would likely rub a bit on the side of the tensioner unless you used a decently thick gauge of poly. You could also turn the tensioner sprocket teeth to have a bit more of a lead-in chamfer to them to lessen the wear

Depending on the amount of movement involved, you may notice fatigue on the poly over time. Ideally you will be within the elastic portion of the materials stress-strain curve, so it would just plastically deform over and over again, but even after many cycles of that you may see some wear

With a nice thick piece of poly and monitoring of the material I don’t see why this wouldn’t work. It seems like a great, simple way to tension a chain.

To figure out what thickness of polycarb you want, you could either test and iterate, or have some fun with a simple FEA simulation.

Edit: Certain inspectors may want to see a safety guard around this as well, and you should consider this if you are thinking about using this design.

Depending on how much clearance you have between the tube and the chain, you might get better results out of bracketing the polycarb to the bottom of the tube but still having the sprocket on top of the chain run. Basically, spread out the deflection over a longer distance and decrease the angle between the tensioning sprockets and the chain itself.