chain in tube experiences

We’ve never had this issue in 3 years of chain in tube with 16T sprockets. I expect the chain would break LONG before it “stretched” enough to do what you’ve described.

Chain in tube is definitely not the most fool-proof way of building a drivetrain for FRC* but, when done properly, is no less risky than a classic WCD setup.

*buying the kitbot is

To answer the question, though, chains do wear in and additional backlash does occur throughout the season. Like you said, this is mitigated by direct driving one of the wheels. We did notice increased backlash throughout the season in our CIT, but it didn’t affect our 2-cube auto consistency. You’d most likely notice the affect if you changed direction frequently during auto.

IMPORTANT NOTE: “using the floor and ceiling of the tube to keep the chain from skipping” is not what you should be doing in CIT. The floor and ceiling of the tube should never be relied on to keep the chain on the sprocket. Proper center-to-center distance between sprockets and proper alignment is all that is needed. We usually run a C-C distance that is a bit larger than the mfg recommended distance, but how much larger depends on the type of chain and the sprockets used.

Less important note: We installed the chain in the tube for 2018 and never touched it for the rest of the season. During the offseason, after our robot competed in the 2nd most matches in the world, we took the drivetrain apart for a post-mortem and hadn’t even worn through the anodized coating on the 16T VexPro sprockets. In fact, one of our drive gearboxes literally fell off the robot before we’d put any wear on our drive sprockets.

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