Originally Posted by DampRobot
I have yet to see any really good explanations of chain stretch. That doesn't mean no one understands it (if someone does, please jump in!), but that for the most part the FRC community is interested in phenomena instead of root causes. (Never use scissor lifts, never use steel, always active maintain control of game pieces, etc. are examples of phenomenological "rules" in FRC. We are usually content with fuzzy understanding of the physical motivation behind things we observe to be true. Before anyone gets super mad at me, I'm pretty guilty of this too.)
From my experience, chain stretch has three components. One dominates over the short term, but is dominated by the other two effects over the long term.
First, there can be actual physical stretching in the chain, in the sense that there's some very large spring constant to the chain. You can probably stretch chains just a tiny bit as you're putting them together, but barring any extreme loading, this is a very small amount.
Second, the chain itself will wear over time. Grease in the tiny bearing surfaces in the chain links will dry up, and the chain links will physically wear so that the link to link distance increases very slightly. Unlike component one, this is a long term effect, and isn't reversible.
Third, the sprockets around the chain will wear. This doesn't have anything to do with the chain itself, but will manifest itself in the same way. Over time, the steel chain will wear aluminium sprockets, and the chain will become looser as the sprockets become very slightly smaller. In the absence of hard evidence, I would guess that this is the dominant effect behind long term "chain stretch."
In any case, I can't see a way in which a c-c design would stretch chain any more or less than a tensioned system set to exactly the same tension. The only difference is how you compensate for the stretch. In a sliding bearing block system, you just re-tension and you're good to go. In the case of c-c designs that asid was talking about, the wall of the tubing retains the chain, which keeps it from coming off or ratcheting on the sprockets, which makes the stretch less of an issue.
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