Chief Delphi - #25 Chain

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Quote:

Originally Posted by GeeTwo (Post 1589959)

The lengthening due to wear of a chain is calculated by the following formula:
% = ((M- (S*P)) / (S*P) * 100

M = the length of a number of links measured
S = the number of links measured
P = Pitch

Green, Robert E. et al. (eds) (1996), Machinery's Handbook (25 ed.), New York, NY, USA: Industrial Press, ISBN 978-0-8311-2575-2.

Quote:

Originally Posted by GeeTwo (Post 1589959)

Does anyone have any good info on how much #25 chain stretches over time? As chain stretch is actually wear of the roller axes, it will presumably plateau after a break-in period. That is, once it has stretched, what is the effective pitch length for the free runs between the sprockets? 0.2501"? 0.251"? 0.26"? 0.27?"

Has anyone ever tried "pre-stretching" chain as an alternative to dynamic tensioning? If so, how much tension and time is needed to get on that plateau?

That seems like some extremely interesting information that might not exist at this point. I wonder if someone with access to a good tensile testing machine (like a University) could do some tensile tests on lengths of chain. That would yield both theoretical data if you pull it till the chain snaps, and practical data if you used a max load that might be something you'd see in FRC applications.

Basically, I would love to spend a day with #25 and #35 and a big hydraulic tensile testing machine.

Chain doesn't stop stretching (roller axes don't stop wearing), but it does plateau after a little bit. Teams have tried pre-stretching chain before, but you want to actually run the chain while doing this, not just pulling on it or whatever, since chain stretch is really the pins wearing down. Not as simple as linear force + time. There's also some sprocket wear that can be a factor in chain tension.

We abused #25 chains and sprockets this season. During design and assembly, all looked good and worked smoothly.
The 8 wheel cantilever axle design was extremely hard on the bearings and the 2x1x1/8 aluminum chassis tubes. After a day of qualifying at Alamo, the axles had excessive axial and lateral clearance. The bearings were no longer tightly fitting in the chassis tubes, causing a wee bit of chain/sprocket alignment error. We ended up letting our alliance down in the semifinals as we had destroyed chains and sprockets. (sorry about that)
The first step towards a fix was to replace the C-clip axle retention design with an end bolt design. This allowed for a preload on the bearings, keeping the axles parallel to each other and the sprockets aligned nicely. We also started replacing all of the chains and sprockets after qualifying. Future drive systems will not need this kind of maintenance.