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Originally Posted by JVN
I think most teams that have trouble with #25 chain, don't actually exceed it's tensile load strength, but in actuality just throw it off the sprockets.
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Woburn in 2003 was an exception--the #25 chains, though tensioned correctly, were used with too small a drive sprocket (18 tooth, if I remember correctly), and too powerful a gearbox (3 motors each, approx. 2.8 HP total, before efficiency losses). The individual links stretched to failure, probably as they were passing around the drive sprocket. It's unknown whether the rigid idlers further stressed the chain.
For information on the proper use of chain at various speeds and horsepowers, with various sprockets, consult
the Tsubaki Chain catalogue, specifically
pages A-1 through A-7 (Acrobat pages 12-18) of Section 1: Drive Chains. There's a chart which will allow you to determine whether the design you're working with needs #25 or #35 chain.
Let's just say that the 2003 Woburn drivetrain performed exactly as Tsubaki predicted...we had doubled the acceptable maximum power for the chain. 13 broken chains later, it was decided that the next robot would probably need to use #35.