#25 Chain

[JamesCH95]

Originally Posted by PayneTrain

I believe if you are running the 7.56" wheels in a total reduction that gets you 6 fps, I think that operates outside of the recommended range of #25 chain. We've been fine with it this year after beating up three different robots with it over the last 7 weeks but we are running a single speed north of 12 fps on 22T sprockets.

The recommended working load of #25HD is around 90lbf. This is fine to exceed for shorter lifespans, but with the tiny sprockets teams are running this year...

In round numbers:

8in wheel diameter
2in chain wrap diameter
µF = 1.3
Robot weight = 140lbf

Assume:
All weight on one wheel (possible, if not likely, during defense crossing)
Drive is traction-limited (certainly the case at 6ft/s with 3 CIMs per side!)

Chain tension:
140lbf*1.3*8in/2in = 730lbf

Breaking strength of #25 is around 780lbf, giving one a FoS of 1.1, and virtually guaranteeing yielding in the chain.

This case is quite conservative, but being conservative in drive-train stress considerations is probably a good idea.

For consideration: in our chain-snapping 2016 drive train the calculated tension was 550lbf. Changing to #35, with a breaking strength of about 1900lbf, did the trick. In prior years we've had chain tensions in the 150-200lbf range. Having a FoS of 3+ versus chain breaking strength is probably a good idea.