Quote:
Originally Posted by RoboChair
I would not use #35 chain for pretty much anything on a robot, it is heavy and way stronger than it has any business being on a drivetrain. Working load(not breaking strength) on #25 chain is 88 pounds vs. 199 pounds for #35.
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Honestly, I often see the tradeoff between #25 and #35 chain in a drive train application severely underplayed here on ChiefDelphi. The truth is there are pros and cons to each, and teams should evaluate which size chain they use.
It is not uncommon for a robot to weigh 150 lbs with a battery and bumpers and then have a CoF on their wheels of 1.2. That means you'd have 180 lbs of tractive force or 90 lbs per side of your drive train. If your sprockets have a pitch diameter of approximately 2 inches and you have 4 inch wheels, that's up to 180 lbs of force going through your chain! Nothing close to this will usually happen on a WCD in most cases because the center wheels will likely be direct driven and carry the majority of the tractive force, but this depends on your CoG.
#25 Chain Pros:
-Lighter Weight (~1.0 lbs/foot)
-Takes up less width
#25 Chain Cons:
-May require tensioning (higher part count)
-Co-planar sprockets are more critical (more precise machining)
-May come close to pushing limits (have to do the math)
#35 Chain Pros:
-Can probably get away without tensioning (lower part count)
-Sprockets less sensitive to axial position (less precise machining)
-High safety factor on chain working load
#35 Chain Cons:
-Heavier (~2.5 lbs/foot)
-Takes up more width
For the top teams, the extra 10-15 lbs you'd be saving by going with #25 chain is well worth it. These teams have no problem getting their sprockets co-planar sprockets and have experience doing the math to see if they're doing anything risky. On a WCD, the direct drive of the dropped center wheels off of the gearbox reduced the amount of the force that will be in the chain. For teams that may benefit from a lower part count, might have difficulty making co-planar sprockets, and deem the peace of mind of something that will "just work" to be more valuable than the weight savings, an argument can be made for using #35 chain.
I'd estimate that for about 75% of FRC teams, if they were to use chain they should at the very least think about these tradeoffs. What works best for the best teams in the world may work best for them as a direct result of their goals and resources, while it may not necessarily be the blanket best solution for all teams across FRC.