#25 Chain Drive Experience ???

[Joe G.]

We did this for the first time last year. Chain stretch was pretty dramatic, more than our tensioner designs could handle, though this was just as much a function of bad tensioner design, as it was increased stretch from the #25. I think we ended up having to pull a link about 2 or 3 times per chain over the course of the season.

Additionally, we made the mistake of using #25 chain without precision turned spacers. We used spacers cut from sheet stock which got the dimensions "about right," to a degree which would have been acceptable for #35. "About right" wasn't enough, and we threw a lot of chain due to sprockets not quite mounted in the same plane. Finally, we used smaller sprockets than we needed to, which increased load felt by the chain, and reduced the slack needed to throw it. We never had a break or throw which looked consistent with overloading the chain, and it should theoretically never happen with the loads experienced in a typical FRC drivetrain, but I'm sure this intensified the other two problems.

I know of many success stories as well, and I'm pretty confident that we could have made it work with better tensioners, bigger sprockets, and more precise spacers. But the experience left a pretty bad taste in my team's mouth about the whole thing, and we're likely going to be using belts instead next season. More upfront design work required, but much lower maintenance. There are advantages to #25 chain; that's why a lot of very good teams use it. But proceed with caution.