Assuming the use of a chain break tool and no master links, what are the advantages of using bicycle chain instead of #25 HD? Is it really worth the machining work that would have to be done to make the sprockets interface with typical FRC stuff?
Bicycle chain and sprockets are often free or near-free if you know a bicycle shop and don’t mind getting “worn out” material which will be completely fine for ~4hrs of use in FIRST. Front sprockets aren’t bad to adapt hubs and mechanisms to, and an old derailer can take up slack; a rookie team I knew used free bike parts on their 'bot a few years back.
Cost is pretty much the only benefit; there’s no guarantee that the tensile strength will exceed #25H (yes, it’s “bigger” but test it or cite a datasheet before making claims about rusty used bike parts), and it’s designed to skip between sprockets easily, which isn’t a plus for us.
Yes, there’s a significant amount of craftsmanship to make it work with “typical” FRC stuff… or you can take an old kids bike frame, flip it over and bolt it on your kitbot, use the bottom bracket to pivot an arm (end effector bolted at the pedal), and grind off anything you don’t want. A COTS pivot+sprocket assembly is definitely not against the rules.
You won’t look like the Poofs… but it might well work!
The bottom line as far as I am concerned is that bicycle chain doesn’t interface with standard FRC hardware. If you’re willing to do the work to make it happen, go for it!
IIRC, (some) sprockets are designed to let the chain skip, not the chain itself. If you get a sprocket designed for a 1 by/single speed, it shouldn’t be a problem.
The biggest issue I see is that bicycle chain has a pitch of .5" which is greater than the .375" of #35 chain and much greater than the .25" of #25 chain. There wouldn’t be many teeth meshing with the chain, at least in a west coast drive. We’ve never done it before but that would be my concern.
No, it’s not worth it.
Between #25HD and #35 you have plenty of FRC specific COTS options that are great.
Using bike chain is solving a non issue at great time expensive.
Save your team’s bandwidth for problems that will make your robot better.
We ran #25HD on our WCD—drive train last year, and didn’t have one issue through over 100 matches.
Not to nit pick but 4 hours? I hope everyone has the chance to or is at least putting effort toward driving their robot for more than 4 hours (especially now with no bag). No idea how driving 4 hours vs 40 vs 400 impacts the use of used bike parts.
If you use 25 chain and show up to a competition, everyone and their mother can help you with spare parts and alternate options to upgrade and repair.
If you show up to a competition running bike chain, you are completely on your own should anything happen.
The effort needed to use bicycle chain is probably not worth it in terms of competitiveness, but it has a very high coolness factor. Case in point over here. Coolness shouldn’t really matter in competition, but it makes it easier for me to remember certain teams.
Thanks to all for some really good and varied responses. A team that I work with in our region has used bike chain on their drive trains for at least the last several years and had at one point offered to help us do the same, machining the sprockets with us at their shop. They’ve had great success with their robots, and I wanted to weigh how valuable this would be for us to devote resources to. I think we will stick with #25HD for our 2020 robot and off-season work.
Heading into Championships this year, our competition robot had about 3 hours of runtime on it. The practice robot was closer to
700 460 400? Now I’m not sure. 4 hours is not a bad estimate of how much time a robot will see on the field over a season.
From a mechanical engineering perspective, 4 hours and 40 hours are practically identical specifications. A bicycle chain get can ridden for over 1000 hours before an ordinary bloke will replace it; an old chain that had another 4 hours in it will also be fine to 40.
I find quoting 4 hours for FRC applications helps junior designers be ambitious enough about weight reduction (using 1/16" boxbeam, plastics, rivets, etc) without forgetting that if it’s starting to break while they’re testing it in the lab in the first 30min, something’s gotta change. And reminding us that if it breaks in 8 hours… we can remanufacture it at the same weight.
The only mechanism that might get over 40 hours of operation without design changes & maintenance is the drive.
(400 is unrealistic, my most dedicated students are only in the lab for about 250 hours (and the median is closer to 120 hours), I don’t think a chassis could be driving for more than about 150.)
teach me your secrets
700 hours? Or 70?
By the end of the season it was broken in every possible way. Aluminum brackets snapped, chassis bent, cable chain flopping uselessly, wires torn and rerun, gears worn down, and every part was loose. My secrets? Trash the thing.
That was napkin math that I did months ago. I just redid it and got 460. Is “mid 3 digits” a more acceptable guess?
Edit: the other assumption I’m making is that it’s being driven for all of the time that the drivers and programmers had it, which is questionable at best. It’s not counting the 4 weeks where the chassis was complete and being used, but the manipulator wasn’t. I don’t know how those two factors balance out.
359 has more blue banners then 973.
We’ve got three that are a little more blue.
But what’s that got to do with the price of tea in China? How many banners have #25 chain won?
359 (as far as I remember) uses bike chain because it’s more readily available in Hawaii, not because it’s better than #25 or #35.
359 doesn’t even use bicycle chain anymore
Last I checked, HoF was the bluest banner. 359 1, 973 0.
Now, I would tend to agree that using bike chain isn’t necessarily worth the effort it takes–but that may depend on if it’s a major undertaking to get 25HD or 35 chain. If it is a major undertaking, then it becomes an engineering tradeoff, and we all know how those go… Doesn’t matter which way you go, somebody complains.