#25 Chain Information

[Ted Boucher]

Team 237 uses a combination of 35 and 25 chain on our drive system. 35 chain from the transmission to the center driving wheel, and then 25 chain to both the front and back wheels. Just make sure your chains are straight, mostly protected, and tightened, and you will be good.

As for the ways to tighten, you do not have to make your chains the perfect size, as the season goes on, the chains can stretch, and only create problems. On 237, we make the chains have a little slack and we make a simple chain tensioner. This is made out of a 3/4" round piece of round delrin plastic, and drill a hole that is offset from the center. This is helicoiled for a 1/4-20 screw and set in line with the top of the chain in the drive system. Since it is offset, the piece can be rotated into the chain, and the chain will tighten and ride the delrin. This allows for an easy tightening at competition and easy maintenance when you have to change wheels and such. If you need pictures of this, PM me and I will be happy to help you.

In the past 2 years, we have never broken a chain, and only have lost 2 master links due to freak occurrences with a foreign object

[sanddrag]

Keep it well aligned, well tensioned, and use sprockets in the 16+ tooth range and you should be fine.

[Brandon Holley]

our team has spent almost teh entire preseason debating this issue and we have put forth a lot of effort in actually calculating the strengths of the chains. ill get the information and post it on here shortly because its really good qualitative stuff.

[jackie Ha]

I know my team has used #25 chain for the past 6 years, and we have not encountered many problems with it so far. As far as keeping the chains tensioned, heres a thread on how we do it. http://www.chiefdelphi.com/forums/sh...ain+tensioning

Team 114 has used chain on all our primary mechanisms for the last 4 years, and we have never had any problems. The stuff is strong enough, as long as you design your mechanism correctly. Always allow for adjustable tensioners, and never overtension the chain. If you do that, it will be more than strong enough for any FIRST use.

[sanddrag]

Originally Posted by 114ManualLabor

If you do that, it will be more than strong enough for any FIRST use.

Go back to 2005 and ask 968 that. "any" is a pretty strong word. But, "many" is definitely true.

As long as you're designing mechanisms to transfer force correctly, there shouldn't be enough force to break the chain. However, I am only speaking from my experience, so if I'm entirely wrong, correct me. It's the best way I learn.

[Travis Covington]

You need to design the system within the limits of the chain. For us, with a few of our drivetrain gearboxes, we were exceeding the maximum reccomended working load for the chain, but were still under the chains breaking load - just barely. We have tested it thouroughly enough to know that there is an obvious safety factor in the chain manufacturers quoted numbers, and as a result have designed our systems carefully enough around that, knowing one small misalignment or potential impact during a match could mean we break a chain. We take that risk, at the benefit of reduced weight and size. It is a fine line to walk, and you have to consider everything before you make that decision yourself.

Transfering 'force' should be clarified, too. #25 chain would probably transfer some force in this picture below just fine, however, the massive reduction in the gearbox means that as soon as you put any sort of 'real world load on the system, the chain will simply fail. The amount of force you wish to transfer has everything to do with what size chain you need. Below, we almost needed a chain larger than #35, but again, we figured if there was some sort of impact or collision during a match, we might actually prefer the chain break rather than the arm or frame of the robot itself.

For drivetrains, it's worth running the numbers every year just to be sure that #25 will work. You can calculate this quite easily. 2 cims at 2ft/s would be safer with #35 chain in my book.

[techtiger1]

Thanks to everyone for your input on this subject. I was wondering if you all could post some of the locations were you purchase your #25 chain and sprockets. 1251 is working on a few new ideas so your opinions and suggestions are much appricated on this subject. Finally, out of curiosity, the person who posted about the load numbers on 25 Vs. 35 chain were did you get those numbers?

Thanks,
Drew

[Tapoore]

If you only need very short lengths of #25 chain, the Electronic Goldmine sells it in 23" lengths for $2.49 each (they come with a master-link too). If you need longer lengths of chain or some #25 sprockets, McMaster is probably your best bet.

[RTTComanche17]

One thing to watch out for with all chains (esp. the #25) is the masterlinks. Of the five or so chains that i have seen broken, four were because the masterlink had been improperly installed or had grown weak from being taken off and reused too many times.
We have used #35 chain for everything and have never had a problem. Last year our robots speed was around 2 fps with two small cims per side. Our frame was bent in all the smash 'em' up bang 'em' up stuff and rubbed our drive chains, but they held up like champs. We out-pushed everyone we met last year, at regionals and in Atlanta. When in doubt, go stronger. We will never use #25 chain. Why chance it?

[Cuog]

#25 chain is nice and light, it was still strong enough for us in 05. The problem is that getting more in a hurry is a problem since it isn't used as much in FIRST. Also its smaller and you have to use a different chain breaker and the master links and half links are a royal pain in the...

Other than that if you don't mind the extra effort of using the chain and the lower number of available sprockets you will be happy with its weight savings.

[David Guzman]

I want to thank everyone for their input. We will be making a prototype with 25 chain and seeing how it goes. We are going to most likely use wedge top as our material of contact with the carpet (or w/e it is) and according to what you guys are saying the rubber should spin before the chain breaks. Also our gearboxes are not "over designed" so we rather lose chain than damage the gearbox by having the strong chain (thanks for pointing that out)

I am glad to hear so many good comments about 25 chain because I wasn't sure, but it definitely sounds like worth a try.

It will be great if people who have more information on this chain can keep posting it as it will be helpful to my team and I am sure many others.

David

[ahecht]

Theres another thread with lots of tensioning ideas at http://www.chiefdelphi.com/forums/sh...474#post249653

[JoshuaFreier]

One additional bit of information our team has found over the past six years of working with #25 chain is you must do a better job aligning the sprockets then you do with #35. #25 chain is much less forgiving in this regard.

Have Fun,
Joshua