#25 Chain Information

[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

[Kit Gerhart]

We have used #25 chain for years for our 6WD drive train with good reliability. The chain itself is very strong, like 700+ pound breaking strength, and is, of course, much lighter than #35 chain. Also, it allows us to get more reduction between the transmission output and the wheels than is possible with larger chain.

Good alignment is much more important than with #35 chain, and you need to have adequate wrap on smallish sprockets. We use a single chain around a transmission output sprocket, a tensioner, and the three wheel sprockets. Some of our machines have had only about 90 degrees of wrap on a 19 or 20 tooth transmission output sprocket, and the chain needs to be pretty tight or it can slip, not a good thing. The bottom line is that #25 chain will work for most applications on our machines, but everything needs to be more precise than with larger chain, including sprocket alignment, lack of wobble, and lack of runout of the sprockets.

[Andrew Blair]

I'd like to stress that, as Sanddrag and Travis pointed out, proper alignment and tensioning is crucial. We've used #25 practically forever, and had great success- and failure. #25 is almost entirely suitable as far as FIRST goes in terms of actual chain tension loading. What the motors put out, stopping and starting forces- the chain can handle the tension forces well.

However, #25 will quickly inform you if there is *any* misalignment, angular or lateral, mis-tensioning, or other problems. Last year, even with properly tensioned, aligned, and lightly loaded chain, if we ran over a ball, we crossed our fingers!

Regionals can be a humbling and frustrating experience should you screw up- mechanical reliability is paramount, and badly implemented #25 *will* cause problems there. We broke ~6 chains at Pittsburgh last year, and paid the price. Limping robots are bad robots. However, we tensioned and protected the chains better, and had a great success rate.


As Travis said, you must evaluate each case individually and weigh the consequences. You save huge amounts of weight using #25, but it's very important to design the system well. It will not hold up to running barriers over, or rubbing against a bent frame, or dealing with the mis-alignment caused by that bent frame. But I don't want to get too down on #25; we love it! It saves so much weight, and when properly implemented, won't give you any headaches. Just be careful!