I searched the forums and didn’t find too much about 25 chains. I am considering the usage of this type of chain on our 07 bot and was wondering what the experience of other teams have been.
To be more specific I want to know how strong it is for drive trains. Would treaded robot with 2 small CIMs per side going at 2ft/sec break this chain when stalled? I would like any info knowledgeable people have abbot this chain.
Thanks in advance
Our team #399 has been using #25 chain for the past four years and have rarely broken a link you just have to use the right amount of chain to where you have no slack which means you may have to use half-links. We have used it for our drive train and it works and saves us quite a bit of weight.
Depends on the coefficient of friction of the wheels to see where the wheels would slip during competition.
I would imagine that the chain would most likely break if your low gear is only going at 2fps, and you had a mechanical failure in which the wheels would get locked.
But in a more realistic view, as in during a match, it depends on how much force requires your wheels to slip in a pushing match. If that force is greater than the breaking strength of the chain, then you just might have a problem. Also, see how much torque is being output out of the gearbox, and taking the pitch diameter of the sprocket into consideration, see if that force is greater than the breaking strength of the chain. That would be in a worst case scenario like that mentioned above if your wheels got locked and your motors would be at stall, giving maximum torque, and maximum damage to motors.
Hope that helps.
Good luck in the coming season.
Also:
When determining the chain length, like Ted said, it would be a good idea to add a little slack and tension it with either an idler, or if you’re going with a custom chassis, having a slotted part for the wheel mount so you can tension it. 254 and 968 have done it in beautiful ways. We’re experimenting with another way, such as the attached image.
Working load for #25 is around ~150 lbs depending on the brand.
Working load for #35 is around ~500 lbs depending on the brand.
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
Keep it well aligned, well tensioned, and use sprockets in the 16+ tooth range and you should be fine.
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.
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/showthread.php?t=50318&highlight=chain+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.
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.
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.
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
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.
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?
#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.
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
Theres another thread with lots of tensioning ideas at http://www.chiefdelphi.com/forums/showthread.php?t=27474#post249653
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!