#25 Chain Information

[David Guzman]

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

[clean399]

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.

[Jeff K.]

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.

[Mr.G]

Working load for #25 is around ~150 lbs depending on the brand.
Working load for #35 is around ~500 lbs depending on the brand.

[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?