#25 & #35 chains

[JohnMorenski]

ive seen posts on #25 and #35 chains before but i never saw any clear conclusion from people on what they actually preferred for drivetrains it was more just general information

and for the teams that used #25 chain did you ever have problems with it slipping under pressure? or possibly even breaking?

[Peter Matteson]

The clear conclusion we always push is to properly analyze the application and for the loading requirements on the chain. After looking at the stress that will be applied look at the manufacturer's maximum recommended load for the chain you want to use then using sound engineering judgement determine if the chain will be acceptable with apropriate factors of safety.

Don't try to shortcut this and just use something because some one on CD told you it was good. Every application should be looked at seperatly because what may work for me on the 177 drive train may not work for Robin at 173 (we rarely use the same chain size) or Andy on 716, etc.

[B Toth]

We have always used #25 chain on our drive trains. We have never had a problem with it breaking or anything. We even used it with the large CIMs from last year, and they held up through 3 competitions. I have found that #35 is too heavy and is relatively unnecessary for the robot.

[dfukuba]

This is something my team has been thinking about for a while now. (Team #8) we have always used #35 chain on the drive train in the past, it has been strong and never let us down. But i do think it might be a little overkill. I would like us to use #25 chain because it seems to be more fitting, even though we are not sure if it will stand up.
My suggestion is to try both. I'm not sure how easily you can adapt things to your system, but it you have the opportunity to try both, i would go with that. Put both systems up to some stress tests, you can even do some math to calculate your forces. You never really know how something is going to work until you try it. remember that each application is different, so if 25 works for someone else on their drive train, it doesn't mean it will work for you.

--Dan

[meaubry]

We at team 47 have used both #25 and #35 chain in various applications on the robots. Each has its own set of advantages and disadvantages. Yes, 35 is heavier, but easy access to a very wide variety of sprocket sizes is a plus.
#35 is also very forgiving as far as needing exact chain length and how to deal with chain slack, or to eliminate skipping teeth or rolling the chain off.
#25 is better when considering position sensing, it should give you a more precise method if encoders are driven by the drive system chain.
So, there are a couple more things to consider when choosing.
Both will work, just depends on what is important and what you are willing to live with.

Mike

[rockit science]

We have always used #25 chain for drive systems until last year, when we went with #35. The biggest difference that I can tell is that #35 is much less prone to "jumping off" the sprocket if you get some slack from impact or if it's not optimally aligned. Also, due to the higher stress, #25 tends to stretch more over the life of the robot, requiring more frequent adjustments. A properly designed guide/tension system will negate these issues, but adds complexity to the machine. And just for the record, we've never had a #25 chain break on a drive system. The only drawback that I can see to #35 is the added weight of the chain and sprockets. Since our machines normally come in a good bit underweight (we usually end up adding weight for ballast), this is not a problem for us. Due to the forgiving nature of #35, we plan on using it again this year.

[John Neun]

#25 chain is great, but for final drive, we learned the hard way that it is too light. We actually broke links in half at the "neck" in their cross section. B. Toth is of course right when he says to let the stresses be your guide, BUT keep in mind that the drive train sees high shock loading during maneuvering. Stresses can impulsively be very high compared to our usually static analysis. The "slow" end of the drive train is the highest chain load end, so it may pay to lighten the chain toward the motor, but be very careful with #25 on final drive. I'd love to show you the brooken pieces; I would not have believed it if I had not seen it.

Good luck!

[Richard Wallace]

Originally Posted by John Neun

#25 chain is great, but for final drive, we learned the hard way that it is too light. We actually broke links in half at the "neck" in their cross section. ... be very careful with #25 on final drive. I'd love to show you the brooken pieces; I would not have believed it if I had not seen it.

I've also seen a few broken #25 chains coming off of hard driven traction systems. Like John, I think the cause was shock loading. A #25 powertrain can be sized appropriately for stall conditions and still fail when shock loaded. Such a failure becomes more likely when load conditions get more aggressive, as usually happens during elimination rounds.

A team might ship its robot thinking that #25 chain is plenty strong enough based on practice driving at home, and continue to believe that through Thursday practice rounds. Most of the broken chains I have seen came from robots that were designed for offense, but switched to being defensive specialists in the eliminations.

[jacob07]

Originally Posted by B Toth

We have always used #25 chain on our drive trains. We have never had a problem with it breaking or anything. We even used it with the large CIMs from last year, and they held up through 3 competitions. I have found that #35 is too heavy and is relatively unnecessary for the robot.

my team came to the exact opposite conclusion. Though it may be heavier it takes stress better. The smaller chain seemed to break more then the larger chain did. If our robot was over weight due to chain weight then we lost the weight other places.

[clean399]

Team #399 has been using #25 chain for our drive systems and other mechanisms and we have had no problems that I can remember other than not being able to find a master link in our shop because it is small. We also find that since our robots come to the edge of the weight limit like last year we were exactly 120.0 pounds it saved us that little bit of weight.

[Andrew Blair]

Whoa, this seems like about the ninetieth time I've answered this.

In FIRST, more often than not, #25 is quite adequate- almost never breaking or giving problems- if it's tensioned and aligned very well. If not, you're playing roulette, and it will fail, at some point. Maybe sooner, maybe later, maybe seven times at the Pittsburgh regional in 2006.

My suggestion, use #35 from the gearbox to your first wheel, and then you can use #25 after that. If it breaks, you're still moving.

[eshteyn]

Originally Posted by Andrew Blair

Whoa, this seems like about the ninetieth time I've answered this.

In FIRST, more often than not, #25 is quite adequate- almost never breaking or giving problems- if it's tensioned and aligned very well. If not, you're playing roulette, and it will fail, at some point. Maybe sooner, maybe later, maybe seven times at the Pittsburgh regional in 2006.

My suggestion, use #35 from the gearbox to your first wheel, and then you can use #25 after that. If it breaks, you're still moving.

I couldn't agree more with your answer. We have used #35 chain on our drive system mostly because we are a great defensive robot as well as offensive. We dish out as much as we receive and we select our chain by logical reasoning. We analyze the history of playing of teams at regional events we go to as well as our calculated speed and the estimated speed of the opponent. We calculate the forces on the drive system during regular operation and impact operation and then we select our drive chains. As my physics teacher yells when he smacks his ruler on the desk "IT'S PHYSICS!!!!!!!!!!!!!!!!!!!!!!"

[b-rant]

you should have a poll but #25 I believe is the best solution for FRC if done correctly, if not you may slip.

[Superstitions]

In comparing the chains for our arm we are trying to find out how much #35 and #25 weighs per foot. Googled it and could not find the specs. Maybe someone who has a scale handy could weigh 10 feet of it.
Thanks, Jeff

[Richard Wallace]

#25 -- 0.09 lb/ft

#35 -- 0.276 lb/ft