Can someone tell me what the calculations are for determining the choice for roller chain? I am guessing the terms you use are the maximum working load and average tensile strength but how do you calculate what that is going to be in the robot.
Adam,
In its simplest form you need to calculate the torque at each sprocket and the find the resultant force on the chain. For example if you have a torque at the sprocket of 2000 inch-lbs and have a 4 inch pitch diameter sprocket, the force at the pitch line on the chain is 2000/2 = 1000 lbs. Since we like to have a safety factor of 2-3 than you would select a chain size with a breaking load in the 2000-3000 range minimum. #35 falls into this range. The load needs to be calculated from the direction that is applying the greatest force. For the drive, the wheels generally slip before the maximum torque of the motors is achieved. A lift mechanism may get jammed or try to lift an immovable object, the torque in this case is from the motor side.
Word of caution, sprocket teeth can also break. Try to use a sprocket with as many teeth as possible, the load is shared by each tooth so the more the merrier.
What is the differnce between double pitch and single pitch roller chain?
Double pitch roller chain has a pitch twice as large as single pitch equivlant chain. A double pitch chain should have the same strength as it’s ansi equivlant, but weigh less because there are fewer rollers (note that a chain’s pitch is the distance between rivets).
Thats the best I can do without a picture, you might try searching chain pitch on google.
Greg
(edit: for readability)
Since we like to have a safety factor of 2-3 than you would select a chain size with a breaking load in the 2000-3000 range minimum. #35 falls into this range.
According to Mcmaster:
Working load is the maximum load capacity that can be applied to the chain under normal operating conditions. Average tensile strength is the average load capacity at which the chain will break
Never mind I just answered my own question. Now what will happen if you constantly run the chain over the work load but under the break load?
Thanks for the help.
Essentially, it’s longevity will decrease, and it will eventually break. Chain (like any component) has a finite service life. Often times, chain isn’t designed with sudden stops and changes in direction in mind. On the last leg of your drive train when you’re connecting sprockets to wheels, just play it safe and go with #35. 
Matt
All right that is not a problem. Since the chain I am looking for only is sold at #40 and above. Though I wonder if using it as a tank tread will change anything. It is called ANSI attachment chain.http://www.mcmaster.com/
I guess I’d like to see what you’re going to do with it… those links are so darn expensive! In addition, #40 chain is one heavy hunk of metal. However, I’m curious to see what you’ve got in mind.
Matt
I guess I’d like to see what you’re going to do with it… those links are so darn expensive! In addition, #40 chain is one heavy hunk of metal. However, I’m curious to see what you’ve got in mind.
I read a book that suggested using the attachment/conveyor chain as a tank tread. More specifically I want to use the chain with the flat attachments. I thought that by bolting on neoprene rubber inbetween two chains it would make a nice (abeit expensive and maybee heavy) tank tread. At it’s cheapest it would be 7.00 a foot which would cheap enough for me. Mcmaster also is not know for being cheap.
We used attachment chain from Diamond Chain for our 2002 Robot. We riveted steel cleats to the chain, which were narrow enough to allow the drive to turn, but dug into the carpet to provide pushing force.
FIRST outlawed metal cleats in 2003, so I can see why you are thinking about putting rubber cleats on the attachment chain. We actually tried doing this in 2003, with urethane cleats. We aligned our wheels, kept the chain unbelievalby tight, and we STILL threw our chain off. The urethane does no allow for turning as well as metal cleats do, since they were wider and stuck to the carpet better than metal.
I am not saying that this rubber cleated chain drive system cannot be done, but I am saying that it will be risky and tough to make it work. Rubber likes to stick to carpet and chain likes to fall off of sprockets at the slightest side force, as it’s moving… so be careful in how you design your tensioning system and wheel alignment system. Don’t skimp on those two features. Ensure that your wheels get aligned and create a separate tensioning device to get maximum tension on the chain.
Good luck,
Andy B.
I agree with Matt’s recommendation to use #35. Some people think its overkill but I’ve seen the lighter chains break under impact often enough to not want to use them.
One additional (and I think very important) advantage to #35 chain is that it is less misalignment-sensitive than the smaller chains (1/4" pitch or 8mm pitch). This alone is a great reason (imo) to use #35.
Ken
And though this is sort of off topic, since the question has already been answered, I’d still just like to throw in my four cents about #25 chain ahead of time.
Someone is going to say this. It’ll be during week 2 of the build season, and a rookie team will ask for advice on chain in these forums. 40 people will reply, many of them like the above.
The truth is that there have been instances where #25 chain has broke on some teams’ robots on the last leg of the drive train. Since the forces are relatively the same for about every team (and the only way to reduce this is by having poor traction or big sprockets) it’s definitely in the best interest to not cut weight in something as critical as your drive train.
In addition, #25 chain will stretch significantly more over the course of the competition, and misalignment is not fun, as Ken has said. Let me be clear: chain stretching isn’t a fun problem! Nobody gives high fives or a does a fancy FIRST dance because of chain stretching.
And numerically… I don’t understand how or why it happens either, but it does. It’s probably a dynamics forces thing. Every year there are teams that have #25 chain break on them. It’s an extra couple pounds to ensure NO worries about this problem occur. It’s well worth the weight to save on what could be competition altering failures.
So… there I go being blunt with a person that doesn’t exist… If you disagree… I’m jealous of the 2 lbs you’re saving this year.
**My Advice: **
#25 chain on the last leg of your drive train - Don’t Go There.
My 4 cents,
Matt
I am not saying that this rubber cleated chain drive system cannot be done, but I am saying that it will be risky and tough to make it work. Rubber likes to stick to carpet and chain likes to fall off of sprockets at the slightest side force, as it’s moving… so be careful in how you design your tensioning system and wheel alignment system. Don’t skimp on those two features. Ensure that your wheels get aligned and create a separate tensioning device to get maximum tension on the chain.
Would idler sprockets be ok in tensioning the drivetrain? Also would using a high durometer material lower the traction of the belting?
OK Matt, I’ll bite! We have been using #25 chain for many years on our drive system. Ask anyone if we ever broke down because a chain broke. Last year we even used #25 chain for our wings and that never broke even though I thought I had designed it “on the edge.”
Here is my real point: Noteworthy engineering is about making the proper trade offs in an intelligent way to maximize the efficiency of your design. To flat out say that one should never use #25 chain on your final drive is not appropriate. It is no different than saying that you should only use steel for your frame because aluminum bends too easily.
If you are careful to design your system such that it will not see significant dynamic loads, you can use #25 chain and not ever see a problem. Without getting into too many details, that loading depends on your gear ratio, coefficient of friction and a few other things.
Besides, in some cases, you prefer to have this “mechanical fuse” as your controled breakage point. As an example, depending on your design, you may prefer to fix a broken (or stretched) chain rather than a transtorque coupler or a keyway.
To answer Adam’s original question about what happens if you run chain above it max working load but below it break load - it stretches gradually.
Raul
I am telling you now that #25 will and does break. Last year we continuously broke our chains. In one match we broke 3/4. I was told in 9 previous years we had never broken 1 chain. The difference is we went from 4 motor drive to 6 motor drive. The additional HP was too much for the chains. This year #35 will be our chain of choice.
Of course #25 chain will break, and so will #35 if it sees a high enough load. All I am saying is that you should have a good reason to make something stronger. Let’s not just make declarations on this forum that one should never use #25 chain!
I have seen many teams start drilling holes all over the place because they are over weight. In the meantime, they have gears that are 1/2 inch thick that weigh a pound a piece and #35 chain driving wheels that have such low traction that there is no way they could ever load the chains or the gears enough to justify such overkill.
If you simply do not have time to do the math and can spare the weight, then fine, over design it. Or, if you have done the math and have determined that #25 will not work for your application, then by all means, use something stronger. But don’t ask everyone else to just give up and play it safe - they also need to determine if it is an issue for their application.
You can be extra safe or you can be competative - its your choice.
Raul
I agree that every team MUST assess their own needs and design. I am sorry if it sounded like we have the only answer. This year we will change because of last year but the previous years we had no problem. Weight is each teams biggest challege. Every team could go overweight without blinking. Good teams plan ahead and assess needs before building and finding they are 15 Lb over-weight. It is much easier to add to a robot design than remove to make weight.
Good catch Raul, I don’t mean to push thoughts as fact. Thanks
Rar! 
I love that firey “extra safe or competitive” statement. Haha.
First, I agree it’s bad to declare to NEVER use #25 chain, it has a lot of good applications. (Fortunately, I don’t really Raul was quoting me, since I merely adviced to not use it on the last leg of a drive train.)
Second, I’m really glad that Raul did “bite” and say something. You’re on a team that’s used #25 with great success for a while now.
Something to consider, though I may be incorrect, Wildstang has typically been using #25 on crab drive style systems, which has typically used short chain lengths interacting with only one wheel per length of chain.
In addition, 111 has been designing (very awesome) strategically fast and defensive robots, not the “fierce, head-on, pushing on the carpet with 2.5 coefficent of friction for 2 minutes” sort. 111 has designs that I would to consider to carry atypically smaller loads on chain. It is a much different situation than a tank drive style system which may have one continous length of chain for two wheels per side at 6 feet per loop. As has been said in similar threads, proper tensioning and load calculations are critical to use #25 chain, as well at continuous “stretch management”.
Here’s some reworded suggestions:
- If you’re coming on these forums because you’re unsure about whether to use #25 or #35 chain, and unsure about doing calculations to determine the loads for your applications, I sincerely suggest you you don’t give yourself unneccessary headache- it’s a few pounds to sleep better at night, go #35.
- If you’ve been around for a few years and are thinking of going down to #25 to save weight, use short lengths and do careful calculations on load.
- If you’ve had #25 fail on you, work on improving your load handingly methods, or just realize that #35 can be your friend.
- If you’ve been around for several years, you’re probably not looking for advice, so contribute some like Raul did.
More cents…
Matt
Okay Raul… now I’ll bite…
I agree with EVERYTHING you said, except this above statement.
In my experience (not nearly as extensive as yours :)) in this competition "extra safe" IS competative. To argue that the choice is limited to one or the other seems dangerous.
I would urge everyone in this competition, especially rookies to “play it safe” and not to walk on the razor’s edge when designing their robot. It’s the same as with drivetrain speeds… “Sure, you might want to be an extra foot/sec faster but what good is it going to do you when (the planets misallign and) you pop your breaker?”
Sure, 1/4" chain weighs less, but the phrase is “better safe than sorry”. I would advise most teams to “spend the weight where it matters”.
You can have the most elegant mechanism in the world, but it’s no good when your drive is dead, and it’s doing semi-circles across the field. I’ve seen this happen to the BEST of teams, and I’ll tell ya… probably 80% of the time it’s a #25 chain which blew off it’s sprocket.
It’s not usually a loading issue, so much as a misallignment issue. As mentioned above, #35 is MUCH (MUCH!) more forgiving when it comes to allignment.
So yes… I agree with Raul…
Analyze everything, have numbers to back up all your decisions, and don’t just “Take someone’s word on it”.
But… also ask yourself if one extra factor of safety would be in your best interest…
Safer IS better.
John
PS - Raul, if you haven’t had any #25 problems… then all I have to say is: “I sure wish I could build em like Stang does!” (I guess I say that anyways… such beautiful robots…) 
I know that #25 can work. We used in many many years with no problems that we didn’t cause ourselves.
But… we had to spend a lot of time thinking about how to make the chain work right for us. We put designed in robust tension systems. We paid close attention to alignment of sprockets. Etc.
Last year, we went to #35 chain because frankly, we were not confident that we had the ability to make it work for us given our level of resources last year.
Based on what I saw, in the future, I will use #35 chain in almost every case over #25.
#35 chain is SO much easier to work with. From alignement, to tension, to abusive loads, #35 will let you get away with many more sins before it damns you to hell.
So… …that is where I come down at least.
Joe J.