#25 Chain Drive Experience ???
 

Just wondering what everyones experience has been with the use of #25 chain between the middle and outer wheels of a 6 wheel robot (ie 2 loops of #25 chain on each side of the robot). I'm hearing different stories and have seen broken robot #25 chains being changed on the field right in the intermission between finals rounds. I also hear it will stretch substantially more than #35 chain. I know 1310 has used it in past but was using #35 last year.

Also, anyone confirm that #35 chain in the above configuration doesn't stretch much at all, any slack accumulated appeared to us to be caused by wear on the aluminum sprockets (ie the slack remained even after replacing the chain with brand new chain).

Re: #25 Chain Drive Experience ???
 

We did this for the first time last year. Chain stretch was pretty dramatic, more than our tensioner designs could handle, though this was just as much a function of bad tensioner design, as it was increased stretch from the #25. I think we ended up having to pull a link about 2 or 3 times per chain over the course of the season.

Additionally, we made the mistake of using #25 chain without precision turned spacers. We used spacers cut from sheet stock which got the dimensions "about right," to a degree which would have been acceptable for #35. "About right" wasn't enough, and we threw a lot of chain due to sprockets not quite mounted in the same plane. Finally, we used smaller sprockets than we needed to, which increased load felt by the chain, and reduced the slack needed to throw it. We never had a break or throw which looked consistent with overloading the chain, and it should theoretically never happen with the loads experienced in a typical FRC drivetrain, but I'm sure this intensified the other two problems.

I know of many success stories as well, and I'm pretty confident that we could have made it work with better tensioners, bigger sprockets, and more precise spacers. But the experience left a pretty bad taste in my team's mouth about the whole thing, and we're likely going to be using belts instead next season. More upfront design work required, but much lower maintenance. There are advantages to #25 chain; that's why a lot of very good teams use it. But proceed with caution.

Re: #25 Chain Drive Experience ???
 

3756 used #25 chain last year without issue. It does stretch quite a bit, meaning you have to either remove links or have some sort of other tensioning system to adjust every once in a while.

I personally love working with #25 chain... it feels almost like working with jewelry compared to #35. As mentioned by Joe though, it's quite a bit more picky in the way of sprocket alignment. We used 1/6" plastic spacers (from McMaster IIRC) to line them up, and they never popped except for when one of our sprockets came lose.

We use the #35 chain and sprockets that we have sitting around from the KoP for prototyping and practice bots, but I don't see us ever leaving #25 and 1/16" spacers for competition. (Edit: We had undersized aluminum spacers, leaving space for adjustments with the small plastic ones).

Here's a picture of our 2012 drive train. We had slots in the wheel brackets for tensioning. Worked well, but a pain in the rear to adjust in a 10 wheel drive -.-

Re: #25 Chain Drive Experience ???
 

Thanks for the feedback. Lots of (critical) gotcha's to watch out for.

Just in case I am missing something, what is the offsetting benefit of using #25 if there was so much stretching and retensioning required etc. Is it primarily weight savings (with sprocket weight savings) ?

Re: #25 Chain Drive Experience ???
 

While I can't recall exactly where I read it, I remember seeing somewhere that #35 chain is about 2.5 times the weight of #25, so the weight difference is significant. For the small amount of time it takes up front to line up the chains properly, and re-tension them a couple times throughout the season, the weight you save is definitely worth it. It also looks fantastic and is much nicer to work with, but those aren't exactly competitive advantages.

I highly recommend using multiple small plastic spacers if you join the #25 side. Makes lining up the sprockets a breeze.

Re: #25 Chain Drive Experience ???
 

Team 33 uses #25 chain almost exclusively on our robots. It is strong enough for pretty much any FRC application. Like many have said sprocket alignment is very important. Also, in our experience the chain doesn't actually stretch - the slackening is from the sprockets wearing in. Generally if you have a way to tention the chain about a half inch (such as a sliding bearing block) that is enough to take care of any chain stretching. Alternatively, we actually ran with loose chain in 2012 (chain was not pulled tight by a tentioner) and never threw a chain. I think a lot of the problems people have is because of misalignment: if you have confidence that you can align the sprockets well then I would give it a try.

Regards, Bryan

Re: #25 Chain Drive Experience ???
 

25 Chain is more than enough for drivetrain applications, assuming you have it aligned correctly.

To align sprockets, get a nice flat edge and span the distance between the sprockets. You should quickly see if they are aligned.

If you're direct driving the center wheel, use 25 chain for the front and back. Even a break won't put you out of business. If you are are not direct driving, use a double sprocket. Run one chain to the wheel in front of the transmission, and one behind.

The key to a successful drivetrain is NEVER reling on a single component, because it will break. From experience. (See Michigan State Champs 2011 where we sat motionless for 2 matches).

Re: #25 Chain Drive Experience ???
 

This past year, we used #25 chain to link the motors to the ball shooter wheel. We found that some of the sprockets that appeared to have irregular/non-standard tooth pitch. The large (28-32 tooth range) and small (10-16 tooth) sprockets were aligned so that they were co-planar. When rotated slowly, by hand, the chain can be seen to "climb" on top of one of the teeth of the large sprocket. This would always occur at the same spot on the sprocket regardless of which part of the chain was wrapped around it. We did not get significant wear on the sprockets or chain stretch. All the sprockets we had trouble with were stamped from sheet aluminum. On some of them, we noticed teeth that had "notches" in them, when new. It looked like the tooth pattern was "wrapped" around a circle that was slightly too large. We had to file the notch away to make the chain seat properly around that tooth.

I posted about this problem on a thread about #25 chain earlier this year. I seem to recall that some other teams ha no problems and some had similar problems and that it may be dependent on the supplier or even the batch of the sprockets.

Phil

Re: #25 Chain Drive Experience ???
 

Phil, we've seen the same thing. We generally just throw the ones like that away. They're so cheap it's not worth sending them back. On high torque low speed applications you can sometimes wait for them to break in, but on our shooter it was scary when they started jumping at 5k rpm.

Re: #25 Chain Drive Experience ???
 

There are several other threads where this has been discussed which you can read if you do a search but it basically boils down to several items already mentioned:
#25:
is strong enough for the drive train
is lighter
is more fickle about alignment

#35:
is heavier
more tolerant of misalignment
easier to work with.

My preference for drive is to use #35 and for mechanisms to use #25 in most cases. I don't like to have to worry about throwing a chain or even having to do real maintainance on the drivetrain which is what pushes me in this direction. Also I'm more comfortable with Al sprockets under that kind of wear at the #35 size. I know both work, but to me the trade-offs lean towards #35.

Re: #25 Chain Drive Experience ???
 

In the past 4 years I have been involved with the team, 610 has used 25 chain on our drivetrain 3 times. We only popped a chain off once. Alignment of the sprockets is crucial, but not really that hard if you design it in. Strength does not seem to be an issue, but larger sprockets lead to lower tension in the chain if you are concerned. It's hard to say, but the "stretching" one sees with 25 chain may actually be wear in the aluminum sprockets. In recent years, I have noticed the sprockets from AndyMark are made out of thinner sheet metal without any chamfer on the teeth. It looks like they are just cut on a waterjet. I'm sure this reduces their cost of manufacturing, but I liked the thicker ones with chamfers to guide the chain, and I suspect they would not wear as quickly since the base of the teeth was wider.
The real benefits to 25 chain are lighter weight and smaller size. Also, if you get the "dark soul" chain tool, making chains is really easy, with no more master links! It's actually much easier to work with than 35 chain.
Depending on the application, I would be hesitant to use 25 chain on arm joints and other heavily loaded mechanisms. Our flipper arms this year were powered by two 25 chains, and they broke a couple times. I think the shock of driving over the barrier or pulling the bridge down was more than it could handle over time.

Re: #25 Chain Drive Experience ???
 

With everyone saying its not the stretching but its the sprockets. Is there anyway to stop that? Would making steel sprickets be beneficial and still save weight?
We are thinking of switching but I gotta make sure before I use them. We will most likely use them on our prototype drive train this year.

Re: #25 Chain Drive Experience ???
 

During my time on 1503, we ran #35 chain in the drivetrain. While #25 is plenty strong enough, the biggest concern was sprocket allignment. Rather than spend hours machining spacers to 0.0005" tolerances, we felt our "quality" maching time could be better used for the parts that really needed it.

Personally, I'd rather spend the extra time and run #25 chain all around. The weight savings is huge.

-Nick

Re: #25 Chain Drive Experience ???
 

We generally use #25 for mechanisms and #35 for the drive-train.

According to AM #35 chain is .25lb/ft and #25 is .10lb/ft. In a drive train that used 16ft of chain (average for us I think) #25 series would save 2.4lbs vs #35.

This weight difference could be reduced by using smaller sprockets and no tensioner with #35 chain. We've used half-links to tension our #35 chain drives during initial assembly, never touched them after that, and never thrown a chain in the 3 years I've been coaching.

Re: #25 Chain Drive Experience ???
 

In my 12 years, I've run #25 chain on 9 robots (1 other was #35, 2 others were belts) and never threw a chain. You definitely don't need 0.0005" tolerances to get the alignment right. What you do need is careful design, and a little love at final assembly to ensure everything fits as designed.

I understand the "bullet-proof persona" that comes along with #35 chain, but I think any team is capable of using #25 if they want to. It just comes down to taking the time and effort in areas where you usually may move fast. Theres no need to machine spacers of +/- 0.001" of each other when you can buy shim stock and punch out spacers in whatever size you may need.

I know our final assembly of our drives with chains was carefully done over a couple days to ensure everything fit as intended. This is at the point where all of the pieces of the drive are DONE: machined, polished, cleaned, anodized. It's often tempting to rush and throw every piece together in an hour. I think our track record shows taking your time at this step is time well spent.


One reason we actually switched to belts was to make assembly a bit faster, which absolutely did decrease the time required at that step.

-Brando

Re: #25 Chain Drive Experience ???
 

Honestly, in our experience (a short run in a gearbox and a short run for a big arm), alignment was important but not absolutely critical or anything. I mean, for teams without a lathe that use the Kitbot and extruded parts, 25 might be a challenge, but if you have any reasonable manufacturing capability it's more than doable.

Re: #25 Chain Drive Experience ???
 

Generally chain "stretching" is every little join on every link wearing.
The reason you see more stretch on #25 is not because it is weaker but is because you have more links per inch to wear down.

Re: #25 Chain Drive Experience ???
 

It is also partially attributed to the lubrication slowly working its way out of each pin joint.

Re: #25 Chain Drive Experience ???
 

Tom

Did you order extras? I have been working with small teams so we have been ordering just enough + 1 spare so when both sprockets come in with notches in them, we are stuck. I will consider different sources in the future but the steel ones from Grainger get pretty heavy when the tooth count gets high. Does anyone have any suggestions for sources of better quality #25 sprockets other than AM?


Nick and Rob

It was great to see your most eleagant robot in the flesh in St. Louis and to be able to speak to some of your students. It was one of our favorites this year. I think your school is just a few km of where we used to live in TO. See you next time.



Phil

Re: #25 Chain Drive Experience ???
 

AM is the only person in the market that sells sprockets in #25 in aluminum. Maybe some other supplier might, WCP will in the distant future :p

But for now, you could send them back? We've called AM a few times for random misc. problems, they've been so kind to ship out replacements ASAP.

Instead of buying them you could router/laser/waterjet them from .118 or .125 plate and then chamfer them yourself? Do you have access to a CNC machine or do you have sponsors that own them?

-RC

Re: #25 Chain Drive Experience ???
 

In my experience, even #25 chain can be run fairly misaligned under some circumstances. Last year, we ran our practice bot with one sprocket on backwards. Their was not much load (it was an intake being powered), and the misalignment was fairly substantial, approximately 1/4" over about a 4" run. When we realized that it had accidentally been installed incorrectly, it had been running that way for almost a week with no problems.

I'm sure that high tension, high load drive chains are much more given to throwing with misalignment, but don't get scared away from a lighter solution. To add one more story to the others in this thread, we've run #25 drive chains for at least 4 years with absolutely no problems with misalignment. We did experience a bit of stretch, but our tensioners have solved that problem very handily.

Re: #25 Chain Drive Experience ???
 

#25 chain at 5k RPM in general sounds scary. We had to massage our sprocket sizes for our intake to ensure that we would not exceed the rated surface speed of #25 chain and that was substantially slower than a shooter wheel.

Re: #25 Chain Drive Experience ???
 

We've done it on a prototype. It was a little scary bit it worked.

Re: #25 Chain Drive Experience ???
 

In our shooter, our surface speed probably topped 4000 surface feet per minute. We geared up the output of a CIM through chain, which gave us an output RPM of about 7500. It never threw a chain, but it made a noise like the starship enterprise booting up.

For an even more crazy number, our belts (which were what actually touched the ball) had a speed of about 5890 surface feet per minute. That's almost 70 miles per hour. The saddest part: we could barely even make shots from the key.

Re: #25 Chain Drive Experience ???
 

That's got me wondering: what's the failure mode of #25 chain at these speeds? How is that surface ft/min rating established?

Re: #25 Chain Drive Experience ???
 

Agreed. As soon as we started talking about speeds of 4k+ RPM, we completely eliminated chain as an option.


Tristan- I'd also be very interested in that answer.

-Brando

Re: #25 Chain Drive Experience ???
 

My concern with exchanging the sprockets is that it would just be a waste of time. Since both sprockets had the same "notch" in them, this is indicative of the design or the CNC programming of the sprocket so any replacements would also likely have the same flaw.

Unfortunately, we do not have access to a CNC nor do we currently have sponsors who can make one available to us.

What alternative power transmission method is recommended at these high speeds? Belts? Gears?

Thanks.

Phil

Re: #25 Chain Drive Experience ???
 

Could you post a picture of what you're talking about? An error on two sprockets doesn't necessarily mean the whole production line is ruined - and I'm sure if you sent AndyMark a picture they would let you know if your replacement would have the same defect.

Re: #25 Chain Drive Experience ???
 

Unfortunately not. Once we saw how the notches affected how the chain seated on the sprockets, we filed the notches out so that we could get on with testing. We neglected to take photos so the evidence is gone now. Also, I am working with another team this year since we moved across town. Driving over 40-60 minutes one way was not fun.

I did some hunting around and found some aluminum sprockets with hubs made by Berg. These use set screw hubs and "pin hubs" so it may be best to broach a keyway in them.

www.wmberg.com/catalog/catpage.aspx?url=pdf/B05A107.pdf


I also found some glass reinforced nylon sprockets made by Torque Transmission.

torquetrans.com/roller-chain-sprockets/index.htm


I will give their distributors a call and see what their stock looks like.

Re: #25 Chain Drive Experience ???
 

Hi Rob

Where do you buy the thicker AL #25 sprockets ?

Re the Dark soul tool ( http://www.team221.com/viewproduct.php?id=70 ) I had no idea that it got rid of the masterlink. Thanks

Dave

Re: #25 Chain Drive Experience ???
 

AM used to sell thicker sprockets with a chamfer. Now they are thinner with no chamfer.

-RC

Re: #25 Chain Drive Experience ???
 

Unfortunately I don't have a source for aluminum sprockets other than Andymark. I was just pointing out the change in quality in recent years.

These look interesting. Please let us know if you get pricing and availability. We tried using a large nylon sprocket from Mcmaster carr on our intake this year, and had trouble with the chain not engaging properly. The pitch seemed to be off for some reason.

This makes a lot of sense. Team 359 uses bike chain which is 0.5" pitch, but much narrower than standard #40 chain. I'd be curious to hear from them how much stretch they see (if any). My understanding is that bike chain is way stronger than #25, but lighter than #35. Unless you could adapt bike sprockets, you would have to make your own. Other than that, it seems to be a great compromise between #25 and #35 chain.

Rob

Re: #25 Chain Drive Experience ???
 

Sorry to pull up this thread again, but has anyone found a reliable source for chamfered #25 aluminum sprockets? Does anyone know about these RobotShop guys?

Re: #25 Chain Drive Experience ???
 

I've never heard of them, but I'd suggest checking McMaster-Carr.

Re: #25 Chain Drive Experience ???
 

Unfortunately, McMaster has never sold aluminum sprockets. (They're strictly steel/stainless and nylon.)

Re: #25 Chain Drive Experience ???
 

Sorry about that, missed the aluminum part of your post. It looks like many of the #25 sprockets on AndyMark are aluminum. Are they not chamfered, or the wrong size, or something?

Re: #25 Chain Drive Experience ???
 

Yes, AM changed their #25s at some point. They're now thinner and no longer chamfered, and we're having systematic issues with CNC notch defects. There was a bunch of talk earlier this month about it, but it was never resolved into a different supplier. We're currently looking either at fixing the bolt pattern and bore on the less expensive RobotShop ones or crossing our fingers and trying to lathe a chamfer on AM's thinner ones. Wondering if anyone found a different solution.

Re: #25 Chain Drive Experience ???
 

I've never ordered sprockets from them but I ordered a couple robots kits from them for work. The kits were backordered but other than that arrived fine and worked quite well. Just don't try calling their phone support, it's terrible.

Re: #25 Chain Drive Experience ???
 

Does anyone happen to know, off-hand, what the change in material thickness on AM sprockets was? I'm looking for the thickness of a sprocket with chamfer versus one without a chamfer.

Re: #25 Chain Drive Experience ???
 

I believe the new sprockets are .125" thick. I know they are waterjet.
I'm not sure however how thick the prior ones were.

EDIT: Sorry, I was talking about plate sprockets. Should have been more careful.

Re: #25 Chain Drive Experience ???
 

Waterjet?

There's no way they're waterjet, unless you're talking about plate sprockets. It would make absolutely no sense to waterjet the tooth profile then turn them down to create the hub.

Re: #25 Chain Drive Experience ???
 

I could believe that the larger plate sprockets are waterjet. As far as I know, the smaller sprockets with a hub are still machined, and still have a chambfer.

Re: #25 Chain Drive Experience ???
 

Is something wrong with the hubbed sprockets? I'd only had/noticed people discussing issues with the plate versions. (Type A for AndyMark)


And thank you, Andrew. We'll probably get one from them, then.

Re: #25 Chain Drive Experience ???
 

Oops. My bad. Poor reading comprehension on my part. Didn't realize which was being discussed.