#25 Chain Drive Experience ???

[philso]

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

[Tom Line]

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.

[Peter Matteson]

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.

[Rob Stehlik]

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.

[akoscielski3]

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.

[Nick Lawrence]

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

[JamesCH95]

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.

[Brandon Holley]

Originally Posted by Nick Lawrence

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.

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

[Chris is me]

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.

[IndySam]

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.

[Aren_Hill]

Originally Posted by IndySam

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.

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

[de_]

Originally Posted by Rob Stehlik

.....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 "dark soul" chain tool, making chains is really easy, with no more master links! ....

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

[R.C.]

Originally Posted by de_

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

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

-RC

[Rob Stehlik]

Where do you buy the thicker AL #25 sprockets ?

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.

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.

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.

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.

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

[Siri]

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?