#25 Chain

[Sh1ine]

Hi Folks,

Typically we use belt for our drive train. This year with the bigger wheels we are decided that we wanted a stronger transfer method so we switched to #25 chain. We are running 8" AndyMark Pneumatic wheels, with a WCP Dual Speed Gearbox. Our low end is about 6 fps and the high is about 12 fps. We keep breaking chain. Is anyone else having problems with the large wheels breaking the chain? Some on the team want to switch to #35 chain, but that seems like overkill to me. I feel like we must be doing something wrong, not that the chain is too weak.

Thanks!

[billbo911]

Alignment, alignment, alignment.

#25 chain needs to be aligned properly.

NO HALF LINKS!!!!

That is how we are using it this year and so far, so good.

BTW, #35 will work and is not overkill.

[Munchskull]

Originally Posted by billbo911

Alignment, alignment, alignment.

#25 chain needs to be aligned properly.

NO HALF LINKS!!!!

That is how we are using it this year and so far, so good.

BTW, #35 will work and is not overkill.

What is wrong with half links? Are they extremely weak?

[JamesCH95]

As a team that has successfully implemented #25 chain in numerous situations, including both drive-trains and serious arm mechanisms, we switched to #35 this year for our drive after snapping #25 a few times.

A few things I've seen in our own robot:

Alignment is key. A chassis/drive pod/drive assembly must maintain that alignment under all game conditions. This includes thrashing around on a defense. A chain that looks well-aligned statically may not be aligned at all when dynamic loading is considered.

Related: if you're not using beveled sprockets, you're going to have a bad time.

Shock loading is brutal this year. With dramatically inconsistent contact with traction surfaces during defense crossing wheels will spin up, then catch, then spin up again. This dynamic behavior can potentially overload chain.

If you use #25 chain, make sure you're using #25 HD chain. Typical #25 chain is quite weak.

As mentioned we changed our drive-train to #35 this year. We are still using #25HD on our main shoulder joint though.

Originally Posted by Munchskull

What is wrong with half links? Are they extremely weak?

Extremely weak... maybe... weaker... yes.

[Joe Johnson]

Originally Posted by JamesCH95

As a team that has successfully implemented #25 chain in numerous situations, including both drive-trains and serious arm mechanisms, we switched to #35 this year for our drive after snapping #25 a few times.

<snip>

First, as someone who's admired Grasshopper Machines for 20+ years, I am going to tell you that you really need to give JamesCH95's experience strong weight.

Almost all my experience with successful #25 chain implementations on drive trains comes before anyone used conveyor belt for tire tread and certainly before pneumatic tires with sprockets that bolt on were only a few clicks away. It may very well be the case that with these new fangled grippy tire options, young'ins these days just have to go with #35 chain for their own safety.

Originally Posted by JamesCH95

<snip>

Related: if you're not using beveled sprockets, you're going to have a bad time.

<snip>

Amen brother JamesCH95, amen.

Dr. Joe J.

[2544HCRC]

I didn't see any reference between 25 and 25H in this thread. 25H is a far better solution without the weight of 35. It is still a bear to work with, but way better than standard 25. And yes, you have to run 25 tighter than you would think. 25 is very sensitive to alignment and tension. Somewhere I was told the "7 tooth minimum" rule. No idea if it is folklore or real but it works in general. Keep 7 teeth engaged at all times. This means no drive sprockets smaller than 14 teeth on a simple drive.

[BeardyMentor]

I build silly tiny electric cars and race them. I have run #25 chain for hundreds of hours with motors equivalent to 6+ CIMs to big (by FRC standards, 11") pneumatic tires. and it works just fine even under shock loads like getting put into the wall at 20mph. I even did some testing with 6.5hp brushless motors spinning a 20 tooth #25 sprocket and it worked fine for FRC time scales of less than a couple of hours of operation. With that said, I would swap over to #35 if at all possible. In my experience it is much more forgiving in fabrication tolerances and dealing with the unexpected situations like those that are common in FRC like getting repeatedly rammed, stalled motors, slight shifting of sprockets etc.

[Ether]

Originally Posted by 2544HCRC

I didn't see any reference between 25 and 25H in this thread.

...

Originally Posted by JamesCH95

If you use #25 chain, make sure you're using #25 HD chain. Typical #25 chain is quite weak.

As mentioned we changed our drive-train to #35 this year. We are still using #25HD on our main shoulder joint though.

[Jon Stratis]

Personally, I like to overbuild everything. I don't like things breaking, and the degree to which I overbuild is directly proportional to how critical it is for success. The drive train is probably the most critical part of the robot for success. I would never use less than #35 chain for a drive train. Then again, since we made the switch a couple of years ago I'll jump through hoops to avoid using chain at all on the drive train - direct drive all the way!

[cbale2000]

IMO, #25 chain is great for mechanisms but unless you know what you're doing it's a pain for drive systems. Some teams can make it work, but most underestimate the level of difficulty to get it right. Essentially #35 chain has the benefit of added tolerance for mistakes, so as others have rightly pointed out, the quick fix for #25 chain acting up, is to just use #35 chain.

That said, issues with chains breaking, skipping, and maintenance are the main reason we no longer use chains on our drive system. Geardrive ftw.

[galewind]

Thanks for this thread. It's very enlightening.

Does anyone have a reliable source for #25HD chain? It's a bit harder to find, from my cursory looks (the vendors we use don't sell it).

Thanks!

[mrnoble]

Originally Posted by galewind

Thanks for this thread. It's very enlightening.

Does anyone have a reliable source for #25HD chain? It's a bit harder to find, from my cursory looks (the vendors we use don't sell it).

Thanks!

http://www.wcproducts.net/roller-chain

[JamesCH95]

Originally Posted by cbale2000

IMO, #25 chain is great for mechanisms but unless you know what you're doing it's a pain for drive systems. Some teams can make it work, but most underestimate the level of difficulty to get it right. Essentially #35 chain has the benefit of added tolerance for mistakes, so as others have rightly pointed out, the quick fix for #25 chain acting up, is to just use #35 chain.

That said, issues with chains breaking, skipping, and maintenance are the main reason we no longer use chains on our drive system. Geardrive ftw.

I would argue that if you can make a drive unit rigid enough to not mis-align gears, and precisely enough to enable proper gear meshing, then you can make a drive that can easily handle no-maintenance chain or belts reliably.

And, yes, no-maintenance (aside from lubrication, which gears need too) chain drives exist.

Originally Posted by galewind

Thanks for this thread. It's very enlightening.

Does anyone have a reliable source for #25HD chain? It's a bit harder to find, from my cursory looks (the vendors we use don't sell it).

Thanks!

VexPro only sells #25HD as far as I can tell, by deduction in that they only sell #25 HD master links and state that only HD master links work with their chain. Comparing it side-by-side with other #25 chain sources makes it even more obvious.

I wish they'd state it on their website though...

Edit: boy, Dr. Joe sure knows how to make an engineer blush...

[D.gimon]

Originally Posted by billbo911

Alignment, alignment, alignment.

#25 chain needs to be aligned properly.

Agreed.

We used a #25 chain, six 8" pneumatic wheel, 22 tooth Vex sprocket drivetrain this year and had no major problems. We worked hard to make sure that all of the sprockets were aligned. We also used the Dark Soul chainbreak tool to assemble the chain in order to avoid using links and it worked well. There was some slack that showed up and one chain slipped off so we had to improvise a chain tensioner using large zip ties and encountered no further problems. We were quite pleased with the results.

Now I must also add that our robot was well under the weight limit (90 lbs) so I think that helped.

In the future, depending on the nature of the game and if we are close to the weight limit, I think I'd go with #35 just for peace of mind.

Dan

[Classified*]

#35 Chain is definitely not overkill! CIA has used chain drives in the past and #35 is the way to go, especially if you get in a pusing contest with a defending robot. Also, how big are your sprockets? Using small sprockets increases the stress on your chain. Simply using bigger sprockets lightens the load on your chain.