Re: Chain Tensioning
 

Same experience. Floating sprockets were one of the better/less painful tensioning methods 2220 used back when we used chain. I think we used them in one of the worst possible cases on our swerve drive (horizontal instead of vertical, lots of slack), but they still didn't give us any problems.

That being said, I vastly prefer trying to get as close to c-c as possible with minimal tensioning (on both chain and belt). Even if you still need a bit of tension, going as close to c-c (adjusted or exact) as you can means you can get away with a less beefy tensioning mechanism (in most cases).

Re: Chain Tensioning
 

If a floating idler sprocket is falling out of a chain run, the chain run is undertensioned. That's fixable just by moving the idler sprocket.

It's actually really important that tensioner sprockets "float". It is actually pretty hard to locate a single static position for a sprocket to engage both the top and bottom of a chain run, and this spot will change over time. In use, a "floating" sprocket may oscillate to maintain chain contact, but as long as the sprocket has reasonable contact with both sides of the chain it will stay roughly in the same place.

Rigidly mounting a "floating" tensioner sprocket is a very bad idea for this reason, plus it defeats the purpose of an idler sprocket tensioner - a simple solution to tensioning that can be adjusted later.

It's important when participating in a technical discussion to make your posts based on experience, or at the very least explain the logic of why you are making a recommendation. It's a mistake I've made before (probably still do occasionally, to be honest) and in the worst case it results in other teams making costly design decisions based on what is really just your conjecture. This is especially a big deal in communities of "smart" people who are usually correct on intuition alone - it's easy to become complacent and not give your ideas the scrutiny you should. So please, be clear with your rationale and tell people when you aren't speaking from experience.

Disclaimer: I have not used floating idler sprockets specifically on an FRC competition robot before, only on other projects using roller chain. YMMV.

Re: Chain Tensioning
 

Yeah, those sprockets never came out. And it makes sense that they should float. But I'm an EE so don't take this opinion as gospel.

Geez, 99 billion is a little dramatic - that drive had one, and only one, major problem. The turning motors were not geared properly plus they were window motors, my bad on both counts. We just didn't have the resources, time or money that year to re-design. Rick's drive was darn clever in many ways (for example the alignment block for the spur gears).

Have any CDers experienced significant chain "stretch" during a season? It is really bushing wear I reckon, the links do not actually stretch - I think. Is some chain better than others? Is it something you typically take into account? Is it a reason to use a tensioning device? Does 25 chain "stretch" more or less than 35 chain?

Re: Chain Tensioning
 

Not entirely sure what you mean by bushing wear, but in 2012 team 2220 had some major issues with our chain stretching in the finals at the Lake Superior regional-- which lead to us throwing a chain. That was why we added (hacked together, badly) tensioners for our next tournament. Come to think of it, it might not have been the chain itself stretching, but certainly sometime between ship and the end of Lake Superior the drive train wore in enough that our relatively tight chain was visibly slacking. We certainly blamed it on the chain at the time, but I'm not sure what else could have worn-- the bearings? The sprockets?

Regardless, a tensioner "fixed" the problem for North Star and MSHSL.

Re: Chain Tensioning
 

I have read that bushing-less chains "stretch" less than chains with bushings. The "stretch" comes from bushings or holes in the links wallowing out. It is particularly bad news if one uses aluminum sprockets since a worn chain puts more pressure (than normal) on the teeth under load.

For your team, it sounds like a tensioner was the solution. On the other hand we ran belts this year and broke quite a few (mostly due to under-sized pulleys). Those belts that did not break did not seem stretched leading me to believe the chain (in last years similar drive train) did stretch a little. Interesting problem...

Re: Chain Tensioning
 

Okay, that makes sense. Thank you for explaining that. I would hazard a guess that that was what happened.

Re: Chain Tensioning
 

The lovejoy tensioner that I linked to previously is made exactly for this. It rides with the chain and maintains tension. It's basically a captive idler on the end of an adjustable arm. They worked great for us at the 3 events we went to and assuming we can use them again and don't have to radically redesign the drivetrain for any reason, we will be. I'll try to get a video created the next time we are running the robot. It might be helpful for some teams. Fair warning, they are somewhat heavy being steel but the weight is down low and it really wasn't too bad. We didn't have any weight issues this year.