Weird Chain tensioner.

[artdutra04]

Originally Posted by joeweber

You can eliminate the need for a chain tensioner if you preassemble the sprockets and chain than measure the distance to center, than build the distance into your frame. As long as you only have two sprockets in each chain set it’s a piece of cake. This will also save some weight.

I've found that this only works for chain runs with a center-to-center (CTC) distance of less than about six or so inches for 25-pitch chain. If using 25-pitch roller chain with CTC distances of greater than about six inches, chain stretch becomes large enough that it can cause performance issues without a chain tensioner.

[M.Wong]

In the past couple of years, we have built in quite a bit of tolerance in they way we mount our transmissions and motors. We will usually have slotted holes in our chassis for mounting, allowing us to adjust for small amounts of chain stretch.

We have not determined whether or not this affects performance or autonomous.

[joeweber]

Originally Posted by artdutra04

I've found that this only works for chain runs with a center-to-center (CTC) distance of less than about six or so inches for 25-pitch chain. If using 25-pitch roller chain with CTC distances of greater than about six inches, chain stretch becomes large enough that it can cause performance issues without a chain tensioner.

That sounds good for a six wheel drive, three wheels with a motor and gears between each wheel.


" O o O o O "

[Ryan Dognaux]

This can also be done if you have an extra sprocket laying around that is larger than the two sprockets that your chain is running on. We've called it the floating sprocket - it's a real quick way to tension your chain if you're in a pinch and it works surprisingly well.

[Enigma's puzzle]

but usually if you plan for it and buy some "add in" masterlinks which is a half a link you can usually be close enough to make it without tensioners, and you can determine if you need them as you build the chain http://www.mcmaster.com/#chain-links/=7540yq

[Triple B]

For a drive base with skid steer & direct drive for your center wheels I would agree with "joeweber" that there is no need for chain tensioners. When the chain stretches to a length you deem too loose, then change the chains out. The tensioner may give you the illusion that your chains are in good condition when in fact the chains are still stretching you just dont know how much. Dont get me wrong, tensioners are nice but in my experience they are not always required. But I also like #25 (1/4") chain for everything.
mike d

[artdutra04]

Originally Posted by Triple B

For a drive base with skid steer & direct drive for your center wheels I would agree with "joeweber" that there is no need for chain tensioners. When the chain stretches to a length you deem too loose, then change the chains out. The tensioner may give you the illusion that your chains are in good condition when in fact the chains are still stretching you just dont know how much. Dont get me wrong, tensioners are nice but in my experience they are not always required. But I also like #25 (1/4") chain for everything.
mike d

At about $3/ft, throwing away stretched roller chain is a more expensive endeavor than installing a $0.50 chain tensioner.

Waste not, want not.

[Chris is me]

Originally Posted by artdutra04

At about $3/ft, throwing away stretched roller chain is a more expensive endeavor than installing a $0.50 chain tensioner.

Waste not, want not.

Would it be cheaper over time to break the chain and pull out a link, if this happened more than once?

[PAR_WIG1350]

Originally Posted by Chris is me

Would it be cheaper over time to break the chain and pull out a link, if this happened more than once?

you would have to remove at least 2 at a time and add in a half link, depending on the type of half link, you might have to remove three. Also, the chain might not stretch an entire link before it needs to be fixed. thus, you use a tensioner.
Of course, if there was considerable stretching, removing a section of chain would make sense.

[artdutra04]

Originally Posted by Chris is me

Would it be cheaper over time to break the chain and pull out a link, if this happened more than once?

Unless the chain stretched a full two links, it's time consuming to take apart and would require the use of a half-link. A well designed chain/belt tensioner integrated into the rest of the system adds on a few ounces of weight, and can be tensioned in seconds.

[Triple B]

I was not saying to waste chain, but with or without a tensioner, the chain stretches close to the same amount. I would rather change the chain when it is determined to have stretched a given amount rather than to keep tensioning the chain until it fails. In my past experience, I believe having a chain fail during a match is priceless and would much rather spend the $3 per foot on chain. Each year we have used the same chains for two regionals, Atlanta, several off season season events, and quite a bit of testing with zero problems. This has been the case over the last 4 seasons and our 2008, 2009, and this years robot all have the original chains from build season.
mike d

[sdcantrell56]

Originally Posted by Triple B

I was not saying to waste chain, but with or without a tensioner, the chain stretches close to the same amount. I would rather change the chain when it is determined to have stretched a given amount rather than to keep tensioning the chain until it fails. In my past experience, I believe having a chain fail during a match is priceless and would much rather spend the $3 per foot on chain. Each year we have used the same chains for two regionals, Atlanta, several off season season events, and quite a bit of testing with zero problems. This has been the case over the last 4 seasons and our 2008, 2009, and this years robot all have the original chains from build season.
mike d

I completely agree with you and think this is true, so long as the chassis is extremely rigid. If the chassis has any amount of flex the looser chains could easily pop off of the sprockets. I know 233 uses box extrusion for the chassis which must make for an incredibly rigid setup not allowing for any misalignment.

[Aren Siekmeier]

The last two years our team has used short segments of some Delrin rod we have lying around as tensioners. We mount the flat face of a cylindrical segment with a bolt off center, making somewhat of a cam, and then the round face is against the chain. The cam part allows us to just loosen the bolt, rotate the Delrin to retension the chain, and tighten it back up. Depending on the fastening method, the tensioner can rotate slightly when tight, which just means more frequent maintenance, but I think a little Loctite fixes this. This allows for an inch or so of tensioning and is fairly robust and lasts a while if done properly.

Attached is a screenshot of a rough CAD model of it in SolidWorks. The chain runs under the cylindrical Delrin rod, which is mounted horizontally to the aluminum angle which is then mounted to a frame rail or other structural element. You could even mount the Delrin straight onto the frame somewhere if it works out.

[sircedric4]

Originally Posted by compwiztobe

The last two years our team has used short segments of some Delrin rod we have lying around as tensioners. We mount the flat face of a cylindrical segment with a bolt off center, making somewhat of a cam, and then the round face is against the chain. The cam part allows us to just loosen the bolt, rotate the Delrin to retension the chain, and tighten it back up. Depending on the fastening method, the tensioner can rotate slightly when tight, which just means more frequent maintenance, but I think a little Loctite fixes this. This allows for an inch or so of tensioning and is fairly robust and lasts a while if done properly.

Attached is a screenshot of a rough CAD model of it in SolidWorks. The chain runs under the cylindrical Delrin rod, which is mounted horizontally to the aluminum angle which is then mounted to a frame rail or other structural element. You could even mount the Delrin straight onto the frame somewhere if it works out.

We have used this exact same setup ourselves for the two years we've been doing 2992. Also, those two years are the only years that we've not had a chain issue at all. Some sort of tensioner has been a lesson learned for us and something we plan to carry into the future.

As for the original post's floating tensioner, we used two very similar tensioners with great success on our super chain driven 2009 bot. They were made out of white nylon. Since we used them on the vertical positioned chains we didn't even have to move them or maintain them as gravity did that job for us. Here's a photo.

[Aren Siekmeier]

K.I.S.S. !!!