Chain Tensioners

[sanddrag]

I need to tension chains and cannot use the method of sliding one sprocket. The sprockets are fixed. I need to add an additional adjustable roller or something. The tensioning roller itself cannot be a sprocket though due to space and time constraints. The tensioner can only be supported on one side. Automatic (spring loaded) would be nice but not absolutely necessary. The chain is running between two sprockets only. Due to space constraints, I need to push/pull it apart to tension. To room to push/pull together. All parts must be fabricated or purchased locally due to time constraints.

Tonight, I tried a spring loaded pivoting rocker arm type setup and while it worked for the chain moving in one direction, it failed miserably for the chain moving in the other direction. If I had this pivoting arm such that it was not spring loaded but rather adjusted then held in place by friction, would that work? I'd really like an "automatic" spring loaded tensioner if possible, but I'll settle for anything that does the job well enough.

I remember seeing something on this site that was like a plastic sprocket but just the outside ring and it was very flexible and you put it between two strands of chain and it pushes them apart. However, now, I can't find it. I know I said parts must be purchased locally, but if this is an easy and effective solution, we might order them if we know where to get them.

So, basically, I'm desperate for ideas. Pictures are worth 1000 words.

Thanks so much.

[Travis Covington]

I remember seeing those rings you are talking about, and recall them only being available in #35 pitch and higher.

I'll take a look and see if I can find it.

[sanddrag]

This is #25 chain connecting two 14 tooth sprockets.

[Jizvonius]

You can try a floating tensioner depending on the diameter of the sprockets and the center distance (if it's too far, the tensioner will just make the chain touch for 14 tooth sprockets). This should work the same in both directions. as for not using sprockets for the rollers, you could use plastic sliders (preferably something like UHMW polyethylene or acetal)

How exactly to implement it would be dependent heavily on the dimensions of your design. but to get the basic idea here is a picture.



You could have a bottom slider with rails/bolts and a top one with through holes. Then you just need to tighten using nuts above the top slider.

[RogerR]

i'm using the pulley tensioners that came off of the big CIMs, since we aren't using them for anything else. the parts you are talking about are called 'roller chain tensioning rings', and can be found on mcmaster-carr using those keywords, but are only available for #35 pitch and up, as travis said.

[Lisa Perez]

We've used cylindrical nylon (about 1" in diameter) across the chain for OCCRA before, and it worked pretty well.

[artdutra04]

Originally Posted by sanddrag

I need to tension chains and cannot use the method of sliding one sprocket. The sprockets are fixed. I need to add an additional adjustable roller or something. The tensioning roller itself cannot be a sprocket though due to space and time constraints. The tensioner can only be supported on one side. Automatic (spring loaded) would be nice but not absolutely necessary. The chain is running between two sprockets only. Due to space constraints, I need to push/pull it apart to tension. To room to push/pull together. All parts must be fabricated or purchased locally due to time constraints.

... [shortened to take up less room]

So, basically, I'm desperate for ideas. Pictures are worth 1000 words.

Thanks so much.

Why not use something really simple, like a piece of HDPE or delrin rod with an off-center hole in it? My team (228) has used this successfully for the past two years, and it works great. Plus, it is: 1. Easy to manufacture. 2. Can be cantilevered. 3. Simple! Here are some diagrams/pictures of it in use on our 2005 robot:

[lukevanoort]

Grab some idler sprockets from McMaster (page 959) some U-bolts (many McMaster pages) and some springs (also many McMaster pages). Then, put the idler on the u-bolt, then mount the U-bolt so it goes through a plate of sheet metal, finally put a nut and washer on the end of the u-bolt and squeeze a compression spring between them and the sheet metal. A bad ASCII art diagram follows.



|| || bolt tops and nuts/washer
{} {} springs
[][][][][] sheet metal
\\{}// bottom of bolt and idler top
. {} bottom of idler

[s_forbes]

We had to do the same thing. We took the cheap and simple approach. We put a nylon washer on both sides of a nylon spacer and slipped it all over a bolt. The bolt then just bolted through a hole in our frame. We are using two of these nylon spacer contraptions on each of our loose chains. It's really sturdy, and gives our robot a nice growling sound when we fire it up at full speed.

. . [] .. []
{]-[]---[]----
{]-[]---[]----
. . [] .. []

[Dick Linn]

One year, we used wheels off of an old skateboard. We put it on a wood lathe (or was it the drillpress?) and cut a groove to fit the chain.

[Mentor Dave]

For our robot, we used 2 different sized hole saws - the larger diameter circle for the 2 outside pieces, and a smaller diameter circle goes in the middle to make the "groove." We bolt them directly to the frame. They don't have to turn, the chain will just wear against the wood.

We did consider cutting a slot in our frame so that the tensioners could be adjusted, but we deemed it unnecessary.

[Rohan_DHS]

we had some 'C' channel from the kitbot that we weren't using, and we basically cut it, made a groove through it like that (look below), made a slit so that the bolt can slide (not necessarry, i guess, could just use a wing nut, and remove when want to loosen chain), put a bearing on it (represented by the B in the diagram), which pushes up against the chain (labelled C) and tightened the bolt....presto! if you want more info, feel free to pm me

|C|
|B|
|=|
|=|

[edit]
realized that making the pic better just made it worse
[/edit]

[Jeff K.]

I saw another thread on here about using that Pulley Tensioner off the big cim motor. I modified a part of the support structure, the L Bracket to be able to mount that onto it and it works pretty well. We also used the spring that came with it to tension it. Our only concern is that pulley being round/grinded down by the chain. I'll post some pictures of it after our next meeting.

[lukevanoort]

Originally Posted by Stonefan5271138

I saw another thread on here about using that Pulley Tensioner off the big cim motor. I modified a part of the support structure, the L Bracket to be able to mount that onto it and it works pretty well. We also used the spring that came with it to tension it. Our only concern is that pulley being round/grinded down by the chain. I'll post some pictures of it after our next meeting.

Yeah, I thought about that when designing our tensioners, but eventually decided against it. Unlike idlers, it doesn't supply much resistances to the chain sliding sideways as well as a personal distaste for working with high powered springs. Eventually I had to ditch the design because we needed four tensioners. (Can anybody guess what we're doing? Hint: not omni) shortly therafter came the "block of HDPE" method... threw that one out due to bad experiances last year and an irritating mentor. Then came springloaded U-bolts which ended up mounted statically (although still adjustable) due to a lack of springs and length of the U-bolts. (Originally I planned to use the nice aluminum jobbies from McMaster, but they we're to wide, had to improvise)

[JakeM]

If a floating tensioner will work, or to test and see if one will, take some heavy duty zip ties and tie wrap the chain tight, to a reasonable level. Remember the purple and orange powdercoated watercut robot from team 781 2 years ago? These simple tensioners worked perfectly, never getting caught up, and if they broke, they were easy to fix. Once we did get the heavy ties though, there was no breakage.