Chain Tensioners
 

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.

Re: Chain Tensioners
 

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.

Re: Chain Tensioners
 

This is #25 chain connecting two 14 tooth sprockets.

Re: Chain Tensioners
 

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.

Re: Chain Tensioners
 

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.

Re: Chain Tensioners
 

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

Re: Chain Tensioners
 

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:

Re: Chain Tensioners
 

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

Re: Chain Tensioners
 

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.

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

Re: Chain Tensioners
 

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.

Re: Chain Tensioners
 

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.

Re: Chain Tensioners
 

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]

Re: Chain Tensioners
 

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.

Re: Chain Tensioners
 

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)

Re: Chain Tensioners
 

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.

Re: Chain Tensioners
 

OO oo pick me Possibly Mechanum? We still have to try running it on the floor over a period of time with the tensioners to see how they do, which we will on Wednesday. We didn't really consider the chain sliding sideways, didn't have much of a problem when we had it propped up on the table. Oh well, we'll see.:D

Re: Chain Tensioners
 

I wish. :D Maybe next year...

Re: Chain Tensioners
 

We use elastomer tension rings from McMaster-Carr (p/n: 5896K1). They work great and are simple to install (just put it between the chain). See attached image...

Re: Chain Tensioners
 

Those tensioning rings are slick. Too bad they cost so much! At that price, the special polymer must be made from unobtanium.

Re: Chain Tensioners
 

We made a tensioner for our 05' bot. We just used a skateboard wheel on a piece of metal which was attatched to the frame and a spring keeping the tension. We just used scrap parts from our school so it was cheap and pretty easy to make. I'll try to get a picture up soon.

Re: Chain Tensioners
 

we are just using bolts to tension our chain but we want to use something on top of the bolts...

Re: Chain Tensioners
 

Be careful, metal on metal contact is not a good thing. Ideally you'd use idlers, but if you can't at least put a piece of PVC around the bolt.

Re: Chain Tensioners
 

i dunno if thats allowed... its not fair you can generate electricity from friction...

and we cant use them because of clearance issues.
weve had success in th past with no active tensioners. we have slots in our wheel bearing pillows. and we just slide them to the perfect tension. then crank on the bolts.

Re: Chain Tensioners
 

If our design permits, we either slide or place shims under the motor/gearbox assembly. This year, the initial tension worked out perfectly with no shims or half links or anything. How unsual is that!

Re: Chain Tensioners
 

I know what type of tensioner you are talking about. Google "Roll-On Tensioner". It's this rubber sprocket that tensions and dampens vibrations. We have neve used it, but ive heard that its good suff.