Chain Tension-er?

We are using #25 chain for a device on our robot and we are fairly new to chain and were wondering how we sould tension it as its at the tighest it can be yet there is still some slip from it drooping slightly does anyone have any ways of applying tension the chain?

Are you using a chain tensioning tool to assemble the chain?
If taking a link off seems like too much you may need a half link.
Edit: picture of tensioning tool.

For my team’s chassis we used rounded Delrin bolted onto the frame. I don’t think that this is the best method but it fit and it works. You can also have a spinning pice of Delrin or bearing that the cabin runs on.

You can add an idler sprocket somewhere along the chain’s length. Put the sprocket inside a slotted hole or use metal that has several holes to move it around, which will tension and detension the chain. IF your team can afford it, McMasterCarr sells spring-loaded tensioners here.

Great suggestions

If budget is an issue. These types of tensioners are used on many cars on the timing chain.
For Rebound Rumble we got one off a junk Toyota (free :smiley: ) and used it on our chain driven ball delivery system.
Works great.
Even new they are not a deal breaker.

Such as the OSK listed here.

Nice thing about the car ones, besides being durable, they are wider and you can offset your chain groove.

Good time to create a connection with an auto parts store in the area.


If the chain is long enough, an easy ghetto chain tensioner is to wrap a sturdy tie wrap between the two. I thought it was a dumb idea, but it does work.

My team had one of these things sitting around while we were chaining this year’s robot and we couldn’t get the right tension with just shortening links. We have no idea where it came from or if we have another somewhere, but we tossed it in one section and it works beautifully. We fully intend to use more of them to tension our chain if we can find where the darn thing came from.

Two things:
First, if you are transferring torque to the sprocket (i.e. it is not an idler sprocket), you really want to try to get over 120 degrees of wrap on the sprocket. It isn’t a hard and fast rule but it is pretty reliable. I’ve had a number of cases where I reconfigured routings to get over 120 degrees of wrap, chains that were jumpy and poppy and just creeping me out have settled down and I’ve never had to worry about them again. 120 degrees of wrap. It’s a big deal.

Second, it is almost always a mistake not to design chain tensioning into things from the start. You can sometimes get by without it (especially if you can have good wrap angles on all your torque transferring sprockets). Idlers are a nice option depending on your chain routing. I am a fan of moving one of the axles – even wheel axles which can be done successfully.

My suggestion is that when you use slots to provide your adjustment, do not depend soley on the clamp load of screws to keep your center distances from moving. If you have some slots in a bracket, then have another screw that helps take the load if the screws that are in that slot loosens up. I am doing a terrible job of explaining this. Here is a photo of the concept on a BMX bike chain.

Finally, chain tensioning by moving center distances is more easily done with dead axles where you can use eyebolts as your adjustment mechanism.

Joe J.

If you are REALLY tight on resources, one of the simplest tensioning techniques is to stick a big sprocket into the middle of the loose chain run - without actually attaching the sprocket to anything - it just floats in the middle of the chain run. The sprocket has to be big enough to take up all the slack, and is held in place by the chain run itself, with chain running above and below it holding it “securely” in place.

Don’t know if this makes sense, but it does work decently well. Surprisingly the sprocket won’t fall out unless directly disturbed…

This is a hack we used on 188 pretty effectively back in the early days. ::ouch::

If your device doesn’t require the entire chain to travel around a sprocket (for a linear section of a device that travels back and forth) we found this works very well.

lol thanks. i dont know how well this would work on a drive train but we can defiantly try it.

MCMASTER sells a dohickythat works like that. Only for #35 chain and bigger but it at least confirms the concept.

Dr. Joe J

Our team was in the same situation last year. We use 16’ of chain to drive our lifting mechanism to lift totes/bin. We spent 2 days trying to figure out how to tension the chain, and in the end decided we didn’t need one. Those 2 days would have been nice to have back and have some drive practice.
We went the entire season and never had a problem with our chain.

So that’s where what we had came from. Why on earth does that cost $70?

I saw that, yeah, $70 is crazy for a bit of plastic (or rubber or silicone or whatever). One thing to keep in mind is that while it may keep your chain from derailing it is not going to do anything for the backlash as you go from fwd to rev and vice versa. Not a huge deal on wheels (probably) but feedback loops hate backlash so… …keep that in mind (and do the right thing, put in a real chain tensioner :wink:

Dr. Joe J.

We found that flexible sprocket device too and I was wondering if something like that could be 3D printed out of some material that would give a similar effect. Anyone have thoughts about this?

Also from my reading it seems like tensioning addresses at least two separate factors. The first is making the chain the correct length for the application. This can also be solved with careful design and manufacturing. The second is compensating for chain stretch. Which of these sounds like the bigger factor for an application like a drive train?

I suspect if you could get it to print right with the proper spacing, ABS would have enough flex without being too squishy or too rigid. The trick is getting it right.

As far as spacing, the only actual problem is length, which chain stretch contributes to. The three options are 1. ignore it, 2. tension it, 3. have some way to move a sprocket around so you can move it back when chain stretch.

I would laser cut this thing before I tried to 3D print them. But even that seems a bit sketchy to me. As I recall (I have only held one in my hand once and it was years ago), the reason the device is a hoop and not a disk is that the hoop structure allows it to become an ellipse and thereby add some springiness to the system. As slack becomes available the ellipse gets more round and takes up that slack.

Bottom line, this thing flexes. I think a 3D printed version is doomed to destroy itself over time.

Dr. Joe J.

I highly recommend an idler pulley. My team has used a bolt with a piece of pvc around it. To attach the bolt, we tighten it with a lock nut through a slot on a piece of sheet metal. The one thing about this is that the nut has to be really tightened down. Otherwise it’s about as light and simple as you can get.

We’ve also used spring loaded tensioners. These had their advantages and disadvantages. The big advantage was never needing to worry that the chain was tensioned after the tensioner was attached. The disadvantages are of course cost, but also weight. Additionally, support like a wood block must be added to the bolts used to attach the spring tensioners if they cannot be mounted directly onto a frame element.

We have also used 3d printed pieces on a belt drive. They are a half moon shape sized to tension the belt without needing to be adjusted.

We’ve used this product from McMaster every year.

Expensive, but totally worth it.