pic: Kitbot Chain Tensioner 2

[Donut]

loading photo ...

[patrickbosch]

Could you tell me if these are store-bought or custom made? I'm running around in my head looking for new tensioner designs, but this one is perfect.

[EricH]

Looks like a store-bought pulley with the wheel pulled and replaced with a small sprocket.

On another note, is that a cooling rack being used as a base below the chain?

[Lil' Lavery]

Originally Posted by patrickbosch

Could you tell me if these are store-bought or custom made? I'm running around in my head looking for new tensioner designs, but this one is perfect.

It actually looks like the one of the fittings from the end of a pneumatic piston with a sprocket added to the middle.

[Simon Strauss]

What size chain is that?

Simon Strauss
1155

[DonRotolo]

When adjusting the tension, how do you prevent the sprocket from rotating? I am assuming you just hold it straight, but wonder if you have some ingenious mechanism that I can't see...

Very FIRST-like: Simple but effective, with commonly available items.

Don

[Doug G]

We tried an approach like that in 2006, but yours is very elegant. In 2007 we gave up with it and used a super simple solution... A chuck of UHMW PolyEthylene Rod with a hole drilled in it offcenter. Rotate it into the chain and whala... Tension!! Rotate it the other way and you can remove chain off the wheel. Very simple and worked well. True there is a bit more frictional loss - but in 7 years of competing, we never had a simpler, more reliable solution. .Here's a pic..

[Richard McClellan]

Originally Posted by Doug G

We tried an approach like that in 2006, but yours is very elegant. In 2007 we gave up with it and used a super simple solution... A chuck of UHMW PolyEthylene Rod with a hole drilled in it offcenter. Rotate it into the chain and whala... Tension!! Rotate it the other way and you can remove chain off the wheel. Very simple and worked well. True there is a bit more frictional loss - but in 7 years of competing, we never had a simpler, more reliable solution. .Here's a pic..

Just out of curiosity, where did you get those gears for the encoder setup you have? And how is the lower gear on the 1/2" Banebots shaft attached? Is it a set screw? Did it come with that 1/2" bore or did you have to enlarge it?

[Doug G]

Originally Posted by richardmcc2

Just out of curiosity, where did you get those gears for the encoder setup you have? And how is the lower gear on the 1/2" Banebots shaft attached? Is it a set screw? Did it come with that 1/2" bore or did you have to enlarge it?

Those are 36 tooth, nylon, spur gears that we ordered from McMaster-Carr (pg 1012). The come stock with a 1/4" bore, which is great for the encoders, but had to bore them out to 1/2" for the banebots and add a 1/8" keyway using a broach.

[patrickbosch]

Originally Posted by Doug G

We tried an approach like that in 2006, but yours is very elegant. In 2007 we gave up with it and used a super simple solution... A chuck of UHMW PolyEthylene Rod with a hole drilled in it offcenter. Rotate it into the chain and whala... Tension!! Rotate it the other way and you can remove chain off the wheel. Very simple and worked well. True there is a bit more frictional loss - but in 7 years of competing, we never had a simpler, more reliable solution. .Here's a pic..

Ha, we had this idea as well, except it was cammed delrin for a tensioner. It appears as if it worked very well, did you have any problems keeping the tensioner from slipping?

[Doug G]

Originally Posted by patrickbosch

Ha, we had this idea as well, except it was cammed delrin for a tensioner. It appears as if it worked very well, did you have any problems keeping the tensioner from slipping?

They rarely slipped. We thought we'd have to use special lock washers to keep it from slipping but never did they seemed to hold just fine. Truth be told that we always had them fully engaged which means the normal force from the chain on the tensioner is inline with the bolt, thus reducing the torque on the tensioner.

I really like using the UHMW PE. If you have never used the stuff, it feels like greasy PE.

[Gboehm]

Much better than my teams solution that I dare not say, cause the engineers would have a coronary...

[JesseK]

Originally Posted by patrickbosch

Ha, we had this idea as well, except it was cammed delrin for a tensioner.

I thought about having a delrin cam for a tensioner, but you'd have to screw it in pretty tight to keep it from rotating over time due to the force of the chain. 1885's '08 bot will have similar tensioners to the OP's, but instead of a pully it will be a delrin block based upon what we've watched at 2 offseason events.

I like these styles of tensioners because you can directly weld the chain tensioner mounts to the frame and still have a zero-maintenance tensioning system that's very lightweight.

[Donut]

Ah, sorry for late responses to these questions! I haven't logged in to CD in a few months now since I graduated and am getting used to the college experience.

These are all store bought parts for the tensioner, with the exception of that metal plate which is of course from the KOP. It's simply a nylon sprocket (#25 for our chain) inside of a clevis rod end, though you might even be able to do it with the ends of the pneumatic pistons as mentioned. These ended up costing around $17 per tensioner.

Below the chain is our cart, just a nice metal cage like some metal shelving in stores.

Come to think of it I don't remember how we stopped these from rotating, but I know it wasn't really anything special, I believe they're just held on by the screw going to them.