pic: 114 6wheel tensioner
 

Re: pic: 114 6wheel tensioner
 

This is a fantastic chain tensioner system, hard to believe no one's replied to this in 6 months. On our prototype frame, our tensioner mounts are designed to be maintenance-free as well, but it's not nearly as elegant as this. Nice design!

Re: pic: 114 6wheel tensioner
 

Hmmm... So it is kind of the inverse of the older style of tensioning the "west coast drive" (like 968 last year)?

I like it.

Re: pic: 114 6wheel tensioner
 

This is pretty much exactly like what 968 did in 2006, I think.

Re: pic: 114 6wheel tensioner
 

Okay, some questions...

What size and thread was the bolt y'all used for tensioning? I'm presuming the attachment bar was tapped for that bolt. It looks pretty thin, so I'm curious how many threads you had engaged to keep tension in the chain.

Did you have any problems with it vibrating loose during a match?

Re: pic: 114 6wheel tensioner
 

We just used a 1/4 20 bolt. It held fine. The plate closest to the wheel was tapped, and 1/4inch thick. The other plate is not tapped. We only had to tighten the bolts once per competition: right before any final match. It's a wonderful setup. This variation is a bit heavy, due to two bearing blocks. I've since redesigned it to only need one frame rail, as well as only one bearing block.

This design, with two bearing blocks, yields a beastly solid frame, but at the cost of too much weight. The singe block design is much lighter, though less beefy.

Are you thinking of maybe using this design?

Re: pic: 114 6wheel tensioner
 

I've been working on something that incorporates a bolt for tensioning similarly to this -- the actual arrangement is quite different, but the theory is the same. Some folks on the team have expressed concern about the bolts backing themselves out, so I am just searching around for experiences with this type of system.

I've been working around a 3/8-16 bolt since it's going into plastic. Coarse, big threads are the order of the day for us.

Re: pic: 114 6wheel tensioner
 

We used this method on a few robots, the first I think was back in '97 or '98. The only drawback is when you run out of adjustment room, you have to remove a link in the chain. So the adjustment range needs to be a little greater than one link in length.

Re: pic: 114 6wheel tensioner
 

Are you doing this within one frame member like 968 in 2006, or 60 in various years; or are you doing it like 114?

If like 60, we used that tensioning setup with a #10 and it wouldn't vibrate loose that much. Usually 1-2 times a regional we'd check and the chain was slightly loose, we would it half a turn or so, and be good to go. We use the same concept on our with no problems (also ran it in 2007, had to tighten it about as much as in 2006).

So, short answer. No, it shouldn't loosen much and it should work just fine. Over the various years we've used this method, I've never seen it loosen so much over the course of one match to actual cause any problems.

Re: pic: 114 6wheel tensioner
 

When in doubt use a locking nut to prevent any movement. Loss of tension can be disasterous.

Re: pic: 114 6wheel tensioner
 

Yes -- this is being added to an existing design that has well-tensioned chain because of the sprocket's center-center distances. Still, adjustment is .375" for #25 chain; One and a half links.

It's going into a single bearing block in something evocative of the "west coast drive". My concern for the bolt size is because the bearing block is plastic and we'll need more contact area on the threads to keep loading in a reasonable place, so we have to increase bolt size or the number of threads engaged. It's easier to achieve the former.

I am hoping to get away with a nylon bolt, so I don't know how much use a locking nut will be for us in that case. When everything is assembled, there will be no access to anything on the inside -- including a locking nut -- so that gives me pause, as well.

We were considering a method of capturing the bolt head and preventing it from rotating, but it's a bit of challenge to devise such a system that allows enough flexibility in where the bolt head lies to make using this for tensioning practical.

Re: pic: 114 6wheel tensioner
 

McMaster sells bolts with a nylon patch on the tip-eliminating the need for a locknut.

However, I have no idea if they work/work well in plastic.

Re: pic: 114 6wheel tensioner
 

I don't think a nylon lock nut or bolt is even necessary. We used this system with no locking methods at all, and it worked wonderfully.

I look forward to seeing pictures on how you all implement this!