pic: 114's new tensioner



Here she is. I killed the tab trying to upload it, dunno if it got through.

Anyway, it’s a three piece tensioner, bolt pulled. The two main bearing housings bolt together with #5-40 screws. The threaded shaft is held between the two. The whole setup runs through the 2x1 box extrusion that we love to use for our frame. It’s lighter than the previous version, and much simpler too.

Questions and comments welcome.

I don’t know if it qualifies for the tag “supersexy”:smiley: but its close.

With my teams second option for whatever the game may be being 6wd most likely, Im loving seeing all these tensioner setups and chain runs being posted.
I believe this design eliminates and toe-in or out due to the fact both bearing blocks are bolted together. I’ve started doing the same thing in my head i did with our swerve of piecing together parts i’ve seen on other similar drivetrains. One of these days i may actually cad it.

Did you mean 4-40 instead of 5-40? 5-40 is an awfully strange size.

I see a problemo!!! If you tighten it enough, the bolt will start pushing on your collar going through the rail. I’d recommend pulling the nut part of the tensioner out a bit so you can have more travel.

I really like this idea thanks for sharing it I may show the team it at sometime lol

It looks great. I would be concerned with the tension bolt loosening. Instead of using a bolt for tensioning, you cold use a threaded rod with a hex insert at the end for an allen wrench. Then by tapping the end plate on your 2x1 extrusion, you can put another nut on so it would be double nutted.

Also you could make the “halves” so they are not really halves, but one thicker than the other. Then you could just thread one of them and eliminate the round part. The hole for the tensioning bolt can go thru to the center area, since it only has to “miss” the axle.

I think it’s a neat design, I also think you can refine it quite a bit more to make it more simple or easier to make. This part of the process is great fun!

What are you concerns over constantly changing your robots wheel base? I’ve seen a few systems that work like this.

Hmm, this is in deed much better than the last design. For further refinement, you could turn the bolt around so it faces the opposite way, screwing into a nut that’s spot-welded to the frame or an immovable delrin block. Flatten the round shaft on the bolt at one point to give 2 or 4 flat surfaces for a wrench and I think it’s nearing perfection.

It’s still fantastic as-is though.

Team 971 used a tensioner like this last year, and that really wasn’t a concern for us. The amount that the wheelbase actually changes is insignificant when compared with the distance between wheel contact points.

Impressive, it looks very similar to the tensioner that 968 used last year. Another fine example of west coast teams sharing each other’s designs to the benefit of all. No wonder the quality of play has increased so dramatically!

I’m all about visuals, and understanding things by seeing them… but…
uh… what is this for?
I’m actually quite lost on this one it seems. :frowning:

Edit: Ok. Seeing this pic helped me see what it was going to be used for.
http://img50.imageshack.us/img50/1556/wheeltensionerandframeur8.jpg

There is only one issue I can think of right now. When you move the bolt so the head is sticking out of the frame more to increase(?)/decrease(?) tension as it may be, wont that bolt go out of profile if your frame is not short enough to account for that? (Edit: Wait… will the bolt head move, or is it just acting like a lead screw? <-- Answered below by Nuttyman. Thanks. I was imagining something a little different than how it actually works.)

It is a cool concept.
But, I would have rather used a turnbuckle style fastener between the centers of the pillow blocks rather than something on the outside if that would be possible while not interfering with the chain itself running (presumably) inside the box extrusion.

Also, a side question for teams who run chain inside box extrusion.
Have you ever had problems of your chassis getting damaged and thus the deformed shape interfering with the chain running inside?

It acts as a lead screw to slide the bearing block in the frame slot.

You beat me to the punch. lol Look at my edited question I popped in. I guess some issues are non-issues now. Thanks for the explanation.

I think this is where you’ll end up on the next iteration, Craig. The concept is sound, as I see it, and it’s pretty much where I ended up a few weeks ago – though I’m probably a few iterations farther down the road and I’m interested to see if we end up in the same place.

Also, the extant model has far more space for adjustment in the frame rail than the screw provides. You can narrow the opening to the length of your required adjustment – .25" for 25 chain and .375" for #35.

For what reason are you intending to press your bearings in to the outside of the bearing block? I think you could change that a bit and end up with bearing blocks that can be cut in one op. instead of two. :slight_smile:

We’re looking at implementing a cantilevered drive system like this, and am wondering if those bearing blocks are absolutely neccessary. We’d rather just bore the 2"x1" rail to accept a flanged bearing/bushing, and not have to machine a “complex” bearing block. Are teams finding that the 1/8" rail wall isn’t strong enough? Or is the support span on the axle too narrow for the applied torque? Or, are teams simply not following the KISS rule and making unneccessary machining for themselves?

If we have to go to a bearing block setup such as this, I do really like the tensioner outlined here. I agree that it can be made simplier, maybe out of just one piece. How does the cross rail mate up this to assembly, and does that connection (bolted or welded?) interfere with any of this?

Thanks,

Bengineer
Team 228

This is all making our practice of drilling two holes thru a piece of fiberglass I beam sound very easy…

To my knowledge, 195’s 2007 chassis was built as your describing – bearings pressed into 1x2" tube.

We use bearing blocks because I can mill a set and some extras in an hour or so on our mill and they’re easy to replace in case of some catastrophic failure. Our mill’s travel is only 20", so I can get accurately spaced bearing holes into a frame member in one operation and we’re very likely to screw that frame member up on some other way down the line. Bearing blocks minimize the time spent redoing work, I guess. :slight_smile:

I wish there were some better, more considerate reason for our process. But, with the time constraints we have, taking baby steps is preferred – even if they’re more complex – than putting all of our eggs into one very complex, important basket. Of course, I understand the definition of “complex” varies from team to team. We have awesome machining resources, but none of us are great machinists, so we work with what we have.

We used a similar system in the 07 season, and have never had any issues with the bolt backing out or loosening. Doing the other setup is actually more parts, and more machining needed.

I’ve been trying to work on a one op setup, but I’m not sure exactly how to do it yet. The reason for putting the bearings on the outside is to allow as much stability on the axle as possible, which still keeping the setup as small as possible. As for the adjustment size, you have to be a lot more precise with your chain length if you shorten the adjustment size. We prefer to keep as much precision out of something like that as possible, for when you need to do those hasty repairs in between matches. Instead of only 1 link of travel, we prefer to have at least 3 to 5, so it’s simple to swap out when we need to.

The next iteration should be 1 op, we’ll see how that goes.

Thanks for the feedback!

294’s post 2004 prototype and the 2006 base both used the team 60 inspired tensioning method you are talking about.

Each bearing block was simply a block of 3/4" Al (that was slightly thinner actually). All the necessary features fit on there (The bearing holes, the threaded hole for tensioning…) and it was much simpler to make; Just one piece per wheel. It wasn’t all that heavy either, a lot of material was able to be removed to lighten them.