Re: Chains for 6 wheel drive
 

just a quick question, I see you bolted into 80/20 for your wheels. did you have any problems with the two outside wheels coming loose during competition?

Re: Chains for 6 wheel drive
 

No. This was not a significant problem.

We did check chain tension in the pit. If loose, we utilized the 80/20 grooves to tighten the chains (loosening the bearing block bolts; shifting the blocks to tension the chain; tightening the bearing block bolts). This was probably a once-per-competition event.

We used economy nuts in the 80/20. We have generally found that these do not tend to slip if they are tight. In fact, they tend to bite into the 80/20's aluminum and need to be tapped with a hammer to move after loosening the bolt.

Re: Chains for 6 wheel drive
 

A small caveat to Clem's post I would just like to point out is that Lunacy drivetrains tended to be much more forgiving in terms of chain tension, and things coming loose. This was due to the slickness of the floor/wheel interface. Wheels can only exert so much force on the ground, and in the case of the Lunacy game, it was much smaller than usual.

Just wanted to point that out, the sliding tensioner blocks may have worked great for Lunacy, but for games with more aggressive surfaces (ie: carpet), they may not work as well. Thats not to say it cannot be done, it just will require some extra effort.

-Brando

Re: Chains for 6 wheel drive
 

I really, really like the simplicity of using extrusion and sliding blocks to tension chain like that. Have any teams successfully implemented this in a high traction drivetrain? Machining bearing blocks out of solid and making a reliable mechanism to hold them in place and adjust them as needed is difficult, and this looks too simple.

Re: Chains for 6 wheel drive
 

I wouldn't say it is difficult at all. Any team with a manual mill could EASILY pull it off.

Re: Chains for 6 wheel drive
 

I'm a strong advocate for having at least one set of wheels direct drive off the gearbox.

I've just seen too many robots (including some of our early ones) limping around the field with one or both chains trailing behind them. Yes, you can build a gearbox/wheel chain link that will give you gear adjustment and will be reliable, but direct drive reduces the risk that you won't get it right.

We used the extended drive shafts and 14:1 gear ratio on an AM toughbox to drive these VEXPro wheels on our 8wd robot last year. You can see the gear link up in the attached thread. By turning the nylon rollers down to size we were able to get pretty perfect chain tension fairly easily.

http://www.chiefdelphi.com/forums/sh...highlight=1346

Once you've got the direct drive set up, then I'd only ever connect two wheels with one loop of chain. It just makes tensioning easier, ensures excellent sprocket/chain connections (lots of teeth in contact) and means that even if you lose one chain, you don't lose your entire drive system.

Remember... you might spend six weeks building a robot that will only get to play eight matches. You don't want to have one of those matches spent limping around the field with a busted drive train!

Jason

Re: Chains for 6 wheel drive
 

In 2003 and 2004 when I was on team 100 we used 80/20 and a similar method of sliding pillow blocks for dead axles to tension the chain.

It didn't work very well at all for us because we were not actually pulling/pushing the blocks with something. We were just physically by hand pulling the wheel until the chain was tight and then bolting it down. It didn't take long for the blocks to slip in the extrusion.

If you were to setup a screw that either pushed or pulled the wheel to the outside of the robot and kept everything in tension to resist sliding it would work much more effectively.

Re: Chains for 6 wheel drive
 

Team 1444 has done 6WD a few different ways. First was to drive the center wheels directly from the transmission (both one and two speeds) and then have one chain to the rear and one to the front; similar to what is posted above. I believe one year, you also drove the rear wheels directly then used a single chain to connect the front two wheels (one each side). This worked fine, but it was move difficult to manage and tensions, but really I so no difference in performance between the two methods.

We have also used gears to connect all six wheels. We drove the rear wheels directly, then used gears all the way up the sides to connect to the front wheels. The advantage of this is that it is easy to get another stage of gear reduction and you get instant engagement; you don't have to wait for the chain to tighten up. It is also much quieter. However, there were a TON of gears and a lot of precise machining.

For simplicity's sake, I would go with the double chain drive described above. As mentioned before, it is always good to drive one set of wheels directly. The middle is usually the best choice is you are using proper tank/skid steering with the center wheel lowered.

Re: Chains for 6 wheel drive
 

Maybe it's just alien to me then. The task of designing a block that retains two bearings, slides easily in tube, has a mechanism for holding itself in place, and reacts against some other feature of the drive for adjustment (be it a cam, screw, or otherwise) has always seemed somewhat daunting. Probably because I've never tried it...

I should probably bow out of the rest of this discussion.