6wd - chain path revisited

[Andrew Y.]

i too would choose the last one. I have designed this one for the past 3 years and just continue to improve pond it. Though im running outa things to improve knock on wood*

[JHSmentor]

Originally Posted by JHSmentor

I am a mentor for a rookie team - hence, I am a rookie as well.

We have been researching 6wd systems and am curious what the pro's and con's are for the chain paths that could be used. I've included some very rough drawings (please don't pick on me too much over these!) to illustrate what we have been discussing.

I have my own ideas of some pro's and con's for these designs but would like some unbiased feedback so I will keep those to myself for now.

things to consider are drag created by the tensioners (if any), chain stretch even with the tensioners, dropping a chain, sprocket changes, wheel changes, stuff like that.

we will most likely be using as much of the kit parts as possible and filling in any gaps with similar or identical equipment - unless there are other cheap alternatives presented here.


thanks for the help!!

PS. the blue circles are the tensioners (still trying to figure these out), red are the sprockets, and the light blue are wheels - probably a mix of Omni's and kit wheels.

i updated the image to correctly draw the chainpath for the first image.

[BenjyPoore]

I like the second method best. This way if you break a chain or two you are in no way out of commission. I would use #35 chain for the motor-center wheel link, then #25 for the other 2 chains. This saves weight while still having some dependable #35 chain on there.

[JagWire]

My team has used the three-chain design for two years now, to great success. Though we have never used the kitbot transmissions.

I can't recall the exact shaft size we used for our axles, but I do remember that, two years ago, by the time we were half way through the qualifying rounds, the bolts we used were toast. We upgraded to some grade 8 bolts of the same size and haven't had a problem since. Though, getting those bent axles out of our wheels was a bit of a challenge I must admit. You can see a picture of the design we used two years ago here. I couldn't find much of a shot of the drive train from last year.

Other than the bent axles, the only trouble we ever had was getting those poof-balls stuck in the chains. We actually cut one in half during a match once, that was pretty cool... well, until it finally popped one of the chains off anyways. *Hopefully* we won't have a problem with that this year though...

[B.Johnston]

One more possibility would be to omit the tensioners at all.

Use a live center axle

If you use sprockets with an even tooth count and space them an even multiple of the chain pitch apart in a single drive/driven configuration you would be able to keep it really simple.

If the chain stretches enough to need tensioning throw it out.

It's really not worth losing the chance to go to Atlana for a couple of bucks worth of streched chain.

You also don't need the extra hardware needed for tensioning to complicate things as well.

(in the dark, on carpet ... with a ref asking you if you can continue. been there ... unfortunately done that... GTR finals 05)

[JHSmentor]

Originally Posted by 1680Bruce

One more possibility would be to omit the tensioners at all.

Use a live center axle

If you use sprockets with an even tooth count and space them an even multiple of the chain pitch apart in a single drive/driven configuration you would be able to keep it really simple.

If the chain stretches enough to need tensioning throw it out.

It's really not worth losing the chance to go to Atlana for a couple of bucks worth of streched chain.

You also don't need the extra hardware needed for tensioning to complicate things as well.

(in the dark, on carpet ... with a ref asking you if you can continue. been there ... unfortunately done that... GTR finals 05)

Unfortunately, we built a 2wd robot for an earlier competition and the chains stretched enough during the game that they tended to jump off. Using #25 chain just seems to require it if you have any distance to cover with it. Anyone else concure or disagree? all inputs are welcome. thx.

[s_forbes]

I would recomend the last setup (your third picture). That is the same as the drivetrain we had last year and we had zero problems.

Our first year we tensioned our chain by moving the wheel axles, and it didn't work well at all. Chain tensioners are not as much of a hassle as they are made out to be, and if they are done right they work very well. Here's a picture of some of our tensioners from last year.

What kind of transmissions are you using?

[NOV8R]

Here's a YouTube video of 1583's 6wd. http://www.youtube.com/watch?v=px-QCB9UeCsa It uses a single drive chain. We ran a similar design last year with no problems.

[NOV8R]

Here's a working youtube video link. http://www.youtube.com/watch?v=px-QCB9UeCs

[artdutra04]

Originally Posted by 1680Bruce

One more possibility would be to omit the tensioners at all.

Use a live center axle

If you use sprockets with an even tooth count and space them an even multiple of the chain pitch apart in a single drive/driven configuration you would be able to keep it really simple.

If the chain stretches enough to need tensioning throw it out.

It's really not worth losing the chance to go to Atlana for a couple of bucks worth of streched chain.

You also don't need the extra hardware needed for tensioning to complicate things as well.

(in the dark, on carpet ... with a ref asking you if you can continue. been there ... unfortunately done that... GTR finals 05)

If your team attends multiple competitions, it's a lot cheaper and more robust to just use a chain tensioner than to constantly keep replacing roller chain because it stretched.

Personally, I love robot drive trains that once they are designed, built, and assembled, you can more or less forget about them. (As opposed to constantly tweaking them between matches.) Nothing is better than going to a competition, getting through inspection Thursday morning, and relaxing in the pits between matches, because nothing broke or needs to be replaced.

[Jimmy Nichols]

Originally Posted by Teched3

We drive each wheel of a six wheel drive robot with an individual chain for each wheel. Hence, if a chain (or two) breaks or comes off, you still can drive and control your robot.

That is what we did last year as well. One thown chain does not take out the entire drive on one side of your bot.

[shock190]

Team 190 used the bottom design with no failures through two regionals, championships, and a good half dozen offseasons and a few dozen demos with no failures or chains dropped. For tensioners we simply had rollers of varying sizes we could swap on and off instead of an adjusting mechanism.

[EricH]

For the last 2-3 years, 330 has used the middle design. We don't use tensioners very much; last year the potentiometer mount served as a tensioner on the gearbox-to-center chain. We used #35 and figured out exactly where to place the wheels to eliminate tensioners. The big advantage is that a single thrown chain can't do a whole lot to you, unless it's the gearbox-to-center one, and even then you still have one wheel. We've only had one problem, and that was when a thrown/broken chain jammed between sprockets at the same time that we got stuck on an inner tube at the end of a match. It was fixed within one timeout.