how does one go about making a 6 wheel config drivetrain?

[CuriousGeorge]

4 wheel

[RyanN]

We had 4 wheel up to 2004 when we got tired of the robots tripping breakers and dancing around. Since then we've been using 6WD with the lowered center wheel. There are many pictures on our website: http://www.teamfusion364.org/Photos%20main%20page.htm)

Look at the build season photos, primarily week 1 and 2 for our drive train.

[danshaffer]

kitbot would be a good place to start, just chain your wheels together on each side (you'll probably drive the middle wheels and run chain from there to both the front and the back)
if you're feeling ambitious, you could replace the kitbot angles with 1/8th wall 2x1 or 3x1 aluminum box beam... I can post some pics of our drivetrains if you want them.

[CuriousGeorge]

Originally Posted by danshaffer

kitbot would be a good place to start, just chain your wheels together on each side (you'll probably drive the middle wheels and run chain from there to both the front and the back)
if you're feeling ambitious, you could replace the kitbot angles with 1/8th wall 2x1 or 3x1 aluminum box beam... I can post some pics of our drivetrains if you want them.

would love some pics

[EricH]

I found some pictures of 330's 6WD drop-center drive that somewhat show the chain routing.
http://www.chiefdelphi.com/media/photos/23376
http://www.chiefdelphi.com/media/photos/27675
http://www.chiefdelphi.com/media/photos/30206

Their chain run goes like this: Trannies to center wheel and rear wheel. Center wheel has another chain, which runs to the front wheel.

Just a note, the drive's various iterations have won 3 regional wins, 2 regional finalists, 1 world championship, and 2 divisional wins, with one regional left for the team to play in 2008, just on 330.

[EricVicenti]

Many teams choose to use #35 chain, but in my experience, it is way more bulky and heavy than necessary. Team 8 uses #25 chain. Keep in mind that tensioning is very important. The two ways of tensioning are to pull the wheels back, or to push the chain down, either with an idler sprocket, or some other material that wont wear out, such as HDPE.

Also, most teams don't directly drive any wheels with 6wd, which isn't a bad choice, but in terms of simplicity, we choose to drive the center wheels, and to have 2 chains run to the front and back. This year, we originally designed our drivetrain to use AM super shifters. When we found ourselves nearly overweight, we decided to make our own gearboxes from the toughboxes and the supershifters, so we ended up with non shifting gearboxes, 8:1 ratio (fairly high, higher than either the toughboxes or the supershifters), the size of toughboxes with the mounting pattern of supershifters.

[EricH]

Originally Posted by EricVicenti

Many teams choose to use #35 chain, but in my experience, it is way more bulky and heavy than necessary. Team 8 uses #25 chain.

Some teams won't touch #25 in the drive with the length of the overpass. They say it's too weak. It isn't, but if not done right, it can be. (The last time 330 used #25 on a robot was the second stage of their shooter wheel drive in 2006 going to the wheel. It was the first time since 2001, when contact was minimal and #25 was used in the drive. Later, we had a lot of problems with drive chains jumping while using 2001 as a practice bot.)

[EricVicenti]

Originally Posted by EricH

Some teams won't touch #25 in the drive with the length of the overpass. They say it's too weak. It isn't, but if not done right, it can be. (The last time 330 used #25 on a robot was the second stage of their shooter wheel drive in 2006 going to the wheel. It was the first time since 2001, when contact was minimal and #25 was used in the drive. Later, we had a lot of problems with drive chains jumping while using 2001 as a practice bot.)

Agreed, in 2007 we didn't do it right, and chain was snapping all the time. I am trying to remember what exactly went wrong, but our tensioning system was terribly designed, if at all. I dont think we had a plan for tensioning at all untill we were mostly built. Alignment might have also been an issue. (IE, if the sprockets were not close enough to coplanar, the chain would pop off.)

[kramarczyk]

I surprised that nobody has mentioned that 6WD can be done without wheel drop.

488 accomplishes this by using omni wheels on the corners. This style is shown in Madison's preso on FIRST Drivetrains... http://www.chiefdelphi.com/media/papers/2037

A variation of this I've seen on a few bots (45-2007) uses high traction wheels in the center and middle and lower traction wheels on the remaining corners. I'm pretty sure they used no wheel drop in this config. http://www.chiefdelphi.com/media/photos/28857

[Mr. Lim]

Here's a link for FIRST Robotics Canada's Robot Design Gallery. There is a section dedicated to drivetrains, many of which are 6-wheel.

http://www.firstroboticscanada.org/site/node/71

[kaszeta]

Originally Posted by kramarczyk

I surprised that nobody has mentioned that 6WD can be done without wheel drop.

Team 95 has used variants on this team for several year (two primary drive wheels coupled with driven omniwheels to avoid scrub) for several years now, this year in 6WD mode mentioned here.

[Brandon Holley]

A few clarifications:

-Center wheel drop isn't *necessarily necessary (See any of 25's drivetrains from the '03 and on)
-#25 chain can be just as effective as #35 chain

On the 2nd note there, if your team feels like taking a little risk go for the #25 chain, and make sure you do it right. Tension obviously is key. I have used #25 on my '04 drivetrain (where we did all reduction through chain and sprocket to pair the CIM with the drill and then finally drive the wheels, I believe it was 11 or 12 chains per side) I did it in '05 and I did it in '07...I HAVE NEVER SEEN A #25 CHAIN BREAK so I may be slightly biased, but honestly do not let the age old "#25 is too weak" stop you from trying it.

This year however, we used kevlar reinforced timing belts with aluminum pulleys. Around 1/6 of the weight of a comparable chain and sprocket setup, with very little noise and a very sleak design. I love them, and I see no reason to stop using them. See here: http://www.chiefdelphi.com/media/photos/30256

[RyanN]

Team Fusion has used #25 chain for many years now, and have only suffered once. This was last year, during the Bayou Regional when we used some Chinese chain that wasn't worth the weight it took on our robot and cost us the regional. We are now using Diamond chain, and are very happy with it. We have never had a chain break before in the 4 year's I've been on the team. Tensioning is the key. You cannot have slack with #25 chain in your drive train, as a whiplash can cause it to snap. In 2007 and before, we went with plastic sprockets for idlers, but this caused some trouble last year when we snapped the axle that the idler was running on. Now we're using nylon blocks and some hardened steel for tensioners (We put these on in Houston last year, and made something very similar this year). We have been very happy with this method. We use nylon block, but some certain type from McMaster Carr that has some lubrication fused into the nylon. I don't remember what it was called, but it works very well.

This year however, we used kevlar reinforced timing belts with aluminum pulleys. Around 1/6 of the weight of a comparable chain and sprocket setup, with very little noise and a very sleak design. I love them, and I see no reason to stop using them. See here: http://www.chiefdelphi.com/media/photos/30256

How are the belts working this year? We used belts in 2003, and I know it slips real bad, but the belts are 6 years old now and the idler is stretched to the max.

[Andy Baker]

Originally Posted by kramarczyk

I surprised that nobody has mentioned that 6WD can be done without wheel drop.

488 accomplishes this by using omni wheels on the corners. This style is shown in Madison's preso on FIRST Drivetrains... http://www.chiefdelphi.com/media/papers/2037

A variation of this I've seen on a few bots (45-2007) uses high traction wheels in the center and middle and lower traction wheels on the remaining corners. I'm pretty sure they used no wheel drop in this config. http://www.chiefdelphi.com/media/photos/28857

Yep... this year, team 45 is also using a 6wd without a dropped wheel in the center. All 6 axles are on the same plane, and all 6 wheels are 2008 Kit Wheels. The middle two wheels have been lathed down a bit and then a traction wheel tread has been riveted on. This makes the middle wheel about 3/16"-1/4" larger in diameter, compared to the outer wheels.

(edit...

Oh... by the way... team 45's 6wd uses only 3 different custom fabricated parts this year (not including bumper mounts). All of these parts can be made with a band saw and drill press. Stop by the pit in Atlanta and the kids will give you a tour.

... close edit)

Andy B.

[AndyB]

Originally Posted by Andy Baker

Yep... this year, team 45 is also using a 6wd without a dropped wheel in the center. All 6 axles are on the same plane, and all 6 wheels are 2008 Kit Wheels. The middle two wheels have been lathed down a bit and then a traction wheel tread has been riveted on. This makes the middle wheel about 3/16"-1/4" larger in diameter, compared to the outer wheels.

(edit...

Oh... by the way... team 45's 6wd uses only 3 different custom fabricated parts this year (not including bumper mounts). All of these parts can be made with a band saw and drill press. Stop by the pit in Atlanta and the kids will give you a tour.

... close edit)


Andy B.

So you just added tread right over the flat gum surface? Interesting... Too simple to be true it seems.

How did it work out?