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

i am very curious to know, and would like to make one. please any details would be awesome, as well as pictures... please!

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

There are many different elements required for a 6 wheel drivetrain, so to get a better idea where you are coming from, could you describe the type of drivetrain you are used to?

Essentially, the basic concept behind a 6 wheel drive is that the middle wheels are lowered, so you are only driving on 4 wheels at a time, which will reduce scrubbing immensely while turning. If your robot is balanced well, the front and back wheels will lift off the ground while turning, and only your middle wheels will be in contact with the ground.

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

mainly, im thinking of getting out of anything im used to, for me it just doesnt seem to be working.

i want a fast and speedy drivetrain with the power of a tank. 25 seems to do that well.

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

Well what exactly are you used to?

4 wheel, wide drive? Ackerman?

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

4 wheel

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

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.

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

so how far would the middle wheels be lowered? 1/4 inch?

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

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.

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

1/8" is all you really need...

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

any pictures to help furthur my options or help me in any way would be most helpful and def accepted. i really thank you u all for helping me with this much info so far

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

would love some pics

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

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.

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

Well, the simplest way is the KOP frame. If using KOP wheels (you'll need 6 of them obviously). Put four at the ends like you normally would. There is a hole that is slightly lowered in the center of the frame that you should use for your middle wheel.

It is lowered to relieve the pressure from the corner wheels so you can turn easier.

The easiest way to run chain is with the center wheel having two sprockets and the ends having 1.

http://andyburchardt.com/robotics_re...0Drive%201.jpg

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

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.

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

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.)

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

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.)

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

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

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

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

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

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.

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

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

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

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.

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.

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

i would just like to ask, whats the pro's and con's of using 6 wheel drive, as against 4-wheel or treads(which are generally 2 wheel)?

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

6 wheel gives you the ability to turn on center. It also allows you to in general, turn better than 4WD robots (unless using omni's in some way).

When it comes to ramps and uneven surfaces, the middle wheel on a 6WD prevents the robot from bottoming out as well.

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

and im assuming the con factor is the extreme weight added on by all that chain?

also if using the 6 wheels on the same level configuration, wouldnt one have problems with traction, as well as weight if used omni wheels? if its a defensive game i.e. 06, wouldnt u get pushed around a lot?

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

Well, MOST 6WD drive configurations lower the center wheel at least 1/8".

I don't understand your question about being pushed.

There is significant weight added. However, the bonus to that is that it is also lowering your CG. Omni wheels weigh just as much as regular wheels in most cases. You lose no traction. In fact, if using a grippy tread, like the KOP wheels or IFI nitrile tread, you gain a little traction.

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

For two more wheels on our robot, it probably adds at most 3lbs. We only have 4 #25 chains on our drive train, which is probably only a pound once you add them all up. The only way someone can push you with 6WD is if they get in front of you and push you back against your motors, or if they get on a corner and push, but then all they do is turn you.

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

on the chain subject...i have seen a #25 chain break and it wasnt crappy chain either....IMO its worth it to spend a little more weight to get the #35 chain which you know will not break with the amount of force that is put on it....again thats just my personal opinion but 1126 used #25 from '03-'06 and then we had a severe failure in 06 that caused us to switch to #35

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

say a robot is to come and push against a corner, wouldnt you spin and not be able to push back, if u have omni wheels for front and back?

and for the 1/8th lowered, why would u only want 4 wheels on the floor at the same time? i wouldnt think that the weight added would be worth the extra 2 wheels if u dont use them. you lose traction for the wheels that arent on the ground, say someone bumps into u around that area, you would spin

im not bashing 6wd, im trying to find out pros and cons

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

Weight's never been an issue for us--neither of 1618's 6WDs have really broken 100 pounds. This year's robot weighed in around 78 pounds at Chesapeake, minus the forks we'd removed. That's all with #35 chain, and last year's robot was bolted together. A judicious application of #25 chain (or, if you're 125 this year, belts) and rivets could drive that down further.

Omniwheels don't have to weigh much either--compare the without-bearings weight of the 2007 kit wheel (0.75 pounds) and the AndyMark 6" plastic omniwheel (0.75 pounds).

I know there have been teams that have had defensive-oriented robots with omnis on the corners--488 last year comes to mind--but I'll yield to them since we've always run traction wheels in our 6WDs.

I'm still yielding on the omnis-on-corner discussion, but I'll bite on the other.

We actually use all six wheels on our 6WD, just not at the same time. Consider a robot that didn't have the front two wheels, with the other two left where they are. If you stop, the parts of the robot still doing 14 fps are going to want the robot to tip forward. Without those wheels, we're digging into the ground or rolling on some type of caster that affects how we turn (read: easily). The added weight is a non-zero amount--probably about a pound and a quarter or a pound and a half per side for us--but it's worth it in our determination.

As for traction, you're not really losing any. Granted, that particular wheel has zero traction with the floor if it's raised, but your four wheels in contact with the ground make up for it well enough to make up for it in most situations. Also consider that their front probably takes enough room to hit the middle wheel as well--unless they clip a corner and clip it well, you're still probably not turning.

And, since 6WD can enable easier turning, you can readjust quickly. :)

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

As with any good drive system that uses some form of drive like chain and sprocket/belt or whatever else, tension is key.

The fact that chain "stretches" was enough to make us consider using something else. Kevlar does not stretch, or at least, the stretch is minimal to the point that we dont need to adjust tension. This allowed for a very simple solution to tensioning, which was putting a piece of delrin, turned down to the proper diameter, placed over one of the standoffs already in place on the drivetrain. The results so far?? No skipping, slipping or sliding. I couldn't be happier with belts.

A LOT OF THOUGHT needs to be put into a drive system. You have to try and be adjustable for different situations, but you need to really commit to something from the start. I love how our drive train came out this year. If you have any more specific questions let me know.

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

6WD is heavier than 4WD, typically, but that doesn't mean that it needs to be heavy. This season, our drivetrain is 35 lbs. with electronics -- lighter than most 4WD systems. It's not as powerful as some, but that wasn't important to us.

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

A couple things I saw on this thread I want to comment on the distance the wheel should be spaced down is not a set distance it depends on what kind of wheels and traction material you are using. For instance wedge top tends to compress, so 1/8 may not be enough if you are using wedge top material in particular. Also the thoughts on 25 vs. 35 chain, this all depends on what kind of fabrication/machining facilities you have. I will now tell you why this matters. #25 chain requires more precise alignment then #35 because of the size difference. However #25 is much lighter and will save you weight to do other things with. #25 chain is plenty strong we used it in the drive last year for the first time and only broke it once and that was in a pushing match against 233 at a off season in Tampa and 233 broke there #25 chain as well. Just my thoughts on how to make an effective 6 wd base. I have been involved in two 6wd designs on 1251's 06 and 07 robots both won regional events these comments are things I learned on both those robots.

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

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.

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

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

How did it work out?

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

This year we used a six wheel dive based off the KOP frame and wheels. It works great an is still easy to drive even if one chain is lost. There are two chains on each side one each chain goes from the transmission to the center wheel and then one chain goes to the front and the other to the rear. This keeps the center wheel powered even if one chain fails. I've found that as long as the center wheel remains powered the robot can still be driven effectively.

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

The feeling you are getting is partially substantiated. The problem with that solution is the middle wheel has slightly larger diameter, but rotate at the same speed as the outer wheels, so they are bound to scrub a little because the middle wheels move slightly faster than your outer wheels.

6WD drivetrains are designed to rock back and forth a lot, and this should eliminate any and all issues you might have with this. If you are pushing the carpet into itself, you will just rock some more. Additionally, the change in diameter will only change the circumference by a slight amount, (~5-10%). I am sure any effects are completely negligible.

I should note that we did the exact same thing. We were having troubles turning at Portland (heavy bot, only 1/8" lowered, carpet), so we screwed on tread to our colsons at SVR, and we turn much better, although we rock back and forth a lot now.

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

Also if at all possible try to direct drive the center wheels. We did that for the first time this year and it makes things so much simpler. Then you only need 4 chains so the only extra weight over a 4 wheel drive design is the weight of 2 wheels and sprockets which is probably 1.5 lbs. We have always gone with the center wheel lowered 1/8" with both kit wheels and colsons and have never had a problem.

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

There are a lot of teams I know of that uses 4x4 aluminum box tubing for their chassis. Back in 2007, I talked to Karthik and he directed me to Taylor. They were gracious enough to share close pictures of their chassis. Personally, I love 6wd and in my designs I use an 1/8th inch drop. Below are few pictures that may help you.

http://www.chiefdelphi.com/media/photos/27523 ... that's 1114's 2007 chassis
http://www.chiefdelphi.com/media/photos/29996 ... that's 1345's 2008 chassis
http://www.chiefdelphi.com/media/photos/26373 ... that's 1345's 2007 chassis

1114 makes their own plates and puts the transmission inside the box tubing. It's very neat. If you have any questions, I would suggest getting in touch with Karthik and I am sure he will be more than happy to share their designs. Also, if I can be any help, you are more than welcome to send me a pm. Good luck.

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

This year we did six wheel drive with a unique twist. We originally tried four wheel drive, but wanted a tighter turning radius.

We didn't like the tippy drive with the center wheel lowered so we used omni wheels on the front and back with all wheels at the same height.

On the kitbot frame we drove the middle and back wheels with the toughbox gearboxes. Then we slaved the front wheels to the middle ones (so the middle wheels had two sprockets - one on each side.)

Picture:
6WD Pic


We were happy with the results and seemed to have quite a bit of power.

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

Our team has attempted six wheel drive systems for the last two years. We did extensive prototyping work in both 2007 and 2008 to develop six wheel drive systems. And guess what... we ran into the SAME problems in both 2007 and 2008, too much traction and difficulty turning.

We solved these problems the same way both years; removing two of the traction wheels are replacing them with omnis. We noticed HUGE increases in performance when we replaced the wheels. Our robots were much more nimble with only four traction wheels.

At the Portland regional this year it occured to me that powering the omni's was a waste of time. I mean, how much traction are you gonna get out of an omni wheel anyways? So we removed the chains from our omni wheels. Do you know what happened? Nothing. Except we lost about a pound of weight.

So here is my challenge to teams using omnis this year: take off the chains and see what happens. You may be surprised to find that there will be no change in preformance.

What I've learned amounts to this:

-4 WD* Is the best configuration for a game with no obsticles. 4 WD is more controlable than 2 WD and is significantly simpler than 6 WD.

-6 WD Is only neccessary when there are obsticles to climb over. Fewer wheels and you'll increase the risk of bottoming-out.

*With the wheels oriented in a square NOT a rectangle.

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

Hello guys!

I'm 17 years old, and robotics is a big interest of mine.

Recently, I built a 6 wheels drivetrain chassie with a 1/8" center wheels drop.

the chassie looks like this one (the only defferance is that i'm using 2 motors in each side with one gearbox, two motors that goes to the same gearbox):


my problem is that i'm not a programmer, so i can't drive it. i wish someone can provide me a good code, which is Appropriate for 2 joystick drive so i can try it (one joystick for the right wheels and the other for the lefts).
please provide me the best code that you can, because i know nothing about programming and i can't amend the code.

in addition, i'll be very thankful if some one can provide me with a geartooth sensors code for this drivetrain (2 geartooth sensors, one for each gear).

thank you alot! :)

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

I've found that adding two wheels is as simple as it sounds: add two wheels and two more lengths of chain (though this year we didn't even need to add more chains, just make them longer). 6wd is not more complicated than 4wd, it's just a little more work. We've used 6wd with 1/8" center drop for the last two years without any problem, and we've found it to be very maneuverable. Our chassis this year could be made with hand tools, and only took a few days to assemble.

http://www.chiefdelphi.com/media/photos/30068
http://www.chiefdelphi.com/media/photos/26813