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I am guessing by the looks this will be 2WD right?

Also, will your actual frame material be 80/20? This would definitely be a good base to use that with.

How thick plate do you plan to use for the bearing mounts for the front and rear wheels?

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Well... it doesn't necessarily have to be 2WD. The front and back wheels could just be on dead axels. I thought of a chassis and drive train that work like that, as well.

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Dead Axles? Never heard of that before...

If it is going to be a two wheel drive, may I suggest you use omni wheels on the corner wheels. This will improve your maneuverability greatly and prevent that skip the robot has everytime you turn.

It's looking pretty good. When do you think you will be having more of it done?

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That's cool DB, i was thinking about what it would be like if we turned the center wheel drive we had upside down. And what center wheels are those, they don't look like what we have?

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I believe that they are actually "poor man's" omnis (regular KOP wheels covered with pool hose so they can slide sideways easily)... Although I was hoping to get away from using them :D

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Bearings are in the wheel and sprockets are mounted directly to the wheel. The shaft doesn't spin. Dead and live axels have their advantages. If you do dead axels right, you can just remove to bolts holding it in place and the shaft can just move out of the way, making wheel replacement very easy.

What 1519 has done in the past is cut vacuum tube and zip-tie it to the corner wheels. They still get a bit of forward traction, but it greatly reduces the side scrub.

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But aren't they cheaper and don't they turn easier than omis??? But then again, we can always use something with more quality.

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Hi, I was wondering for a 2wd with six wheels can you lower the two centre wheels as you do with six wheel drives and is this anymore effective than omni wheels (or improvised ones).

Tim

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You can lower the center wheels on any 6WD. Now, if those are not the driving wheels, you may as well do a 4WD setup, but that's beside the point. It's pretty effective, but both methods (6WD "drop" style and 6WD coplanar, which has the omni wheels at the corners) have their fans. You'll want to experiment to find out which is better.

I'd also suggest powering more than two wheels.

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Although the normal KOP chassis is setup this way, I would avoid using the current configuration. A corner hit on the chassis can easily warp the frame out of alignment. Adding crossbars (making an X in the middle of the frame) or using round tubing instead of square tubing linking the left and right sides will greatly strengthen your frame. Of course, you will have an upper frame and bumpers to help out, but with a little effort, this could save you a lot of time at competition.

We have been using a square outer rail and middle round tubing for the past 4 years, and we've never had a frame issue. It was well abused at IRI and it only came back home with some small dents.

Round tubing is structurally stronger than squared tubing, and you cannot torque it very much without breaking a weld.

Before everyone says that the KOP frame is very tough, I want to say that this is my personal opinion and I do not want to discourage the use of the KOP frame. I personally like custom frames with round tubing. Auto manufactures use it for a reason, and so do many teams. I would love to hear some input on this as well.

For the wheel setup... If you drop the center wheel about 1/8th of an inch, you shouldn't need omni wheels on the outer corners. We've never had issues turning. Actually this year it turned too much. As for the dead axles... I assume you mean that the axles don't spin, but you have a sprocket bolted to the wheel that spin on the axle. If that is so, we did exactly that this year and didn't have any issues... actually, we have done this for the past 4 years. Our base design has stayed mostly the same with improvements each year. This year we identified a problem with using roll pins, and having them shear, so we're probably going to use larger ones next year or come up with a better way to attach the wheel to the shaft. We're also looking into stronger chain. We were pushing the limits of the #25 chain.

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Maybe not on all 4 corners though. Some teams have had problems in the past (us, for example) with controlling our robot by having a six wheel drive with 4 omni's. 2 omni's would probably be ideal, either on the front or in opposite corners. I'd also suggest powering at least the rear part of your drive, throw a sprocket and chain on that bad boy and you'd be good to go.

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This guy brings up some good points. One other thing to keep in mind is if it is a flat game or not. Omni's on both ends weren't terribly freindly for climbing ramps (06, 07). Also if only the middle wheels are powered, it is really easy to get the robot stuck if the front or rear gets propped up a little. Many center only powered robots experienced this phenomenom this year with the bumps created by the inner wall supports (08).
As the drove over the bump it lifted the inside drive wheel off the ground and the machine then swerved directly into the wall. From the stands it looked like poor driving. In reality it was just a little vehicle dynamics issue.

I have another thread going on 6WD dynamics. There is a good link to a paper that explains making your robot turn. My recommendation would be power to at least 4 wheels or have your powered wheels at 1 end of the chassis. This brings a whole new set of dynamics issues though (whip oversteer).

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Thanks to everyone for their comments.
Somehow the description didn't get posted when i uploaded the picture. What you see weighs 19 lbs. I haven't decided what gearboxes to use, but i have AM toughboxes or DeWalts in mind. The frame is 1x1x3/16 square tube, and will be welded.

Yes, Only the 2 center wheels are powered.

I was not planning on using 80-20 because it would make it heavier than i want this design to be.

The angle aluminum that supports the axles is 3/16 inch thick.

InfernoX14 explained dead axles.

Do you mean done in CAD, or built?
I will probably continue CAD of this design and similar ones until 2009. I don't know when i'll be 'done'.


To answer the comments about 6wd vs 2wd:
This drive base design was meant to be simple and light. Part of meeting this goal meant not powering the corner wheels.
For 3 out of the past 4 years, 1519 has used a 2wd drive, powering the center wheels only.

We have had good success with this design. The only drawback of this drive system is, like IKE points out, it cant climb ramps.

I like 6wd, but this design is meant to be the simple, light, stick-with-what-we-know design.


They are custom 6 inch aluminum wheels with roughtop or similar tread material.

They are 'poor mans omnis'. I'd like to get away from using them too, as are heavy.

Poor mans omnis are a lot cheaper than regular omni wheels, and they slide laterally very well, but not better than omnis.

Ryan, thanks for your advice about torquing the frame. Where would you recommend putting the round tube?

Comments are welcome
DB

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I edited out a lot of your post, but I would like to challenge you that if you are spending the time to do an upfront design, figure out how to power at least 4 of those wheels. There are some extremely simple and cheap ways out there and then you will drive better and be able to climb ramps (or bumps).

We have excluded teams in the past (06, and 07) as picks for having only the center 2 wheels driven from our elimination selection list. If you need some pictures of how to get 2 more to drive, let me know and I will send them your way.

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Who says there will be ramps next year.... or bumps... (or dry land for that matter) :cool:

On a more serious note... Is that a sprocket or a gear on the center wheel?

If you aren't gonna power the outer wheels why not get rid of chains all together and incorporate the wheel directly into the tranny?

What trannys are you planning to use anyways? The kit ones perhaps?

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I saw your request. I have go run some errands and then draw it up. Really, a few inches inside the frame will work. I'll try to autocad it up quickly.

EDIT: As promised, here is a drawing. Of course, you can move the tubes to wherever you want, but towards the ends makes it the strongest, however, having it on the very end may not be the best idea because your mechanism may not be able to work properly.

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I agree, center wheel drive is limited because it cannot climb ramps. However in a game without such obstacles (eg. 2002, 2005, 2008) center wheel drive is fine. Other years, some teams have used a drive system that cannot negotiate obstacles, and have still done well. eg: cheesy poofs in 2004. They could hang on the bar without climbing the stairs.)

Figuring out how to power the corner wheels is not the issue. With a few more sprockets, some chain and moving the inner rails, i could have a 6wd. However, this design is not 6wd, its a design similar to what 1519 has used for 3 years.

I'd like to point out a few things
-We don't know the 2009 game and we don't know what kind of drive system will be best for this game.
-Both 6wd and center wheel drive have their advantages and disadvantages.


I'm planning on using either Dewalts or AM toughboxes.

Its a 36 tooth sprocket.

Interesting idea... To be honest, i didn't really think about a direct drive that way. Mounting the tranny output shaft to a wheel is easier said than done. Especially on the toughboxes. It would be pretty easy for something like the Banebots p80 long shaft. But because the toughboxes have such a short shaft, you would need an extension. something to think about.


With all the comments from everyone, I think i'll start working on another design...

DB

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AM makes an extended shaft for the supershifter. It actually wouldn't be too complicated at all to modify that shaft for a toughbox. If you want further info, download the cad files of both and look at how similar they are.

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We did that this year, a pretty simple operation to do on the lathe.

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Now, don't automatically go thinking that a lighter chassis is a better chassis.

I explained in another post that having a relatively heavy chassis isn't always a bad thing. It basically forces you to make a lighter manipulator, basically meaning that your CG will be closer to the ground.

For the past two years our chassis (...I've never used the plural form of chassis) have been in the range of 80-90 pounds. We haven't tipped once in those two years.

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Just a little lesson here.

1 x1 x 1/8" aluminum tubing weighs 0.5132 lbs per foot

1x1 80/20 weighs .5097lbs per foot

so in this case your design weights more than with 80/20 now this doesn't take into account the hardware weight. Also 1x1x 3/16" is not a common size for tubing typically it comes in 1/16 or 1/8"

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Thanks for the specs. I confirmed those weights here and here.

Thanks for pointing this out!

Now that i look at my CAD i realize i made a mistake. The square tubing is actually 1/8 thick, not 3/16. It was those dead axle angle brackets that are 3/16. My bad.

I guess i thought 8020 was heavier, and never bothered to weigh it. Although this design with 8020 weighs pretty much the same as a design with 1x1x1/8 tubing, the hardware is the killer. I was planning on TIG welding the square tubing frame, which adds only a very few ounces, and provides a very strong bond. the 8020 brackets are a little heavier. 12 of these brackets would weigh about 1 lb. and still probably wouldn't be as strong as a weld. Then again, a pound or two is a small price to pay for the ease of use that 8020 provides.

I'll certainly look into a direct drive for the super shifters and toughboxes.
I'm guessing this is the long shaft you were mentioning.

DB