What does it take 6WD/8WD to be successful?

[TEE]

Basically what the title says... what does it take to make a great 6 or 8 wheel tank drive?

[keehun]

Driver Practice.

[TEE]

Any robot takes driver practice to be successful... some more than others...

I was asking in reference to the the construction of such a drive, and not just any 6 or 8 wheel drive, one that really gets the job done.

[Akash Rastogi]

Originally Posted by TEE

Any robot takes driver practice to be successful... some more than others...

I was asking in reference to the the construction of such a drive, and not just any 6 or 8 wheel drive, one that really gets the job done.

Specifically what type of 6 or 8wd? Drop center? Omni + traction? direct driven?

Its a bit too vague of a question and not really one that has a real answer to it.

I've seen teams with kit drives that "get the job done." As long as it doesn't fall apart on the field you're basically good.

.

[TEE]

Sorry for the ambiguity...

I've seen teems with tank drives that are relatively slow and don't turn well. With direct reference to a 6WD/8WD, I meant one without omni's that still turns quickly, and that has a 2-speed transmission to be able to push well in low gear and move quickly in high gear.

Is drop center better? Would Omni's in front and back be better? What gear ratios would work best? Is it worth it to use FP motors?

[EricH]

What is "the job" that needs to be done?

What is your definition of successful?

[Chris is me]

Not much. You want a dropped center, a good transmission (shifting usually so you can get 9fps safely, more or less depends on the game), and practice.

Dropped center is better than omnis because when you get pushed, you'll "rock" onto that side and won't be spun nearly as easily as an omni based drivetrain. I personally like 8wd because the rock has less of an effect on driving, but it's probably not worth the added weight and complexity for most flat games.

[Andrew Schreiber]

The KOP Frame, KOP Transmissions. Read the instructions. No, I am not kidding. You can save a bit of weight by doing it all custom but since you already have an effective solution why not use it?

Build it week 1 and get people practicing. Work your kinks out early.

Fail Faster
Learn More
Focus and Execute

[Alex Cormier]

It's mostly based on the game for the year.

There is also this thread too.

[TEE]

Originally Posted by Alex Cormier

There is also this thread too.

which thread?

[ttldomination]

A 6 WD with a dropped center does its job. We made a 6 WD with a dropped center using a standard toughbox, and that thing was crazy. It was quick, zippy, and the torque was crazy. As per a 8WD, I think that the were dominant this year because teams didn't want to bottom out on top of the bump. But usually, you'll see 6 WD.

As for gear ratios, read this post before you think of something crazy. I personally agree with this logic. One can always find a nice balance.

[Jamie Kalb]

Originally Posted by Andrew Schreiber

The KOP Frame, KOP Transmissions. Read the instructions. No, I am not kidding. You can save a bit of weight by doing it all custom but since you already have an effective solution why not use it?

Build it week 1 and get people practicing. Work your kinks out early.

Fail Faster
Learn More
Focus and Execute

This method worked really well for my team this year. The kit base is highly underrated. It's not perfect, but it's a lot better than people seem to think. Having a working chassis with almost zero design time was huge for us. There was only one major thing I felt was missing, and that was chain tension. Maybe we were doing something wrong, but we never could seem to make the chains happy; they were always too loose or too tight. One of our freshmen got really good with the chain breaker, because he had to use it daily . If only the kit chassis had an integrated tensioner system, I'd try to use it every year.

Edit: The kit chassis does have a tensioner system, but I feel it's not implemented well. The mount bracket for the Toughboxes has slotted mounting holes, so you can pull it one way or another to tension chain. The problem is that if you do everything by the manual (standard 4WD), you'll have two chain runs coming from the Toughbox output shaft in opposite directions, so when you tighten one, you'll be loosening the other. You can get around that with some creative chain routing, but my point is that there isn't a really good tensioning system already integrated.

If I was trying to design the ultimate skid-steer drive, I'd make it somewhat like 254/968/27 style (West-coast drive), like 221's Universal Chassis. If my aim was anything less than "the ultimate skid-steer drive" (if I had limited resources, etc.), I'd go with the kit chassis, 6WD, dropped center (there's already a lowered hole for this in the kit chassis's side rails), and spend my design time creating a great tensioner system.

My $0.02

[Wayne TenBrink]

A few items to consider for a good 6 or 8 wheel tank drive (or any other chassis, for that matter):
1) For better turning, keep the track width (side/side spacing) large relative to the wheelbase (front/back spacing). For a long aspect ratio chassis, this requires either lowering the center wheels or using omni wheels at one (6WD) or both (8WD) ends.
2) For better stability, keep the wheelbase long relative to the track width.
3) Ideally you want a good balance between turning ability and stability. A wide aspect with wheels at the corners, or a 6WD with dropped center wheels is about right. If you can fit more traction wheels between the other rigid (non-omni) wheels, that is good and can be done without lowering them.
4) Keep the wheels as close to the frame perimeter as possible.
5) You will spend a lot more time turning, lining up on a game piece, accelerating, and pushing than you will going fast. A "slow/strong" single-speed is usually better suited than a "fast" single-speed, and simpler (to build and drive) than a two-speed.
6) Develop and test chassis designs during the fall/off-season. Try to develop a "system" (chassis structural modules, gearbox mounting, chain tensioners, axle mounts, maintenance & repair accomodation, etc.) that can be adapted to a wide variey of final configurations (wide/narrow, # drive wheels, wheel
size & type, ground clearance, etc.). After kickoff, it is relatively quick to finalize the design and get started on building the "bottom end" while you are still figuring out the "top end" (manipulator). We build our own chassis's and are usually driving by the end of week 2.

[IKE]

Step 1: Figure out what you want it to do.
Step 2: Figure out what it takes to get it to do what you want.
Step 3: Figure out how to make what it takes.
Step 4: Adjust your strategy if you can't make what it takes.

Most successful designs follow this process. One of the most successful strategies/designs ever was drive fast, drive straight, have amazing pushing ability, hold position.

So Tee? What would you like your 6x6 or 8x8 to do?

I would give you drastically different advice depending on the game. While our chassis from 2006-2008 look very similar, they have very specific attributes that were very specific to the games those years.

[dtengineering]

Its more than just hardware... it's also in the software.

Put a gyro on your robot and you can make sure that it drives straight, even when you've got unequal drag on each side... or when you're being bumped. A gyro can respond more quickly and accurately than a driver.

We've also found that using seperate control sticks for Forward/Reverse and Left/Right can help tracking. That way, when using "arcade" style driving (rather than tank style, where you control each side or the robot with a seperate stick) when you want to go straight forward you just lift your thumb off the "turning" stick, and you will always get a perfectly straight forward/reverse input to the robot. When you want to stay still and turn, you take your thumb off the forward/reverse, and all you get is turn. Sure... you can tune your deadbands and all that, but this is what we've found to work best.

Jason