Drives in general

[Gamerboyb1]

What would be the best kind of drives system:
Four wheel mecanum drive system
six wheel drive pivoting off the center wheel
8 wheel drive with 4 transmissions
6 wheel drive system with turning wheels

Thanks to all who respond it will help a lot!!

[ChuckDickerson]

You will need to define best for what a little more. "Best" depends on what your objective is.

[Gamerboyb1]

I would have to say for mobility and pushing power

[EricH]

All of them, plus all the options you didn't mention. Why? The game objective changes, so your objective(s) change. Different objectives need different equipment to obtain them. For example, a mecanum system can be good for precise positioning without having to back out, realign, and come back. The six-wheel dropped center design is a good all-around design, but it can have trouble with being easily spun when hit hard (which can be designed around).

Also, could you clarify what you mean by "6 wheel drive system with turning wheels"? I mean, all the wheels in a drive system turn normally; otherwise, the robot doesn't drive... Do you mean a combination of a crab system (all wheels rotate to allow the robot to go sideways without turning) and a six-wheel system, like the Chariot uses?

[Gamerboyb1]

sorry about that i was at a loss for words.
i meant a swerve drive system almost like a car set up.

[AndyB]

If you factor in mobility, pushing power, and drivability, I would go with 6wd. You get great traction, you don't need to worry about turning, and unlike a crab drive, the difficulty that a driver would experience is minimal. It's also easy enough to accomplish a 6wd with pretty much all kit and IFI parts.

The downside to 6wd is the weight of added chain and wheels.

[Gamerboyb1]

yeah but wouldn't the 4 wheel system give the best turning potential and pushing power because it would have more surface area with 2 more wheels?

[AndyB]

I'm assuming by 4 wheel, you mean 8 wheel.

Technically, traction is not affected by the change in surface area. The weight is just displaced. However, with the roughtop tread surface (if thats what you choose to use), your traction doesn't so much come from friction rather than the fact that the tread digs into the carpet. So yes, you may have more traction. Not that I've actual looked for it, but I can't say I've ever seen an IFI traction wheel slip on carpet with the roughtop tread.

As far as turning goes, you aren't pivoting on two wheels, you are pivoting on four which doesn't have much of an affect considering the distance between the pivoting wheels.

When it comes down to it though, 8wd's aren't as easy to make and of course the weight again goes up. I guess it all comes down to personal preference. The benefits of an 8wd in my opinion is outweighed by the weight.

If you look at last year, the teams with the best drives came from the likes of 330, 1114, 2056... etc. These were all 6wd 'bots. They all had extra weight for solid arms and ramps/swiss-army-knives(1114). If go by the logic of a perfect driver, I'd probably hand it to 4 wheel crab, but again, manufacturing difficulty goes up quickly. In the FIRST world, 6wd is easier to drive.

[Gamerboyb1]

no when i said 4 wheel i meant only four wheels.
I made a comment in the first post about a 8 wheel drive system

[lukevanoort]

Assuming that you mean just 4 wheel drive without omni wheels, pop-casters, or other such devices, then the answer is no. For the traction bit, as said above, for the most part, traction is independent of surface area in contact with the carpet. 4WD is a path with several pitfalls that must be avoided, and its maneuverability can turn into one of them. If a 4WD (again, assuming no omnis, pop-casters, and that kind of stuff) is longer than it is wide it will not turn well. On the other hand, a 6WD using the same wheels will always turn better (assuming the middle wheel is lowered or coplanar, not raised off the ground) than a 4WD of the same LxW dimensions. This characteristic along with the 6WD's inherent resistance to bottoming out on inclines are two of the major reasons that it is so popular among teams nowadays.

[EricH]

4WD often equals bouncy turns. It has to be done just right to eliminate that (usually omnis or casters, though the casters make it a 2WD). Almost the only easy way to eliminate this is to build a "wide" bot (the short side is front-to back), and then you have a tipping risk under normal driving. The most successful robot I have seen with 4 wheels is 69 in 2005. (At least, I remember them as having only 4.) They had very slick wheels, as I remember, so they slid a little bit.

[AndyB]

Originally Posted by lukevanoort

Assuming that you mean just 4 wheel drive without omni wheels, pop-casters, or other such devices, then the answer is no. For the traction bit, as said above, for the most part, traction is independent of surface area in contact with the carpet. 4WD is a path with several pitfalls that must be avoided, and its maneuverability can turn into one of them. If a 4WD (again, assuming no omnis, pop-casters, and that kind of stuff) is longer than it is wide it will not turn well. On the other hand, a 6WD using the same wheels will always turn better (assuming the middle wheel is lowered or coplanar, not raised off the ground) than a 4WD of the same LxW dimensions. This characteristic and resistance to bottoming out on ramps are what make the 6WD so popular among teams nowadays.

Thanks for clarifying. I forgot about the ramp part. The two out of three years, the game has involved getting up a ramp. If you consider getting unstuck from the tetra goals, then all three involved an some amount difficulty. With six wheels, ramps are not really a problem (assuming ground clearance) and you don't see many teams with 6wd getting stuck on parts of the playing field because you pretty much always have at least 2 wheels on the ground, if not four or six.

I have never worked with anyone, so if you have (Cyberblue ) on a hex drive (six wheels with middle wheels moved)

http://www.chiefdelphi.com/media/photos/27420

Do teams lower the middle wheel or is the point of moving them out so that they don't need to be lowered or lowered as much.

[Gamerboyb1]

no when i say 4 wheel i mean with omni wheels.
that would be a very big act of lessened intelligence to just use regular wheels.

[EricH]

I only know of one team who has tried a car-style steering. I don't think it worked as well as they hoped. (And I don't remember it doing well at competition.) Personally, I think car-style is a little too complex to do on a FIRST robot.

I think that most people are going to say either 6WD with dropped center or mecanum. AndyB is right on the money there; you can practically make one right out of the kit. I'm not sure that the extra weight is enough to be a factor; at least, if you design for it to be there, you can make adjustments before building.

EDIT: I don't understand your last question. Do you mean the 8-wheel system you proposed?