pic: Rookie Testing Platform

[ubermeister]

Originally Posted by Rupnick

As for the X vs O thing.
Mecanum can be used in 2 different "orientations" we played with this for the 2007 season. X gives you more turning but less strafing, O gives you more strafing less turning, so thats how that works, your not "wrong" but you may not be using the orientation you need for the specific game.

I'm pretty sure both orientations would give you the same quality strafing, but that you absolutely need an X on top.

The reason is that with O, your rollers on the bottom look like an X. Since the rollers roll perpendicular to their axle, X on the bottom allows the robot to spin around freely. This doesn't sound like much of a problem (until you're getting spun around on the field), except for this:

You can't turn under power with X on the bottom. All the force that would be turning the robot is redirected by the rollers into an X pattern rather than an O pattern. So the robot is really pushing inwards on itself when it tries to turn, rather than pushing itself around.

Sorry if that's confusing. The bottom line is that O on top doesn't allow turning at all, and rather causes the robot to skid and jump around. You need X on top if you want to turn.

[Alan Anderson]

Originally Posted by ubermeister

You can't turn under power with X on the bottom. All the force that would be turning the robot is redirected by the rollers into an X pattern rather than an O pattern. So the robot is really pushing inwards on itself when it tries to turn, rather than pushing itself around.

If your mecanum wheels are placed in a rectangle rather than a perfect square, you actually can manage to turn if they're installed with the wrong orientation. The vectors won't all cancel completely unless all the roller axes intersect at a single point.

They still cancel to a large extent, and it still doesn't turn very well.

The proper configuration has the rollers angled so that each of the wheels could move freely in a direction toward or away from the center of the robot without the wheel itself turning.

[Dowjonesbotics]

I would use the smaller wheels if u decide to use mecanumatic wheels.