Quote:
Originally Posted by Bjenks548
This is why I'm confused. Let's say that you do have the design I mentioned, if you drive both forward you drive forward because the right wheel is pulling forward and left, and the left wheel is pulling forward and right. Therefor left and right cancel out (assuming same speed). Same can be said for driving both backwards. Now if you drive the right wheel forward it pulls forward and left, and the left wheel backwards, backwards and left. Shouldn't you go left? And running the right one back and the left one forward shouldn't you go right?
As I see it the only reason i would need 4 mecanum wheels is to turn, not to strafe.
Someone explain to me how I'm wrong considering no one else sees this happening.
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There's a good way to visualize how this would happen too. Imagine a merry go round you might have had in a playground growing up. Now, put a person on the east (right) and west (left) side of it. If both people push north, it doesn't spin (ie the robot would go straight forward). However, if the guy on the east pushes towards the North West, and the guy on the West pushes towards the South West, they can spin the merry go round (Because one is pushing towards the north and the other towards the south). It's not a perfect spin, however, because they aren't pushing tangentially to the merry go round - some of the force goes into translation.
This analogy isn't perfect, as it's hard to visualize that translation with it. But it does a great job with rotation. For a normal Mecanum drive train (with 4 Mecanum wheels in the corners), you can stick people on the North East, North West, South East and South West corners and have them push in different combination's. You'll find that when they're all pushing tangent to the merry go round, in the same direction (clockwise or counter clockwise), the merry go round will turn without translation. And when you have them working in opposing pairs there won't be any rotation, but the force has to go somewhere - you should be able to figure out what the translation would be.
In physics, this is called a free body diagram. You imagine your forces acting on a pivot arm coming from the center of mass of your object (arguably the center of your robot, for all practical purposes... although your mileage may vary based on specific robot designs). If the forces line up properly, they'll cause the object to rotate or translate (or both!). It's one of the more important concepts in physics, and one that students seem to have the hardest time grasping.