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Re: How can you make turning smoother?
Let's assume you have a robot frame with electronics and the center of mass is directly in the middle of the robot, a few inches from the floor. Let's say it weighs 30lbs. Now, you add the battery (assume 15lbs), which is equidistant from the two center wheels and the two rear wheels.
Let's say you're spinning it slowly such that centripetal force is negligible. There is more normal force on the center wheels than the outer wheels because the center of mass is somewhere between the battery and the center of the robot (and more toward the center at that). This means there is less frictional force applied to the outer wheels and they will effectively "skid" across the floor, allowing you to turn on a dime.
If you increase the turning rate and take centripetal force into account, you are applying a force on the frame that is opposing the centripetal force on the battery.
Imagine you have a heavy weight on the end of a string that is attached to a vertically mounted pole. When you swing the weight around the pole (think tetherball), the weight indeed rises. However, the robot isn't the weight in this scenario. The robot is the entire system, and the weight is the center of mass. The pole tends to lean in the direction of the weight because of the force opposite centripetal force that is being applied to it. The same thing happens for FRC robots.
I believe it's much less noticeable because the dynamic friction is less than static friction in the case of wheel tread and with a robot weight mostly centered but off to one side, the center wheels will never start slipping. I have seen Vex robots with six wheel drive behave like four wheel drive robots, because the center of mass is either equidistant from the four wheels in contact with the floor or more toward the outer wheels.
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