Pinching a 9 inch soccer ball at two points within the allowable 2/3 portion is very tricky indeed. Just holding a soccer ball with two tacky parallel cylinders is not easy. We found balancing the "dynamic" forces is very difficult (air pressure in the ball, static and rolling friction, etc.). Although I do not have a PhD in Physics, I am convinced that simple force diagrams will not capture all the variables - especially when the robot is moving. Experimental confirmation is key here.
During our prototyping, we could not find that delicate (favorable) force balance required for an approach like yours. It appears that you found the sweet spot. Congratulations.
-- to all other teams, "there is another". Looking forward the NJ.
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Originally Posted by Paul Copioli
With regards to the ball magnet, think of it this way:
If the normal force between the ball and the floor is less than the normal force generated between the ball and the "magnets", then the ball will stay possessed by the robot. This doesn't mean the normal force between the ball and the floor is zero.
The instance you see in the video near the goal was an implementation issue that has already been resolved. The ball will always be touching the floor when the magnet is on.
I can tell you this: we (148 + 217) created the ball magnet concept using only 9th grade geometry and 11th grade physics (1st semester).
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