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Originally Posted by Kevin Sevcik
That's only true in the static case. It's possible to save a situation that would statically be a tip by accelerating or decelerating, which is the equivalent of pushing the CoM one way or another. You can also cause a tip in the same fashion.
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Acceleration is a force and therefore would affect the direction of your footprint projection. The footprint is projected in the direction of all forces acting on the robot, I just said gravity because that is always present.
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A heavier robot with more rotational inertia is going to tip less than a lighter one because your motors stay there same. I guarantee you I could build a chassis that flips due to its own wheel force, and fix it by adding weight without changing CoM.
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This would prevent the tipping because it would reduce the robot acceleration, and rotational acceleration (which means it would have to undergo lateral acceleration for longer before reaching its tipping point) therefore changing the footprint projection, that's the real reason it wouldn't tip.
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Originally Posted by marshall
Yes but I believe the static case for that occurring and the dynamic case are different. When stationary we could pull our robot back to quite a degree without it tipping over but when we attempted to cross defenses the robot turned into a pendulum and it tipped. Adding ankle weights at the four corners prevented it from happening again. Our COM was already low so it wasn't just the COM that needed to be adjusted to fix the tipping issue.
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As mentioned above, the cases are the same, you just add another vector for robot acceleration.
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Originally Posted by mateoland
The problem I saw with the higher robots was not necessarily that they would tip, but that so much time was spent waiting for the teetering to dampen out before being able to drive again. It plagued a couple of teams in Los Angeles. If they hadn't waited a moment to let the back and forth movement settle, they would have most likely driven "under themselves" and tipped backwards. Precious seconds lost multiple times in a match.
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Very true, the reactionary force when the robot stops makes it like a pendulum, you want to accelerate out of phase with the robot tipping period to not magnify it.