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Originally Posted by Jared341
Can somebody explain the physics behind the "intake must run at >=2x robot speed" assertion? I've heard this before, and even designed with it in mind, but only now do I stop to think about it.
Intuitively, I don't see why running at >1x robot speed wouldn't work?
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If you draw a ball and imagine it rolling at 1 m/s. At any moment in time, the bottom of the ball is stationary (in contact with the ground). The middle of the ball is traveling at 1 m/s. This means the top of the ball is at 2 m/s.
With a collector that touches the ball, it is the same. If the collector has the same surface speed as the robot is traveling, it will want to puch the ball forward as it draws it in. If the surfaces speed is 2x or greater, it will draw the ball into the robot. This is best seen with the backspin collectors when they are backing up. If the surface speed is 2 m/s, the robot will loose contact when its back-up speed is greater than 1 m/s. The ball still has some momentum and will continue towards the bot if the bot stops.
Normally the collectors suck the balls into some sort of feeder system. This year, there is a 3" intrusion rule. High speed collectors impart a lot of energy into the ball. This energy can cause a bounce when the ball hits its backstop. Some teams fixed this by moving from a top-spin to a lower point along the side of the ball. This reduced the rearward momentum, but induced higher normal forces between the ball and the carpet. This meant that you needed more power to keep the ball backspinning. The solutions for that were either a clutching mechanism (so that the ball did not backspin of which 1918 was extremely creative), more powerful motor, or larger ratio which meant slower surface speed. The topspin systems often used some sort of cushioned backstop to absorb the extra kinetic energy, or would have a cushioned roller mount (our original topspin, backspin system) with a lower idler roller.
With the high surface speed that 910 has, I imagine the had lots of testing with the ball rebounding out of the machine. It looks like they found a very interesting solution of compliant yet slick material. Again why that was my favorite collector this year.
If you need some diagrams, I can throw together another Powerpoint. I have a few decks of slides from our collector studies. I would have posted it up, but felt kind of silly saying, "Yeah, we did all this engineering to get this one design which was sort of OK, but then went with a design we ruled out in week 2 because we saw it was better in a video".