LUGNET News : ~1048/GBC_lessons


Brian Alano / GBC_lessons_learned

Lessons Learned

Ball Handling

from: David Schilling, http://news.lugnet.com/org/us/smart/?n=286

A few things about handling balls: we’ve discovered that there is almost no simple hopper system that you can build out of Lego that doesn’t somehow jam. It’s impressive how quick the soccer balls can come up with a way to not go where you want them to. Almost makes you want to start believing in resistentialism! And if you have more than a couple of balls that you want to move along a path, you’ll discover the same thing. Even single balls will consistently stop moving anywhere along a path that has a turn in it.

The only system that seems to work somewhat reliably is to have some sort of active feeding going on. You need to be stirring or shuffling or shaking or scooping the balls to prevent a jam, and even then it’s more of a ‘mostly prevent’ than a sure thing.

Crate Size

from: David Schilling, http://news.lugnet.com/org/us/smart/?n=287

Usually we aim for around 30 balls per crate. That gives enough leeway that if a robot is out of commission for a few minutes (changing batteries, say) that a ‘filling’ robot still can run without being stopped. More than around 60 balls and the crate overflows.

If the crates were shorter then you’d have less margin for error. You’d likely have to stop any filling robots upstream if a robot goes out of commission downstream. And any robot that drops balls in from more than just above the crate edge will start having balls bounce out. Originally we were aiming for around 50 balls per crate, but the problems made us reduce that number so that things would work more reliably.

Crate Shape

from: David Schilling, http://news.lugnet.com/org/us/smart/?n=287

We talked about different mechanisms of lifting crates at one time, which would have entailed a redesign, but the most reliable way was to grab the top edge of the crate while also holding it underneath, something which our crates already did pretty well.

See also The GBC Index.

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