we have a small piece of lexan that holds the boxes at the top, but we don't really need it, for picking up a stack at least. we've tested with less than 4 bins, and they seem to hold ok.
i came up with a way to stack based on our design, but it was an afterthought, not a design feature. so, yes, we can stack. can we do it in the thick of competition, that remains to be seen.
lastly, we can theoretically pick up any stack, regardless of if it's up against a wall, i think. i haven't been able to test it, maybe another member of my team has more detailed answers, but i can't answer that question, at least till competition

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