They are both nice designs, thanks for sharing them.
59990Z robot probably would drop some cubes during a match if there isn’t a dedicated stop. Also I don’t know if the robot’s holder starts diagonally to fit in 18x18x18, because if it doesn’t it should and probably could hold a couple more cubes. The mechanism to move the holder up and down could be greatly improved through the use of differential powered by the drive motors. This would free up a motor and make the mechanism stronger/faster.
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