hi,
I am helping out some juniors who are taking part in a robotics competition. to, cut the long story short, the objective is to pick and place 3 colored boxes at their correct location while navigating via line following.

box dimensions
currently , we were thinking of making a arm+gripper (only 1 link) that would clamp on from top, using protruding ledges as support point for the gripper.
an alternative would be to utilize the holes to lift it up.
i would like to know your idea about a sturdy arm+gripper that could work best, with weight of the boxes being 400-450 gm, since the box needs to be 'lifted' from the ground during the operation. would there be any other way to do it other than a manipulator?
thanks..!