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1. Use cardboard box’s as a target for your wrecking ball.
2. Make the boxes at the bottom heavier so they are much harder to knock over. Just add a little sand to the box.
3. Make the wrecking ball from a ball on string and then put it on a rod between two bamboo uprights facing the wall so that you can move the string along the rod to take aim at the wall.
4. Use bamboo and string with a pulley to make a crane arm that can lift a bucket up and down. You will need to make it swivel so that the arm can move from one place to another and then lower the bucket of sand down again.