I've been trying to make a spaceball too no one will tell me how much it has to weigh so i can fall with it on my belly. I used a tennisball with pennies in it and a pullup cord to slow it and make it fall straight. I just need the right weight. 99pennies is a good weight for head down ive heard. good luck and put yourself out over a feild when you jump make sure if you lose it you lose it over an area of nothing to ensure no harm to people or property