Move a platform lifter, excavator, robot arm without using any type of electricity! Compete with your friends to see whose machine can finish the mission!

baloons 
towels
food coloring
containers for water


http://www.youtube.com/watch?v=ofsIMCZgzcY

VEERY GOOD
http://www.youtube.com/watch?v=YlmRa-9zDF8&feature=related
http://www.youtube.com/watch?v=UuK3ESGgbqk&NR=1