To prevent the yoalan from such an aggressive rocking. You can change the spring with a tighten tension, you can get it from Kiddy Palace with 6 spring attach. There is a rope to control the rocking height.ya, i understand, but i do not want dd to be too dependant on the yaolan. i also understand that if dd sleeps on the bed, it will cause troubles to my mil, so i'm thinking of buying a mattress to ler dd sleep on the floor rather than on the bed, also can prevent dd from falling off the bed. and one thing is, my mil always rock the yaolan so hard that dd is flying up and down inside the yaolan! told mil quite a few times already, she did improve, but forget again as days pass by.