My daughter play with the cat for about 15 minutes,the batteries get hot,and the plastic case close to the negative pole get melted and pop out. I fix it with hot glue and cut the springs into half length. I also notice that the number 12servo connected to pin 7 is hot even just turn on the power for ten seconds,but it is normal in function.
I know the reason for the hot servo now. When I turn on the power and hold the cat with its head up, it will keep a gesture to keep balance, and its front left shank keep rising up against its should, so the servo gets hot in a short time.