One way to get this effect is make a ribcage inside the character that can expand in and out when a cam shaft rotates. Sadly I can't find any examples of this type of mechanism at the moment. But if you look at how cam shafts can work with linkages you should be able to visualize some solutions.
Answers
One way to get this effect is make a ribcage inside the character that can expand in and out when a cam shaft rotates. Sadly I can't find any examples of this type of mechanism at the moment. But if you look at how cam shafts can work with linkages you should be able to visualize some solutions.
/Chris