Like most consumer robots, Pleo runs on batteries. These nickel metal hydride (NiMH) batteries are inflexible, and they take up a lot of room, so they have to go in the largest part of Pleo's body -- his abdomen. This made realistic movement a challenge. Sosoka explains:
When you are walking behind your dog, they are making like this S-curve. They are swaying back and forth, and it's really compelling to be able to move like that. When you put a pivot right in the middle [of a robot], you lose this wonderful big space where you could put all your boards, your batteries and everything.
The result was a removable battery pack that didn't interfere with the pivot in the middle of Pleo's back. The battery pack uses nickel metal hydride (NiMH) batteries and has a four-hour charge time for an hour of battery life.
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Another challenge was Pleo's tail, which is central to the appearance of emotions. The trick was to make the tail movable while making it sturdy. Sosoka describes the tail's movement:
So there is strong steel wires, like a little marionette. They control the tail. [There are] four wires, and the horizontal ones oppose each other and the vertical ones. You can do whatever combination and curl the tail up. So those wires are pretty strong ... Picture a piece of nylon running down inside of all the vertebrae. We captured it at both the ends so that it could absorb some of the tension.
Motors move these wires in response to instructions from his processors. The motors also move Pleo's head, neck and legs. Clutches and force-feedback sensors in his legs help protect his components and provide responses to obstacles he encounters. "Pleo has clutches in all of his motors so that if he lands on his feet, his feet can give a little. They don't transmit all of the pressure. Those clutches also allow Pleo to know that you are messing with [his leg], and then he can cry out or limp," Sosoka says.
Out of the box, a Pleo has the ability to explore and learn from his environment. But Pleo also has the ability to be programmed and customized. We'll look at how this works on the next page.