ACM-R4by Shigeo Hirose and Hiroya Yamada (2004). The number of joints it is realistic to build in a robot snake is small compared to the hundreds of joints in a real snake. To improve manoeuvrability and make a practical robot, the R4 retains the flexibility of a snake but adds active wheels so that it can move without having to resort to serpentine motion. It’s also water and dust-proof, making it useful for dirty jobs like pipe inspection.