In the past few years, we have covered a whole host of Boston Dynamics robots including Spot here. These robots are not cheap, but you can always build a smaller version of them powered by a Raspberry Pi. Take Spot Micro for instance: it is a quadruped robot that runs custom C++ and Python code on a ROS Kinetic framework.
As SpartanIIMark6286 explains, the robot is built with a Pi 3B, PCA9685 servo control board, 2s 4000 mAh LiPo battery, and a 3D printed body. You can find the code and all the relevant information on GitHub. Pretty neat, don’t you think?