The basis of Sophia's leg design, including control software and state-of-the-art sensors, is based on a Korean social humanoid robot named Jaemi-HUBO (HUBO 2), the predecessor to the award-winning DRC-HUBO, a relief robot that can either walk or roll using wheels on its knees. Jamie-HUBO and Sophia's feet are similar to DRC-HUBO's feet, but both are smaller and more focused on social interaction. For example, Sophia's legs were customized to match her height and weight to match the proportions of her torso and increase her stability when walking.

You may be familiar with another famous HUBO robot with similar robotic legs, Albert HUBO, also developed in collaboration between KAIST and Hanson Robotics.

Sophia's legs are powered in the same way as the DRC-HUBO and Jaemi-HUBO, with twelve 48V motors, totaling six for each leg. The two power sources are the main power board on her back and the battery packs on her legs, which also power her torso and head.

There's a reason it's called PODO software

To control Sophia's legs, a version of the PODO software, originally designed to control DRC-HUBO and Jaemie-HUBO, is customized. PODO means "grapes" in Korean, so the software is aptly named as each program can be integrated and removed from the main root quickly and easily. In this way, each independent program or algorithm comes together like a bunch of grapes. A real-time robot control system allows multiple people to work independently and simultaneously.

In the humanoid world, one of the constant research is the ability to traverse uneven terrain. What humans typically consider "flat" terrain can have many differences, including slopes and small bumps or depressions in the ground that are difficult for humanoid robots to navigate. The PODO software, however, incorporates state-of-the-art walking algorithms, such as model predictive control (MPC) walking, which allows the controller to respond to future disturbances before they occur. This allows Sophia to keep her balance while walking on uneven surfaces, including slopes or changes in floor material.

Hardware Perspective

Sophia's leg design includes some of the most advanced and top-of-the-line sensors in the world. These sensors include a state-of-the-art Inertial Measurement Unit (IMU) that allows Sophia to measure its acceleration, speed, balance and trajectory. Sophia's legs also have force-torque (Nm) sensors on them that allow her to "feel" how she is walking based on the forces acting on her body and then adjust accordingly. In other words, for each step she takes, Sophia looks ahead for obstacles, calculates her balance and trajectory, and then makes adjustments to avoid slipping or tipping.

What Sophia's mobility means

Giving Sophia mobility through her robotic legs allowed her to become more autonomous and experience the richness of the physical human world. Similarly, a walking social robot will allow people to interact with Sophia in a completely different way. According to Hanson Robotics founder David Hanson, "Integrating Sophia into a (robotic) body that allows her to walk completes her physical form so that she can have the full range of human experiences that will help her learn to live and walk among us."

With hundreds of hours of development, state-of-the-art software, advanced sensors, frequent adjustments and calibrations, Sophia can accomplish what humans do without even thinking: walk.