Social robots are increasingly being deployed in public environments. However, few studies have suggested ways to design robot upper body and body vertical-oscillation to enhance the robot’s emotional expressions during ‘walking’. This study presents a novel body-avatar interface (BoAI) enabling real-time mapping of human movements onto a robot. Using this interface, participants designed emotional upper body movements for the robot. Further, drawing inspiration from vertical oscillations in human emotional gaits, we propose emotion-specific vertical oscillation patterns for the robot. To evaluate the robot’s resulting emotional expression, two video-based subjective studies were conducted with 307 and 869 participants respectively, by utilizing Mean Opinion Score (MOS) and Godspeed questionnaires. The results demonstrate that our proposed emotion-specific vertical oscillations significantly enhanced the robot’s perceived emotional expressivity, anthropomorphism, and animacy during walking compared to neutral motion. This paper makes key contributions in designing emotional expressions for mobile robots. The BoAI and emotion-specific vertical oscillation patterns open new possibilities for improving robots’ ability to express emotion during ‘walking’, offering possibilities to expand social robots across diverse interactive scenarios.