Locomotion analysis of a 3D printed electronics-free peristaltic soft robot

Soft pneumatic peristaltic robots inspired by earthworm locomotion offer advantages for navigating confined and unstructured environments. However, most systems rely on electronic control architectures that increase complexity, weight, and deployment constraints. Pneumatic logic gates (PLG) enable electronics-free control, yet their application to peristaltic locomotion remains limited. Here, we present a comprehensive study of a 3D-printed, electronics-free peristaltic soft robot controlled by integrated PLGs. We first characterize the switching frequencies of PLG-based ring oscillators that generate distinct wave patterns. We then analyze locomotion across wave pattern, direction, medium, and frictional contact, supported by simplified physical models linking pneumatic logic dynamics and wave propagation to performance. Two configurations are evaluated: passive bristles and actively retractable setae for friction modulation. Experiments on substrates with distinct frictional properties, along with real-world tests on exposed concrete and within a confined pipe, demonstrate locomotion beyond controlled settings. Retrograde waves consistently yield higher velocities, while friction and friction-control strategy govern gait effectiveness. Active friction modulation introduces adaptability but requires coordination to outperform passive designs. These findings provide design insights for electronics-free soft robots and represent a step toward deployable peristaltic systems.