Double Support Phase

双支撑期DSPAdvanced

The part of walking when both feet are on the ground at once, as the body's support shifts from the rear foot to the front foot.

The double support phase is the part of bipedal walking when both feet are on the ground simultaneously, occurring between when the front foot has just landed and the rear foot has yet to leave; it happens twice per gait cycle, with the rest of the time spent in single support, when only one foot is down. Based on Wikipedia's figures for human walking — roughly 60% stance phase and 40% swing phase — the two double-support periods together make up around 20% of the cycle; this period shortens as walking speeds up, and disappears entirely in running, replaced by a flight phase where both feet are off the ground. For a humanoid robot, this period is the most stable: the support polygon covers both feet, the zero moment point (ZMP) must shift from the rear foot to the front foot during it, the two legs and the ground form a closed kinematic chain with more actuation than degrees of freedom (requiring a decision on how much force each foot contributes), and landing impact and contact switching happen right around it. Many simplified models treat double support as instantaneous, while more detailed gait planners explicitly optimize its duration.

ExampleA phase-based nonlinear MPC proposed by a Seoul National University team in 2025 jointly optimizes ZMP regulation, foothold placement, single-support duration, and double-support duration in one problem, and forbids updating the foothold during double support, improving a humanoid's walking balance against external pushes.

Also called: DSP, Double Stance, Double Limb Support
Related: Gait · Support Polygon · Zero Moment Point · Stance Phase / Swing Phase · Flight Phase (Aerial Phase) · Gait Cycle and Duty Factor
Sources: Wikipedia: Gait (human)
Phase-based NMPC for Humanoid Walking Stabilization with Single and Double Support Time Adjustments (arXiv:2506.03856)
Hybrid Zero Dynamics Control for Bipedal Walking with a Non-Instantaneous Double Support Phase (arXiv:2303.05165)