Hydraulic vs. Electric Actuation: The Power Density Tradeoff

Why the industry's broad shift to electric actuation involved giving something up, not just gaining.

Hydraulic actuation uses pressurized fluid to generate very high force in a compact package, historically giving hydraulic robots (the early Boston Dynamics Atlas being the clearest example) exceptional strength and dynamic capability. Electric actuation uses motors and gearing instead, trading some peak power density for efficiency, cleanliness, and much simpler maintenance.

Why the industry shifted toward electric

Hydraulic systems need a pump, fluid reservoir, and plumbing throughout the robot, all of which add weight, complexity, and maintenance burden, plus meaningful energy losses from fluid friction and heat compared to a more direct electric drivetrain. As electric motor torque density improved, the balance tipped toward electric actuation for most commercial applications.

Where hydraulics still holds an edge

For applications demanding the highest possible power density in a small package — very rapid, forceful, dynamic movement — hydraulics can still outperform current electric actuation, which is part of why some newer platforms have explored hydraulics again despite the broader industry trend toward electric.