Engineers underactuate a robot to save weight, reduce physical complexity, and lower manufacturing costs. Instead of placing a motor at every single joint, the system relies on passive dynamics, springs, or mechanical linkages to govern the unpowered joints. This approach requires highly sophisticated control algorithms because the robot cannot directly command every movement, relying instead on momentum, gravity, or mechanical coupling to reach the desired state.
If we underactuate the gripper by driving all three fingers with a single tendon, we drop the payload weight by a hundred grams but lose individual finger control.
While the verb is used during the design phase, you will almost always hear this concept used as an adjective, as in an underactuated hand or an underactuated biped.
Related terms
Fin gripper
A compliant robotic end effector that bends inward to wrap around objects when pressure is applied.
Model-based design
A mathematical and visual method for developing complex control systems before building hardware.
Multigait
Capable of using several different walking patterns to traverse varying terrain.