Carnegie Mellon University
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Actuator with Mechanically Adjustable Series Compliance (AMASC)
This project is no longer active.
Head: Alfred Rizzi
Contact: Jonathan W. Hurst
Mailing address:
Carnegie Mellon University
Robotics Institute
5000 Forbes Avenue
Pittsburgh, PA 15213
Associated lab(s) / group(s):
 Microdynamic Systems Laboratory
Project Homepage
Our long-term goal is to develop robots that are capable of running, jumping, and stumble recovery, while being energetically efficient. The Actuator with Mechanically Adjustable Series Compliance (AMASC) is an actuation method that utilizes a large physical spring capacity and variable compliance, to enable such highly dynamic gaits.

This actuator is designed for use in the BiMASC,a highly dynamic legged robot. It has fiberglass springs with a large energy storage capacity. The mechanism has two motors, one for moving the position of the knee and the other for controlling the stiffness felt at the knee. These two parameters, along with the hip angle, are used for control of a running gait.

AMASC in motion

Closeup of cabling
Entire AMASC

Spiral pulleys
Fiberglass springs


Changing the stiffness of the AMASC 7.5MB

Zero stiffness (zero force) 5.8MB