The Secret to Smooth Robotic Movement

In this video, researchers unveil a breakthrough in robotic motion using stretchable electrohydraulic artificial muscles. Inspired by the elegant, full-range movements of animal joints, the team tackles a key limitation in current soft actuators—lack of stretchability. Traditional electrohydraulic actuators (Hazels) can contract but not extend, hindering their ability to mimic natural muscle behavior, especially in antagonistic pairs like biceps and triceps.

To overcome this, the team introduced stretchable electrostatic clutches, creating a muscle-clutch unit that can both contract and elongate. These new units operate in four controllable states, enabling synchronized, lifelike joint motion. Experiments show that this design dramatically improves range of motion—restoring up to 50% lost with traditional slack-based solutions—and performs consistently across frequencies. This innovation brings robots one step closer to moving with the fluid grace of living beings.

Transcript

00:00:00 in this video we present our research on stretchable electrohydraulic artificial muscles our work focuses on achieving full motion ranges in muscular skeletal antagonistic joints animals exhibit complex elegant movements resulting from simple muscle contractions replicating this natural Elegance in robotics is a significant

00:00:26 challenge our work explores using artificial muscles in robots to replicate the fluidity of animal movements electrohydraulic soft actuators or Hazels are artificial muscles that contract when voltage is applied by stacking them we achieve the necessary force and displacement to build muscular skeletal robots however to truly mimic natural movements we must

00:00:49 consider how muscles operate in antagonistic pairs when we lift an object our biceps contracts while our triceps elongates this coordinated action enables the elbow joints to achieve a full range of motion a key limitation of Hazel is their inability to elongate due to their non-stretchable materials this limits their ability to fully replicate

00:01:13 natural muscle movements let's consider an antagonistic joint like our elbow powered by non-stretchable artificial muscles with just one muscle the limb can only move in One Direction when we add the opposing muscle we run into a problem the motion gets blocked because the muscles can't stretch the usual fix is to add some slack in the tendons but this comes at a cost it significantly

00:01:38 reduces the range of motion cutting it down by at least 50% to overcome this limitation we developed an antagonistic muscle system capable of both Contracting and extending we achieved this by adding stretchable electrostatic clutches to our design these clutches provide strong blocking forces even at low voltages which make makes them ideal for use with

00:02:01 electrohydraulic actuators by combining them in series with the muscles we formed a muscle clutch unit capable of shortening and elongating each muscle clutch unit operates in four states based on the on or off positions of the clutch and the Hazel actuator by synchronously controlling these units in an antagonistic setup we replicate the full

00:02:22 range of natural muscle movements something that is not achievable with hazel muscles alone our experiments showed that arranging the muscle clutch units antagonistically enhances the range of motion by minimizing the displacement loss due to tendance slck without the electrostatic clutches using only electrohydraulic muscles the range of motion is significantly

00:02:45 limited we also tested our system at various frequencies the results indicate that using electrostatic clutches consistently increase the range of motion compared to muscles without clutches