In this instance the high speed motor is equipped with a brake. In some version the high speed motor use an irreversible gear reducer, saving a component but at the cost of backdrivability.

@@AlexandreGirard87 something like electromagnetic brake would work? I wanted to use it, buy I'm afraid that electromagnets aren't designs for continuous work, if i wonted to use high torque mode for a long time.

Here this prototype was using a normally closed em brake. Hence it was using energy only when unlocking the high speed motor.

Thanks, yes robotic legs are clearly one application. Here in the experiment the trigger was based on a simple deceleration criteria but for a more generalizable trigger a force sensor would be an option.

@@AlexandreGirard87 Thank you for your explanation sir. Actually, I saw a paper of your research regarding the planetary gear based gear shifting mechanism and so fascinated about your approach. I'm a Ph.d student in KAIST south korea working on variable transmission and got inspiration from your research articles. Thanks😄