Meet Ghost Robotics' adorable Minitaur quadruped robot.
Here's an excerpt from IEEE Spectrum's interview with Avik De and Gavin Kenneally, who are on the development team at Professor Dan Koditschek's lab at the University of Pennsylvania:
How the heck did you manage to get Minitaur to open that door?
De: I don't know if it's clear from the video, but there's a lot going on. The robot is jumping, it perceives that the door handle is there, retracts the leg, and manipulates the door handle.
Kenneally: Just to go over it in a little bit more detail: It jumps up on its front two legs, doing a handstand, and then jumps. The back left leg is waiting to feel the door handle, so it kind of sticks that leg out and waits until it senses contact. Again, all the sensing is through the motors, there's no current sensors or force sensors. Once it perceives contact with the door knob, it retracts the leg, moves it over a little bit, and then extends it, and that actually all happens within 50 milliseconds, so it's incredibly fast. And then once it's done that, the other back leg, which is now also in the air, pushes against the door to crack it open a little bit, and it also helps push the robot so it pitches back down toward the ground, where it then retracts the leg back and catches itself before it falls. The door opening and stair/fence climbing were done with help from T. Turner Topping. We've just submitted a paper on this these behaviors, and Avik has a bound paper forthcoming as well.