Weighing just 9kg, the quadruped reportedly has “a range of motion that rivals a champion gymnast” thanks to limbs that bend and swing to either side, letting it walk right-side up or upside down. It “trots” over uneven terrain at 8km/h, about twice as fast as the average person’s walking speed, and its creators claim it could be tuned to go twice as fast. When kicked to the ground, it quickly rights itself with a “swift, kung-fu-like swing of its elbows” – and, of course, it can do a complete backflip from a standing position.
Developed by a team led by Benjamin Katz in the Massachusetts Institute of Technology department of mechanical engineering, the Mini Cheetah has capabilities similar to robots from Boston Dynamics. It also has a key difference that could make it appealing to AI researchers around the world, however – low-cost components.
“Boston Dynamics is commercial, expensive – if you break it, it’s going to cost you a lot. These guys claim to be cheap and accessible,” said Imperial College London research associate Dr Ali Shafti to Professional Engineering. “I think that is what they will actually contribute to robotics research. It provides a good sandbox, a good playground for other researchers who don’t want to build from scratch.”
Each of the Mini Cheetah’s limbs is powered by three electric motors that researchers engineered using off-the-shelf parts normally used in drones or remote-controlled aeroplanes. The motors are easily replaceable, and parts are designed to be swapped for new ones, “like Lego”.
“A big part of why we built this robot is that it makes it so easy to experiment and just try crazy things, because the robot is super-robust and doesn’t break easily – and, if it does break, it’s easy and not very expensive to fix,” said Katz.
Flipping amazing
A key part of the robot’s design is its agility and nimble movement. MIT said its lightweight, high-torque, low-inertia design “enables the robot to execute fast, dynamic manoeuvres and make high-force impacts on the ground without breaking gearboxes or limbs”.
Its “feet” touch the ground for about 0.15s at a time, during which a computer tells it to increase the force on the foot, then change it to balance, and then decrease that force very quickly to lift it up.
Amazingly, the Mini Cheetah reportedly achieved the first ever backflip from a quadruped robot on its first attempt. “We thought it would be a good test of robot performance because it takes a lot of power, torque, and there are huge impacts at the end of a flip,” said Katz.
The MIT announcement said the team wrote “’giant, non-linear, offline trajectory optimisations' that incorporated the robot’s dynamics and actuator capabilities, and specified a trajectory in which the robot would start out in a certain, right-side-up orientation, and end up flipped 360 degrees. The program they developed then solved all the torques that needed to be applied to each joint, from each individual motor, and at every time period between start and end, in order to carry out the backflip."
Robo-races
Even if the Mini Cheetah fails to complete a flip, the researchers said it is designed to be “virtually indestructible,” recovering with little damage. “It is a good prototype to be playing with and harder to break apart… lower-cost, easy-to-buy components make it a nice platform to build on,” said Shafti, who was not involved with the research. Computer scientists and control engineers need mechanical platforms to test AI programs, he said, and the Mini Cheetah could be a promising testbed.
“Particular applications that come to mind are mainly in hostile environments where there is a risk for humans to go into… because of the four-legged structure it has, and mechanical compliance it has, it can handle different types of terrain easily.” Promising applications for nimble, autonomous quadrupeds could include search-and-rescue missions or environment mapping.
The MIT team is now working on a landing controller – “I want to be able to pick up the robot and toss it, and just have it land on its feet,” said Katz, “throw the robot into the window of a building and have it go explore inside” – and making more of the machines. They aim to build 10, which would be loaned to other laboratories.
The engineers eventually hope to run Mini Cheetah races, pitting other researchers’ AI capabilities against each other – a spectacle that could make a simple backflip seem quaintly archaic.
Content published by Professional Engineering does not necessarily represent the views of the Institution of Mechanical Engineers.