Boston Dynamics’ Cheetah Robot Uses Linear Actuators to Mimic Biology

When Boston Dynamics needed a mechanism that could perform like an actual muscle, they found the perfect solution in electric linear actuators. The ‘Cheetah’ robot – the fastest four-legged robot in all of history – is in the midst of the design process for use the military. In its current state of design, the robot can run at almost 30mph (48.2kph), but what makes it run so fast is its biological similarity to the animal it is modeled after.


DARPA (Defense Advanced Research Projects Agency), the funding source for Boston Dynamics’ Cheetah robot, has begun to model many of its robots after the animal kingdom. It is not surprising to see such a sight since much of the animal kingdom has undergone millions of years of evolution in order to create some of the most efficient, adaptive and advanced biological organisms ever seen. DARPA has stated their “goal is not to copy nature,” rather they are using nature as a base for design and technology and building from there. When an animal boasts 0-40mph in three strides, better than a Ferrari Enzo or Corvette Twin Turbo, it just may have a thing or two to teach us.


While designing the Cheetah robot, Boston Dynamics used linear actuators not only to push the legs for motion, but also to contract and stretch the spine, an essential element in the animal’s trademark stride. The motion system for the legs relies on the power of four actuators, one attached to each leg. The actuators are needed to move in very specific patterns to achieve the balance and stride, so while even at high speeds they may look synchronized, they are offset to very precise measurements.


If you look at a picture of a cheetah in the fully extended portion of its stride, you will notice that not all fours legs are touching the ground. What you will also notice is the curvature of the spine. This flexibility allows for much more speed of the animal. The Cheetah robot mimics this physical trait with two actuators comprising what would make up the spine. As the electric linear actuators pump the legs, the two spinal actuators contract and expand, bending the whole body and making it work together to optimize the speed.


Boston Dynamics has worked hard to increase the power of the robot over time. Boston Dynamics CEO Marc Raibert has stated that, “more power means faster motion and more margin in the actuators for better control.” The better the speed and control, the more versatile the robot can become.

The control system used to manipulate the motion of the spine and legs is an outboard system, but ideally will be integrated with the robot so it is completely self-sufficient. In the video, the wires that extend above the Cheetah lead to the current control system.


The Cheetah robot has been funded by DARPA in order to aid the military in defense missions, humanitarian aid and emergency response. The difficult terrain where these missions are being conducted is not always easy to traverse, and robot enables access to areas that other robots, vehicles and humans may not be able to go.


DARPA is far from finished perfecting this machine though. The Cheetah still needs to be kept in one spot by a boom-type device and can only run over flat terrain. DARPA has begun to fund the next generation of Cheetah, called the Wildcat, with the expectation of field-testing in late 2013. This robot is expected to be able to perform at speeds of up to 50mph in outdoor terrain and contain a onboard control system.


Linear actuators have many different uses that push forward some of the most advanced technology known to us today. Among those uses, the simulation of biological organisms is now added. Boston Dynamics has created a machine based on the biology of the cheetah, but with any luck will one day surpass the limits of even the animal kingdom – with the help of linear actuators.



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