This Robotic Fox Is a Masterclass in Mechanical Design

Broadly speaking, roboticists take one of two approaches when designing walking robots. The first approach is a kind of brute force strategy that utilizes many motors to enable the complex motion necessary for ambulation. The second approach is more elegant and takes advantage of complex mechanical linkages to achieve the same effect — though the resulting robot will be less versatile. The latter approach requires a lot more design work, as demonstrated by Will Cogley when he built this fantastic robotic fox.

This robot takes obvious inspiration from the work of Boston Dynamics, James Bruton, and others, but with a distinct twist that makes it unique. Most quadrupedal "dog" robots like this would have a motor in every joint, so they can be controlled with precision via software. That are some major benefits to that approach, but it does increase the cost, power consumption, and weight of the robot. Cogley's design is much simpler from an electronics and programming standpoint, but required far more complex mechanical design.

Each of this robot's legs is a set of two parallel linkages: the first parallel linkage connects the hip to the knee, and the second linkage connects the knee to the top of the ankle. The linkages are interconnected, so the positions of the hip joints affect the knee and the ankle. Both of those top two hip joints are actuated by servo motors through gears. The coordination of the motor positions moves the entire leg, as well as the angles of the knee and ankle. In addition, each leg has another servo before the hip joint that lets the leg pivot inwards or outwards.

Cogley designed the entire robot within Autodesk Fusion 360. Before becoming a writer, I was a mechanical designer and CAD was my entire job. So I can say with confidence that Cogley's design work is impressive—this robot's leg mechanisms were not easy to devise or execute. Every mechanical part was designed for Cogley to fabricate on a Prusa Mini 3D printer, with a minimal number of bearings and fasteners.

For the time being, Cogley is using a servo motor tester to control the robot. That's a temporary solution to help Cogley test the prototype robotic fox and refine the movement. In the future, he'll be able to move to a dedicated controller that can mount to the robot itself.