SPIDAR: The Quadrupedal Robot That Can Fly, Walk With Merging Legs and Propellers

Most robots with the ability to move in different ways have limitations as they are typically made up of multiple mobility systems that do not function cohesively. For example, adding propellers to a legged robot to make it fly is feasible, but it results in the legs or the propellers being mostly cumbersome extra weight. Although some robots achieve this balance more smoothly than others, the use of multiple mobility systems is still a trade-off.

A quadrupedal robot currently in development at The University of Tokyo, known as SPIDAR, aims to address this trade-off by merging legs and propellers, which will enable it to both walk and fly. Rather than using leg actuators, the robot employs vectorable leg thrusters that can move leg joints individually and enable the robot to take off entirely.

Walking and Flying Robot

Despite having only four legs and not eight, the robot is named SPIDAR, which is an acronym for "SPherIcally vectorable and Distributed rotors assisted Air-ground amphibious quadruped Robot," though it is not designed to resemble a spider. While it does have a leggy appearance, it may provoke a similar uncomfortable reaction to that of a spider, according to IEEE Spectrum.

In general, an object can take off into the air if it has a sufficient number of thrusters. However, the real challenge lies in controlling the object and using it productively. This challenge is further compounded when the object has multiple interconnected degrees of freedom that require constant attention, as is the case with SPIDAR. It is evident that SPIDAR is currently a functional prototype, as it appears to be constantly at risk of falling apart due to its unstable nature.

Each section of SPIDAR's limbs is equipped with a spherically vectorable dual thruster that can rotate around the limb and provide thrust in any direction. Although the joints do have small servos to enable some movement, their main purpose is to simplify the dynamics of the system and operate everything onboard.

Stability Opportunities

The servos are not strong enough to support the robot's weight, and its mobility primarily depends on the thruster system. The robot has a total of eight links with 16 joints and weighs a substantial 15 kilograms, including eight batteries distributed along the links. It can fly for a maximum of 9 minutes, while its walking time is more than double that duration.

Describing SPIDAR as a "legged" robot might be too narrow in scope since the authors of the paper suggest that the limbs could be utilized for manipulation in either terrestrial or aerial environments. Moreover, significant efforts are required to make the robot a sufficiently stable platform for this purpose.

However, for the robot to be able to perform these tasks reliably, it needs to be stable. This is a significant challenge because the robot has many degrees of freedom, which means that many interconnected joints need to be controlled to keep the robot steady. The researchers are currently working to address this challenge by improving the stability of the robot, which will be essential in unlocking its full potential for manipulation in various environments.

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