See How One Team Built a Remotely-Operated Hexapod Robot Using a Raspberry Pi 4

A quick overview

This year's 2022 European Land Robot Trial (ELROB) took place in Austria and was primarily focused on trialing various robot designs in a wide range of challenging scenarios. There was a mix of civilian and military designs, with one of those being the L3X-Z that is an open source hexapod robot. The main goal for the team behind its creation was to see if their design could successfully perform in the "Reconnoitering of building structure" scenario presented at ELROB, which meant it had to navigate within a complex urban structure while simultaneously building up a 3D map of its interior and locating objects of potential interest.

Communication systems

Before the robot could be built, the team had to first plan the various methods by which the system could talk with the outside world and with itself. The hexapod uses a Raspberry Pi 4 in order to control each peripheral device over USB. It can reach the external operator by communicating over a wireless connection via its onboard MikroTik RBMetak5SHPn radio. This module provides up to 1.3W of transmission power, making it ideal for dense, concrete buildings that would otherwise block a weaker signal. Apart from this primary connection, the robot also uses the Cyphal protocol for controlling attached devices over the CAN bus.

Constructing the legs

To get the robot moving, the chassis contains a series of six powerful hip servos which each move a single leg horizontally. But rather than continuing that same method of locomotion for the rest of the joints, the leg extends by using two hydraulic cylinders. The advantage here is that classic servo motors require continuous power to hold their position, thus adding strain and shortening their lifespans, whereas hydraulics can hold a static position without power being applied. Due to the purely mechanical nature of this design, magnetic rotary encoders and their accompanying magnets were attached so that an Arduino Nano 33 IoT could read, process, and send the values to the Raspberry Pi 4 with Cyphal.

Building a virtual map

One of the most important aspects to this robot was its ability to map the surrounding environment to aid in object detection and autonomous navigation. To perform this task, a combination of a Scanse Sweep 2D lidar module and Intel RealSense camera assembly were used to gather distance data in the form of a point-cloud. Both normal color and thermal images can be captured as well through the connected OpenMV Color and OpenMV Thermal cameras that were mounted to a movable head. Finally, a radiation sensor provides the current level of local radioactivity as part of the ELROB scenario requirements.

Potential applications

Unlike more traditional wheel vehicles, a hexapod robot can climb over obstacles and maneuver with far more granularity which lends itself to more complex situations. Combined with the large number of cameras and other sensors, the L3X-Z platform is highly capable for industrial surveillance and search-and-rescue operations within hazardous locations. For more information about this project, you can read the team's write-up here on the OpenCyphal blog.