Our project has as objective the realization of a virtual model of a quadruped rover. We started with a concept design of a terrestrial robot (designed by one of the team member) and ended up into something more suitable for planetary exploration. In order to transform the quadruped robot into a rover, it was equipped with some of most suitable instruments for planetary exploration.

Rover Model

Our quadruped rover prototype is called Rex and it is a robot with 20 joints: 3 motors (Shoulder, Leg and Foot) for each leg and a 8 DOF robotic arm.

The model is imported using an URDF file, used to assembly the multiple STL files.

Chassis, body and legs

The initial chassis design is by Deok-yeon Kim (available on Thingiverse). We edited the back part and the chassis adding holes for sensors and fixing some design issues.

We also made substantial changes in the legs. We developed a brand new leg model starting from the Open Robotic Initiative design (Max Planck Gesellschaft and New York University). Specifically, for each leg, we slightly changed their approach adding one servo motor in the shoulder (to control the leg) and other one on the chassis (to move the shoulder) obtaining a belt driven 3DOF leg.

The idea is to have a much more functional and reliable mobility for the missions that Rex has to perform.

Moreover, for the feet, we integrated a patented NASA technology: the chainmail tires. This will help Rex in overcome uneven terrains.

Robotic arm

To complete the design, we decided to add a mechanical arm, placed on top of Rex’s rack, starting from the Ergo jr (Poppy project) open source design. The arm structure has been completely revolutionized by adding 3 more DOF and replacing the gripper with the Perseverance Turret in order to equip Rex with the needed exploration tools.

Here a list of the embedded exploration tools:

• SHERLOC with the aim of studying minerals closely and detect possible signs of past microbiotic life.
• The WATSON camera that zooms in/out and records the rock and soil structures being studied from SHERLOC mineral analyzer, as well as providing an external view on Rex.
• PIXL a device able to detect the signs of past life and collect information to direct the searches.
• A drill for soil core drilling.
• GDRT a dust removal device.

Cameras and communications

In the Rex back part there are 2 Mastcam-Z and a HGA antenna for communications.

Another Mastcam-Z was embedded in the front part

All the additional tools and their design have been extracted from the resources made available by NASA as part of this challenge.

Animations as product of physical simulations

In order to build the gaits animations, we though to do not simply move the leg joints but to actually train the robot model using machine learning (specifically Reinforcement Learning). This allowed us to recreate high fidelity gaits, learned in a physical simulation (so considering masses and forces). To achieve this, we used the rex-gym open source library, owned and written by Nicola Russo (one of the team member). Thanks to this library we were able to reproduce, with a good fidelity, the environments that Rex need to navigate in the real world (e.g. setting a specific gravity force and simulating the terrains morphology).

Possible applications

One of the possible uses of Rex could be the Mars exploration. Using data from previous missions we could create a physical simulation using the NASA terrains STLs and train the rover to reach a specific point and use the tools to interact (extract/analyze) with the environment.

The idea to develop a legged device was born from the intention to make the rover able to face a wide variety of surfaces ensuring in any case a complete mobility. The ability to walk or running would allow Rex to overcome bumps, potholes and gorges and to reach hostile places.