Let the DLR Scout Rover Flip: Parameter Study Simulations

The DLR Scout rover is symmetrical about the horizontal plane and can drive upside down equally well as upright. The rover was designed such, because its intended area of applications, planetary caves, is very difficult to access and navigate through, tipping over is just a matter of time. Entrance through skylights or drops inside the cave can cause the rover to end upside down with a high probability. There are however reasons to prefer being upright, mainly camera and payload, but also communication, although two antennas are planned for the final design. There is thus motivation for the rover to be able to flip itself, on its own or along an obstacle, in a controlled way. In order not to put the prototype at risk and for repeatability, a simulation parameter study is performed, with a few validation points using hardware. Results show that the rover is able to flip itself on a flat plane, when the wheels abruptly turn quickly in opposite directions on both rover sides. This maneuver is currently not possible on the prototype for safety reasons. The flip simulation along an obstacle shows that a simple inclined plane is enough, with higher success rate the faster the wheels turn. Other parameters like friction or the introduction of a ditch in front of the inclined plane, have little to no impact. Driving on the side of an inclined plane to induce a roll movement into the rover, mostly is unsuccessful in simulation (sliding or ending on one side) but mostly is successful with the prototype because imperfections are enough for the rover to end upside down if it comes to rest on a side

A Modelica Library to Add Contact Dynamics and Terramechanics to Multi-Body Mechanics

The Contact Dynamics library extends the multi-body Modelica Standard Library with contact calculation to the environment, namely soft soil and hard obstacles. A focus is on terramechanics, i. e. wheels driving on soft and dry soil, and a handful of models are implemented. Additionally, a Hertz contact model for hard and elastic contact, between bodies themselves or to obstacles in the environment (e. g. rocks in the soft soil), is available as well. The capabilities of the library have been key in the development of rovers for planetary exploration such as the upcoming MMX mission to the Martian moon Phobos

TOWARDS ROBOTIC EXPLORATION OF EXTRATERRESTRIAL CAVES – THE FIRST IN-CAVE TESTS OF THE DLR SCOUT ROVER

In this work we present a test campaign of the Scout rover in a cave on Earth. Scout is focused to be as close to space-qualifiable hardware as possible in this prototype stage. We summarize planning, transport, obstacles, and campaign results

MMX Rover Simulation - Robotic Simulations for Phobos Operations

The MMX Rover, developed by CNES and DLR, will fly to and explore the surface of the Martian Moon Phobos within the JAXA Martian Moon Exploration Mission. It will be the first wheeled locomotion system in a milli-g environment. In the development of the rover, simulations have been used to test and develop its robotic activities. This paper presents the multi-physics simulations that are being used. The overall simulator setup and its main components are discussed. To provide appropriate simulations for the var-ious topics while maintaining a unified simulator, a modular approach was required. The different modules and their role will be outlined. For this, Dymola's implementation of the Mod-elica modeling language provides the basis, especially regarding multi-body dynamics, and the possibility to include external libraries, e. g. for environment interaction, control logic and visualization. Finally, examples for the simulator used in driving, uprighting, alignment and separation will be presented. These examples illustrate the approach on experiment design, setup and result evaluation. To date the MMX Rover simulator is regarded as an indispensable development and analysis tools, especially since representative lab experiments are much limited when designing a robotic system for milli-g operations. It is also planned to be used during operations phase for planning and analysis

MMX - development of a rover locomotion system for Phobos

The MMX mission (Martian Moons eXploration) is a robotic sample return mission of the JAXA (Japan Aerospace Exploration Agency), CNES (Centre National d'Etudes Spatiales ) and DLR (German Aerospace Center) for launch in 2024. The mission aims to answer the question on the origin of Phobos and Deimos which will also help to understand the material transport in the earliest period of our solar system and the most important question how was the water brought on Earth. Besides the MMX mothership (JAXA) which is responsible for sampling and sample return to Earth a small rover which is built by CNES and DLR shall land on Phobos for in-situ measurements similar to MASCOT (Mobile Asteroid Surface Scout) on Ryugu. The MMX rover is a four wheel driven autonomous system with a size of 41 cm x 37 cm x 30 cm and a weight of approx. 25 kg. Multiple science instruments and cameras are integrated in the rover body. The rover body is basically a rectangular box, attached at the sides are four legs with one wheel per leg. When the rover is detached from the mothership, the legs are folded together at the side of the rover body. When the rover has landed passively (no parachute, braking rockets) on Phobos, the legs are autonomously controlled to bring the rover in an upright orientation. One Phobos day lasts 7 earth hours, which gives for the total mission time of 3 earth months, the number of about 300 extreme temperature cycles. These cycles and the wide span of surface temperature between day and night are main design drivers for the rover. This paper gives a short overview on the MMX mission, the MMX rover and a detailed view on the development of the MMX rover locomotion subsystem

Finally! Insights into the ARCHES Lunar Planetary Exploration Analogue Campaign on Etna in summer 2022

This paper summarises the first outcomes of the space demonstration mission of the ARCHES project which could have been performed this year from 13 june until 10 july on Italy’s Mt. Etna in Sicily. After the second postponement related to COVID from the initially for 2020 planed campaign, we are now very happy to report, that the whole campaign with more than 65 participants for four weeks has been successfully conduced. In this short overview paper, we will refer to all other publication here on IAC22. This paper includes an overview of the performed 4-week campaign and the achieved mission goals and first results but also share our findings on the organisational and planning aspects

Modeling, Simulation and Optimization of the DLR Scout Rover to Enable Extraterrestrial Cave Exploration

In-situ exploration of extraterrestrial area of scientific interest, such as caves on the Moon or Mars, remains largely impossible with the state of the art wheeled rovers. One possibility to combine advantages of wheeled and legged robots is the rimless wheel. DLR's Institute of System Dynamics and Control is currently developing a modular rover with rimless wheels, called Scout. It is aimed to be capable to explore caves and other areas that are difficult to access. Development and analysis of robotic concepts at the state of the art sets high requirements on modeling and simulation, among other reasons because testing in relevant environment is only possible to a certain extent. The current trend in robotics, for space applications but also in general, aims for faster and cheaper development where digital simulation models are preferred over hardware prototypes. They're versatile and can be used as basis of optimization campaigns. Parameters and subsystems can be optimized before assembling the first prototypes. Modeling and simulation also permits to identify strengths and weaknesses early in the project. In later phases of the project and during operation, the simulations are valuable for analysis of engineering data. The modeling needs to be detailed and accurate for all this to be possible. It constantly accompanies the whole system and takes the same development steps. This work is going to detail the effort in modeling and simulation of the Scout rover as a multibody system. The whole process follows the V-shaped development process. This starts with the detailed modeling, analysis and optimization of the rimless wheels and other parts that are central to the Scout rover. Places where simplifications are valid, are shown as well. It continues with simulation tests on the full system along with optimization of parameters and subsystems. A first prototype of the Scout rover has been built 1.5 years after the start of the project. It is already exceeding the requirements and expectations. Such good results would not have been possible this fast without simulation and optimization. Refinement of the simulation model and validation against the hardware are the next steps which are currently on-going

Toolchain for a Mobile Robot Applied on the DLR Scout Rover

This paper motivates and details the tools used to control a planetary exploration rover prototype and its simulation twin. The novelty is the coupling of the prototype and the simulation. The prototype and simulation of the rover use the same software tools and code for communication, signal processing, data storage and drive control algorithms. The presented toolchain is unprecedented for mobile robot to the best of the authors' knowledge, yet generic and versatile enough that it can easily be adapted to different kinds of robotic systems as the full paper will show. Advantages and drawbacks as well as comparison to other solutions are also key content of this text. DLR's Institute of System Dynamics and Control (SR) is developing a new mobile robot called \textquotedblScout\textquotedbl that will serve as the example of the toolchain. The Scout rover is a robust cave exploration rover, based on rimless wheels and biologically inspired locomotion mechanisms. It consists of segments interconnected by elastic \textquotedblvertebrae\textquotedbl in longitudinal direction. Some of the special features of this rover design can only reasonably be unfold thanks to the toolchain, e.g. the bionic phase shift control or simulative exploration of different rover and wheel configurations. The development of the Scout rover relies on modeling, simulation and optimization and follows the \textquotedblV\textquotedbl-shaped paradigm of system development. Elements of rapid control prototyping are implemented and commercial of the shelf sensors, actuators and computation units integrated. This has rapidly led to a robust mobile robot that is capable to cross obstacles that are larger than the radius of the wheels. The Scout rover development relies on the Modelica language for guiding and safeguarding virtual design decisions as well as for rapid control prototyping using the commercial Modelica modeling and simulation environment Dymola. Using this toolchain is a good compromise for satisfying the requirements in terms of rapid control prototyping. It has effective facilities for modeling the challenging physics for reliable Model-in-the-Loop simulations, at the same time the model of the controller can be directly used on the prototype's hardware. A well-thought-out model structure allows a transparent and seamless swapping between virtual model components and model components which drive physical drives and sensors. The actuators of the prototype are addressed using the EtherCAT protocol, communication with sensors and human operators goes through a light-weight in-house middleware and logged data is stored in the popular HDF5 format. Coordination of the actuators and reaction to user input in a state machine like manner is implemented with scripts in the Lua language. Steps for further work include integration of cameras and implementation of obstacle detection, additional control algorithms and more autonomy. Operations in the field of a space mission is envisioned around 2030. The presented toolchain is thought-out enough that this won't require major changes even when COTS parts need to be replaced by space qualified hardware. Likewise, the simulation of the rover will remain an important activity

The DLR Scout Rover During The 2022 ARCHES Demomission Space On Mount Etna: Operating The Rover Outside Of Its Comfort Zone

We report about tasks, results and lessons learned of the DLR Scout rover during the ARCHES Demomission Space in 2022 on Etna. It investigated trafficability and relayed signals for an ESA rover, was platform for a haptic HMI, carried UWB transceivers and demonstrated its robustness in a survival test. Scout fulfilled all tasks and gained maturity for a space mission ~2030. Lessons were learned in thermal management, power supply and wiring, as well as operational procedures