Adaptation Study of Zebro as Nano Rover for Lunar Exploration and Demonstration of Locomotion on Simulated Lunar Surface

Title: Adaptation Study of Zebro as Nano Rover for Lunar Exploration and Demonstration of Locomotion on Simulated Lunar Surface 

Author: Sharma, Kiran (TU Delft Electrical Engineering, Mathematics and Computer Science; TU Delft Microelectronics) 

Contributor: Verhoeven, C.J.M. (mentor) 

Degree granting institution: Delft University of Technology 

Programme: Electrical Engineering | Signals and Systems

Date: 2018-01-18

Abstract: The Moon is earth’s only natural satellite, it has no atmosphere, no life. The days are nearly burning,
the nights are freezing. It is old and cratered, smooth and young. Yet, curiosity and desire to explore
the uncertainty has driven man to find scientific truth. Here comes a small “Nano rover” from TU
TU Delft, Netherlands and Indian Institute of Science, Bangalore, India are working towards an
opportunity to land a space robot called “Nano Rover” on the Moon in collaboration with Indian Space
Research Organisation (ISRO), Bangalore, India. The prime objective of the mission is that the rover
should navigate on the Moon surface. The secondary objective is to capture photos intermittently
and send the data to the earth. Considering the mass and time constraints, the existing terrestrial
Zebro robot was proposed to be chosen for this purpose. However, Zebro is designed for terrestrial
applications and it has to be adapted to the extreme environment conditions on the lunar surface and
earth-moon transit orbit where the temperature can go as low as −180◦ C. Thus, it is quite challenging
to modify the existing Zebro to suite the requirements for extra-terrestrial applications. Hence, a
detailed study of lunar environment is necessary along with the extensive study on the adaptability of
Zebro to be lunar compliant. This thesis presents (i) a literature study on the environment conditions
on the Moon and during earth-moon transit orbit (ii) analysis of the existing Zebro and lists the
requirements to adapt it to be lunar compliant (iii) conduct tests on materials, components and
elements to enable usage of them for lunar and transit orbit environment (iv) design, develop and
test the On Board Computer for lunar compatible Zebro and (v) demonstrate the locomotion of the
robot on a simulated lunar terrain.
There are three major challenges in conceptualizing and realizing the Nano Rover – (i) stringent mission
management (ii) adapting it to the hostile environment such as temperature, vacuum, radiation,
vibration, shock (iii) strict product assurance needs. This thesis has comprehensively addressed these
challenges and successfully adapted the existing terrestrial Zebro as Nano Rover. Highly reliable
electronic components were chosen, tested, and used them in designing the locomotion system. A
lunar complaint On Board Computer and a motor drive system were successfully realized meeting
all the lunar mission needs. The prototype was tested successfully under extreme simulated lunar
environment conditions and locomotion on a simulated lunar terrain was successfully demonstrated.

Design of the locomotion subsystem for the Lunar Zebro: A design and implementation to ensure that Zebro can thrive on the moon

Title: Design of the locomotion subsystem for the Lunar Zebro: A design and implementation to ensure that Zebro can thrive on the moon

Author: Miog, Jeffrey (TU Delft Electrical Engineering, Mathematics and Computer Science)

Contributor: Verhoeven, Chris (mentor)

Degree granting institution: Delft University of Technology

Date: 2018-08-22

 Abstract: This report covers the development of the Locomotion system for the Lunar Zebro that is responsible for the positioning control of the six legs and the operating of the solar panel. It covers the initial problem analysis, requirement discovery, conceptual design, part identification for implementation, implementation and the first tests, their results, and the design improvement recommendations. The electronics consist of Commercial Off The Shelf Components with a short delivery time in order to meet the strict deadline. These components are not rated for their radiation performance, but test results for the operation of these components in radiated environments are publicly available. Components were selected and implemented in the design based on these test-results. The implementation of the design was tested at a radiation facility to ensure that the design meets the total radiation dose requirements.

Lunar Zebro - Software Design Of The Locomotion Sub-System With The Dezyne Model Driven Development Tool

Title: Lunar Zebro – Software Design Of The Locomotion Sub-System With The Dezyne Model Driven Development Tool

Author: Rouwen, Floris (TU Delft Electrical Engineering, Mathematics and Computer Science)

Contributor: Verhoeven, Chris (mentor); van Genderen, Arjan (graduation committee)

Degree granting institution: Delft University of Technology 

Project: The Zebro Project 

Date: 2018-08-27 

Abstract: The TU Delft ZEs-Benige RObot (Zebro) project is presented with the opportunity to bring the Zebro concept to the surface of our moon. To maximise the probability of success, the Locomotion Sub-System (LSS) software of Lunar Zebro is developed using a novel model-driven design tool called Dezyne. Dezyne uses a proprietary language to describe systems, perform model checking and execute source code generation. Dezyne is proposed for this thesis as it can improve the quality of the LSS design. This is required because the project is under strict time- and manpower constraints. The goals for this thesis are:
i. Deliver a reliable software design for the Locomotion Sub-System (LSS) of Lunar Zebro.
ii. Deliver a working implementation of the Locomotion Sub-System (LSS) software design on Lunar Zebro’s hardware.
iii. Investigate the advantages and disadvantages of the use of the model-driven software design tool Dezyne.

The current workhorse of the Zebro Project, is a Zebro called DeciZebro. Lunar Zebro builds on the legacy of the design of DeciZebro. The LSS of Lunar Zebro consists of an Locomotion
Controller (LC) and six leg modules. The requirements of the LSS software of Lunar Zebro are derived from the requirements of Lunar Zebro as a whole. These requirements are categorised according an European Space Agency (ESA) standard.

With the help of Dezyne, the system is designed, verified, simulated and integrated into native code. It is found that Dezyne is not suitable for designing the software of the leg modules.
Therefore, the LC consists primarily of generated code, while the leg modules solely contain code developed by hand.

The goals of this thesis are partly reached. An LSS software implementation is delivered with the use of Dezyne. However, the design is lacking a framework in which errors that occur
during operation can be resolved by means of extensive state machining. This is due to time constraints. Additionally, it is unclear if this specific LSS software implementation is more reliable than an implementation that is made without the use of Dezyne. The third goal, listing the advantages and disadvantages of Dezyne, is fulfilled.


Evolving State Machines as Robot Controllers

Title: Evolving State Machines as Robot Controllers 

Author: den Toom, Matthijs (TU Delft Electrical Engineering, Mathematics and Computer Science) 

Contributor: Langendoen, Koen (graduation committee), Verhoeven, Chris (mentor), Nasri Nasrabadi, Mitra (graduation committee)

Degree granting institution: Delft University of Technology

Project: Zebro project 

Date: 2019-08-23 

Abstract: Automated generation of robot controllers using an Evolutionary Algorithm(EA) has received increasing attention in the last years as it has the potentialfor a reduction in the development time of a robot. Often these EAs generateNeural Networks (NNs) as robot controllers. Using a NN for automaticallygenerating robot controllers has two important downsides: 1.) A human isnot able to fully understand the inner working of a multi-layer NN, and 2.)a NN has only limited abilities to decompose a complex task into sub tasks.Both of these downsides can be addressed by using a State Machine (SM)instead of a NN as robot controller. Therefore, this thesis introduces an EAcalled Evolving State Machines As Controllers (ESMAC). ESMAC generatesSMs instead of NNs. A SM is understandable for humans because ofits modularity and allows for task decomposition by using a state for eachsub task. Furthermore, two extensions of ESMAC are proposed: adaptiveESMAC and selector ESMAC. Adaptive ESMAC aims to automatically determinesthe number of states with which the best tness for a task canbe achieved. Selector ESMAC replaces the transitions that are used in aSM to switch between states with a NN-based switching mechanism. This switching mechanism allows mutations to make more gradual changes to aSM’s behaviours, which improves the performance of the EA. The performance of ESMAC is evaluated on two robotic tasks: come-and-go and phototaxis-with-obstacles. All three variants of ESMAC showequally good performance as a NN-based EA on the evaluated tasks. Thecontrollers generated with standard ESMAC and adaptive ESMAC hardlymake any state transitions and mainly use one state. However, controllers that do use multiple states appear to be more robust to changing scenarios and in noisy environments. Selector ESMAC is able to generate SMs-based controllers that have complementing states and, therefore, shows potentialfor decomposing a task into sub tasks.

Autonomous Exploration by Cooperative Robots

Title: Autonomous Exploration by Cooperative Robots

Author: Agrawal, Charu (TU Delft Electrical Engineering, Mathematics and Computer Science) 

Contributor: Verhoeven, C.J.M. (mentor), Epema, D.H.J. (mentor), Roos, S. (graduation committee), Mastrangeli, M. (graduation committee) 

Degree granting institution: Delft University of Technology 

Programme: Electrical Engineer | Embedded Systems 

Date: 2019-08-26

Abstract: Imagine being lost in a desert with a bunch of friends, all of a sudden. Survival will be difficult. You will have mirages, distrust among friends and no means to leave landmarks on the sand. Unable to locate yourself, you will have no means to contact people with maps. The best you can do in such a situation is to stay together in the vicinity of each other and look for food and water. By staying together, you can see more and decrease faulty data; thereby increasing your survival probability. Robots when left to explore the moon encounter the same issues. They do not have a Geo-Positioning System to locate them nor do they have a map. They have faulty sensor readings and might find it difficult to contact a human operator on earth all the time to solve issues on the moon. Since everything looks the same, there are no landmarks to memorise. As they walk around, their battery will also get exhausted. The more we equip the robot outside earth, chances of faults do not decrease, they increase. Therefore, there is a need to make primitive robots capable of autonomous exploration. We prefer sending more than one robot, inspired by the success of the collective strength of insects in harsh environments. This thesis aims at engineering collective behaviour for a group of robots in such resource-less environments like the moon. We expect this collective behaviour to perform searching in time-critical events like earthquake-stricken areas. The thesis is designed to be implemented on legged robots called Zebros. Using communication, they will collectively perform activities such that they appear as one body of tightly coupled autonomous units. We design three distinct algorithms for such missions. Emergent behaviour is expected from the robots running these algorithms. The swarm should collectively choose the best among the possible options without disintegrating into subgroups. (


Modelling the hybrid dynamics of a hexapedal robot: Predicting the Zebro's path using an identified leg-ground slippage model

Title: Modelling the hybrid dynamics of a hexapedal robot: Predicting the Zebro’s path using an identified leg-ground slippage model 

Author: Erkelens, Folkert (TU Delft Mechanical, Maritime and Materials Engineering)

Contributor: van den Boom, A.J.J. (mentor), Steur, E. (graduation committee)

Degree granting institution: Delft University of Technology

Programme: Mechanical Engineering | Systems and Control

Date: 2021-03-23

Abstract: Legged locomotion is a discrete event system (DES) due to the ever changing contact states of each leg. As such, it requires a nonlinear modelling method to predict the trajectory of a legged robot. One such robot has been focused on throughout this thesis; the six legged “Zebro”. With its half-circular legs, the Zebro is well suited for traversing uneven terrain and even climbing up small steps, making it the robot of choice for a lunar mission in the near future. A previous attempt at modelling the trajectory of a Zebro kinematically fell short when it came to modelling a curved path, with the reasoning behind this being how the Zebro’s legs can visibly be seen slipping over the ground as it walks, the effect of which is never taken into account. A combination of kinematics and dynamics was used for the model in this thesis. The reason for this is that the Zebro’s legs are actuated using position controlled motors, so the information available is the leg’s angle and the speed at which the leg is rotating, rather than the torque. Therefore, kinematics were used to estimate the vertical motion of the Zebro due to the rotational speed of each leg, which could then be used to estimate the normal contact force on each leg. The traction forces could then be estimated using the normal force and a slippage model which has been experimentally identified in collaboration with a different research team at the TU Delft. With these forces, and the Newton-Euler equations of motion, the Zebro’s path could be predicted. Applying a slippage model to a half-circular leg, rather than a wheel, required a new method of calculating the slip ratios which was based on Pacejka’s formula, but adapted to also account for the case where a leg is standing on its toe. Furthermore, a contact detection algorithm was designed to kinematically predict which leg(s) lift off of the ground during a touchdown event. This was used to kinematically model the orientation of the Zebro during a tetrapod gait and was shown to correctly predict the complicated contact transitions during said gait. Another product of the research in this thesis is a new and improved algorithm for a turning tripod gait, which achieves smoother turning than beforehand by guaranteeing a smooth contact transition between two leg groups. That being said, it cannot yet be applied to the tetrapod gait, so the current gait scheduling algorithm is still required for a turning tetrapod gait. The results of the simulations showed the Zebro walking as expected, both in a straight line and when turning, but the simulations could not be validated quantitatively due to current events regarding COVID-19. For a qualitative review of the model, photographs were taken of the Zebro during walking gaits to compare to the simulations and showed that, while straightforward walking was predicted well, the turning circle of the model was significantly sharper than in reality. The reason for this is most likely a problem in the calculation of the slip ratios, since they were consistently unrealistically low, therefore requiring further research in future.

Development of a module with driving and walking capability

Title: Development of a module with driving and walking capability: Study in the feasibility for application with a ZebRo robot

Author: Bongaardt, Laura (TU Delft Mechanical, Maritime and Materials Engineering)

Contributor: Verhoeven, C.J.M. (mentor), Babuska, R. (graduation committee), Della Santina, C. (graduation committee) 

Degree granting institution: Delft University of Technology

Programme: Mechanical Engineering | BioMechanical Design

Project: Intelligent echanical Systems 

Date: 2021-04-23 

Abstract: Robots that use legged locomotion have the ability to overcome obstacles and can negotiate a wide range of difficult terrains, such as encountered in outer-space missions. In many practical scenarios however, their applicability is still limited, mainly due to insufficient speed and efficiency. On the other hand, robots that use wheeled locomotion are fast and efficient, but are generally confined to flat or prepared surfaces. A relatively new approach, to use the advantages of both forms, is the combination of walking and driving technology into Hybrid Walker-Wheeler technology. In this research we will explore the feasibility of applying Hybrid Walker-Wheeler technology to the Zesbenige Robot (ZebRo). ZebRo is a small walking robot with six One-Degree-of-Freedom (DoF) legs and walks with an insect-inspired gait. It is being developed with the intention to go on a mission to the moon. The objective in this thesis is to increase the speed and energy efficiency of the ZebRo on flat surfaces, while maintaining its robustness and walking capability on rough terrain. We will set up the criteria for a new design, explore various options and parameters and choose a concept. We will then do a number of simulations to analyse the properties of a wheel and a leg and to apply these in the design. The final prototype consists of a single module with a wheel, a one-DoF leg and a custom-design coupling which switches torque, from the motor, between the wheel-axle and the leg-axle. This prototype was tested and evaluated on its electrical power consumption and the torque and speed transmitted to the leg-axle and wheel-axle. From these results, we were able to draw a number of conclusions and make recommendations for a ZebRo equipped with Hybrid Walker-Wheeler technology.

OPAL: A Stereo Vision Obstacle Processing ALgorithm for a Walking Lunar Rover

Title: OPAL: A Stereo Vision Obstacle Processing ALgorithm for a Walking Lunar Rover

Author: Rovers, Stijn (TU Delft Aerospace Engineering)

Contributor: Speretta, S. (mentor)  

Degree granting institution: Delft University of Technology

 Programme: Aerospace Engineering 

Date: 2021-06-30 

Abstract: The Lunar Zebro is a small six-legged robot. It has the potential to be used in a swarm carrying out objectives like exploring planetary surfaces. A new step towards autonomous navigation is made with the newly developed Obstacle Processing ALgorithm (OPAL) using primarily open-source libraries. This study showed that the initial iteration of OPAL could detect rocks and determine their absolute position to the rover’s low-positioned cameras using a stereo vision system. Obstacles and their relative distances are detected using the disparity map—the amount of shift of pixels in the stereo image pair. When translating the disparity to V-disparity, a histogram of the disparity per row, the ground and the obstacle could be isolated. It took six steps to realise this thesis goal. After setting the requirements, a test model, called Bars, was developed and tested at a location containing a Mars-like environment (Decos). This test model uses, along with Lunar Zebro’s hardware, mostly Commercial Off-The-Shelf products. With the footage, all the different components of OPAL were integrated into one algorithm. Hereafter, a pipeline on a server was created, and multiple test cases were run to establish results. The predetermined requirements of the algorithm were validated using measuring tape measurements and ground-truth bounding boxes tracked by a CSRT-algorithm. Together, Bars and the initial iteration of OPAL prove feasibility and expose opportunities and challenges, which could be a starting point for optimisations or other approaches.