PRE2020 4 Group2

Group members

Name	Student ID
Jasmijn de Joode	1358073
Robin Foppen	1394746
Mirre Bosma	1266489
Dirk de Leeuw	1358081
Job van Heumen	1380036

Problem statement

Natural disasters, war, terrorism or other causes, can cause structures to collapse in urban areas. When this happens, Urban Search and Rescue (USAR) will be deployed to search for and rescue the victims trapped by these structural collapses. There are certain steps to be taken when a building collapses: one of them is to analyze the building for safety hazards. A very dangerous hazard is fires and explosions, which can be caused by gas leaks. It is important that this analyzation of the building is done as fast as possible, since the chances of survival are highest when people are rescued within 72 hours . After this time frame, the number of survivors found drops drastically. Robots might be able to help meet this 72 hour deadline, by going into the building before it is safe enough for the search and rescue workers to go inside of the rubble and analyze the building for possible gas leaks.

Deliverables

There are different kinds of Urban Search and Rescue robots, but we will focus on one kind in particular: RoboBees. RoboBees using a particle swarm optimization algorithm may be able to help to find gas leaks in collapsed structures and thus prevent explosions and help meet the 72 hour deadline without diminishing the safety of the search and rescue workers. To use this algorithm, the RoboBees have to be able to communicate with each other and with the USAR team. For this project, we will do research on the communication needed between RoboBees and the USAR team to be able to use a particle swarm optimization algorithm for detecting gas leaks in collapsed buildings. We will also discuss the particle swarm optimization algorithm itself and the societal relevance, limitations and possible future improvements of using RoboBees for detecting gas leaks.

USE

User

The target group we're focusing on can be defined as the rescuers that are operating within these collapsed buildings. As mentioned in the problem statement, the USAR department is dealing with this specific problem of gas leaks and their consequences. Therefore they will make use of the RoboBees to detect any gas leaks. The use of Robobees can be extended to other departments when needed in the future. Besides the detection and contribution to the 72-hour deadline, will the rescuers benefit from the fact that the RoboBees will enter the building in their place. Buildings need to be safe from any hazards before any human being can enter them, by sending robots the danger will decrease for the USAR department itself.

Society

Society will benefit from these robots since the time needed to inspect the building will be reduced. This will influence the time the rescuers will start to look for victims and rescue them. The chances of surviving are negatively correlated with the duration of being stuck in the building for example. This will affect the directly related victims present in the building and the neighborhood will benefit from this efficiency. The earlier the location of a gas leak is detected, the more they can prevent and avoid any consequences.

Enterprise

The enterprises involved in this specific problem will manufacture the materials and the development of the RoboBees. Thereafter they will be bought by the government since the USAR or fire department will be using the RoboBees to detect gas leaks within collapsed buildings.

Week planning

Week	To do
1	First lecture and think about possible subjects
2	Do research about chosen subject
3	Do research about specific rescue robots and specify subject.
	Research what needs to be done in case of building collapse. Look into what needs to be done in order to be able to enter a building safely.
4	What does the robot need for specific techniques? Look into what techniques already exist and what is still needed.
5	Research communication between RoboBees and look at limitations/problems
6	Design prototype. Discuss the prototype and what possible future improvements are
7	Extra time to finish the prototype or solve other unforeseen problems. Make the presentation
8	Record presentation
9	Clean up wiki

Abstract

There is already so much possible and so much knowledge about robots and how they can help make our lives easier. Even if we limit ourselves to rescue robots, there exist too many robots to know them all. So, at the start of this project we wanted to do an assessment of the different robots that already exist and can assist in search and rescue missions. This way we can get a feeling of what already exists, what is still missing and what is possible nowadays. An overview of different kinds of robots is described in the chapter about the state of the art.

Next, we needed to limit ourselves even more than just saying rescue robots. So, in order to choose a specific direction we looked at what needs to happen in the case of a collapsed building. After looking at the different steps that need to be taken in a search and rescue mission, we decided that to look into robots that can assess the risks when entering a building after it has collapsed. These risks include gas leaks, electric shock, partial collapse and asphyxiation hazards.

After looking at the multiple ways that robots can help detect and/or solve safety risks, we have chosen to look into how robots can help with the detection of gas leaks. The current idea is to investigate robot swarms. This means that you take at least 3 robots. These robots must carry equipment to detect different kinds of gasses and they communicate with each other to find the spot with the highest amount of gasses in the air.

State of the art

In this section we look at examples of the newest/best-developed robots that exist at this time. The different robots have been divided into ground robots and aerial robots. The ground robots are then again split up into legged robots and tracked and wheeled robots. There are also robot competitions. What is the value of this?

We will discuss the state of the art of Search and Rescue (SAR) robots. There are two types of SAR robots, namely Urban Search and Rescue and Maritime Search and Rescue. We will only focus on Urban Search and Rescue (USAR). USAR may be needed for multiple kinds of emergencies, for example earthquakes, storms and tornadoes, floods and technological accidents. Research and projects are concerned with localizing, extracting and medical stabilization of trapped victims.

Since disaster areas are often dangerous for humans, it is convenient to make use of robots to investigate the area and help victims. Robots are also capable to carry out tasks which are very hard or even impossible for human rescue teams, for example finding victims with the help of thermographic cameras.

Current applications of USAR robots do not include autonomous robots. This is because current technology is not advanced enough to develop fully autonomous robots which are capable to cope with these complex, unpredictable and unstructured environments. Maybe in the far future there will be autonomous robots which can execute USAR missions without any help of humans. However, this is not realistic on short term. This does not mean that robots are not helpful in current USAR projects and missions, but we need to find a balance in the human-robot interaction. There are different kinds of USAR robots, we will discuss ground and aerial robots.

Ground robots

One of the primary challenges for ground robots is the movement in the environment. This is a hard task, because in contrast with for example traffic environments, disaster areas are often unstructured, unpredictable and unknown. It usually also contains many obstacles. To avoid these obstacles, USAR teams can make use of legged ground robots.

Legged robots

Legged robots are robots with jointed limbs, that often imitate legged animals. They can assist a rescue team with carrying heavy payloads, are able to perform long-duration missions, and are able to interact with the environment and to move in complex terrains. For search and rescue, they should be able to apply different gaits and maneuvers depending on the terrain and obstacles..

ANYmal.

ANYmal

ANYmal is developed to be deployed on the field and work in harsh conditions. It has incorporated laser sensors and cameras, so the robot can perceive its environment, accurately localize and autonomously plan its navigation path and get there by carefully selecting footholds while walking. It only weighs about 30 kg, so the robot can be easily transported by a single operator. Researchers are still further improving the locomotion skills of ANYmal to make it capable of dealing with situations that might be encountered in a search and rescue scenario and they will integrate an arm on ANYmal: this will result in the robot having the potential to manipulate objects, to move through closed doors, or simply to use the arm as an additional point of contact.

KROCK-2.

KROCK-2

Krock-2 is, like ANYmal, a quadruped rescue robot with sensors and subsystems to make it suitable for disaster response missions. The robot has force sensors with which the robot can feel its immediate environment, and thus improve its locomotion capabilities. It can surpass obstacles twice as high as the robot itself but also move under narrow passages of the same height. The components of the robot can be replaced easily on the field. Next to that, the robot is mechanically symmetrical from top to bottom, front to back and left to right, which results in the robot being able to operate in any condition even after a fall.

Atlas

Atlas

Atlas, unlike the other legged robots mentioned here, is more human than animal like and walks on two legs instead of four. Atlas is intended to aid emergency services in search and rescue operations: this includes performing tasks such as shutting off valves, opening doors and operating powered equipment in environments where humans could not survive. It is able to walk over a wide range of terrain, like snow, and can do backflips and cartwheels. It uses sensors to remain balanced, avoid obstacles, assess the terrain, help with navigation, and manipulate (moving) objects. In the 2015 DARPA competition of robotics, Atlas was able to complete all eight tasks as follows: drive a utility vehicle at the site; travel dismounted across rubble; remove debris blocking an entryway; open a door and enter a building; climb an industrial ladder and traverse an industrial walkway; use a tool to break through a concrete panel; locate and close a valve near a leaking pipe; connect a fire hose to a standpipe and turn on a valve.

BigDog.

BigDog

Another quadruped robot is BigDog, which is not created particularly for rescue, but for military use. It was created in the hope it would be able to serve as a robotic pack mule to accompany soldiers in rough terrains, instead of conventional vehicles: because instead of wheels or treads, BigDog has four legs, allowing it to move across surfaces that are too rough for wheels. BigDog uses a variety of sensors, including joint position and ground contact. BigDog also features a laser gyroscope and a stereo vision system. It can travel on several kinds of terrain, like ice, mud, forest and it is able to recover balance after skidding in slope or when kicked by someone. By the hand of this robot, Boston Dynamics has developed more quadruped robots like WildCat (which was the fastest untethered quadruped robot in the world in 2013), LittleDog, and Spot.

MIT Cheetah.

MIT Cheetah

Another quadruple-legged robot is MIT Cheetah: the total power utilized by the robot is very much similar to running animals. The robot has good locomotion skills, it can for instance run on a treadmill and on grassy and uneven terrain in a controlled manner and jump over hurdles.

Why (four-)legged robots?

Legged robots have more potential than wheeled or and tracked robots because they can work in cluttered terrain, complex and hazardous environments, since they are more like humans and animals. The quadruped robots are the best choice among all legged robots related to mobility and stability of locomotion, because four legs are easily controlled, designed, and maintained compared to two or six legs. However, legged robots in general are hard to control. These robots need to have complicated structures with multiple legs and actuators for stability and multiple sensors to perceive their environment. This results in that the legged robots are often more expensive than wheeled or tracked robots. This is one of the reasons that legged robots are currently not used as much as wheeled or tracked robots in real-life situations. Another technical problem is that legged robots in a disaster environment need to be very adaptable, not just in their intended design, but they also need to be able to adapt to possible damage, for example to the loss of one of its legs. This is important, because legged robots are usually more fragile than wheeled or tracked robots. Learning algorithms can be used to solve this problem.

Tracked and Wheeled robots

One of the largest problems with Rescue robots is mobility. Many robots already in use outside of USAR can only move on certain terrain types mostly on flat surfaces. But in USAR this is not always an option. So for wheeled and tracked robots we need options that allow us to traverse difficult terrain. A few options of The wheeled and tracked robots are:

The triSTAR locomotion unit - This robot consists of base with 4 wheels. But to overcome the mobility problem it has special wheels. These wheels are actually three wheels that turn individually and if an obstacle is met these three can turn around each other to climb the rubble. This topic has been researched already and i do not think that many more advances can be made on this robot.

CMU modular snake - A second option would be the CMU modular snake. These Robots consists of smaller parts that can move independently from each other. THis allows this robot to move through difficult terrain. This robot can still be developed further and may be interesting to look at. We also have more types of modular snake robots like the kulko, PIKo and Omnithread robots.

Stanfords snake robot- This robot works by extending from the tip. This allows the robot to travel through loose sand and small holes and even spikes. Since this robot is still in development many advances can be made.

Aerial Robots

Unmanned Aerial Vehicles (UAV’s) have many benefits over ground vehicles. They can be used to get a good view on the disaster area, but they can also be used to get to small spaces where UGV’s cannot reach. However UAV’s also have some disadvantages. Because of their size and power constraints, UAV’s are not able to carry heavy equipment or medical supplies with them. Furthermore, they are usually quite fragile. This means that UAV’s need to be very careful to not collide into walls or other obstacles.

When a building collapse, the first hours are the most crucial. The search and rescue is extremely time-consuming and difficult at the same time. The main reason what makes it this hard, is because it is simply too dangerous to just enter. In these cases, a tunnel needs to be constructed or the building needs to be entered from the top . The presence of living victims demands the available resources on those structures. Unmanned aerial vehicles can provide a solution to this time-consuming problem . UAV’s are capable of entering small spaces and search through structures that are too dangerous for the rescuers to enter. These small vehicles can pinpoint the exact location of the victims within the collapsed building, and potentially detect the assessment of the victims’ condition. When using UAV’s in collapsed building search mission, a highly specialized equipment is needed. The following list shows the must haves for such a mission and some considerations. Note that most of the features add some weight or require power, only limited supply available!, can affect the endurance of the UAV.

Four type of drones: 1. Multi-rotor: best option for usar! 2. Fixed wing 3. Single roto 4. Hybrid vtol

Contests

ICARUS

ICARUS focuses on developing integrated tools for search and rescue, utilizing teams of air, ground, and marine vehicles. One of the projects of ICARUS is an unmanned ground vehicle (UGV) which consists of two UGV’s: One large UGV and one small UGV. The larger UGV is used as a Mobile sensor platform. The large UGV collects large amounts of data that is necessary to navigate through the environment. Platform for powerful manipulator. The large UGV will be able to remove small obstacles from its path or to free a victim. Transport platform for small UGV. The large UGV will be used as a platform to carry several small UGV’s. The small UGV is used to enter collapsed buildings without damaging these buildings. These small UGV’s can be used to find and help trapped or injured victims. Since this vehicle is small it cannot be equipped with sophisticated sensors nor with a powerful computation unit. For this reason, the level of autonomy of this vehicle will be quite low.

TRADR.

TRADR

After the earthquake in Amatrice, Italy in 2016, a team of the TRADR project made use of two UGV’s and three unmanned aerial vehicles (UAV’s) (see the picture on the right) to provide a 3D model of two partially collapsed churches. The mission was a success and the UGV’s and UAV’s were able to collect enough data for a high quality 3D model of the two churches.

Taurob tracker.

Technological development

Natural disaster scenarios are one of the reasons why ground robots are being developed. One of the main challenges is to be able to navigate on complex terrain. Another reason that pushes the technological development of tracked and wheeled robots are open robotic challenges. Some examples are: The ARGOS challenge (ARGOS, 2017). This challenge was won by team argonauts with a tracked robot from the company TAUROB (TAUROB, 2017) (see Figure 3). The DARPA Robotic Challenge. After the nuclear disaster at Fukushima in Japan 2011 it became clear that humans are very vulnerable to natural and man-made disasters. Existing rescue robots were at that time unable to prevent or reduce the damage. This was the reason that the Challenge was created in 2012 by the Defense Advanced Research Projects Agency (DARPA). The primary goal of the challenge was to stimulate the development of human-supervised ground robots which should be able to execute complex tasks in dangerous environments.

What to do in case of a structural collapse?

As the title pretty much already tells us, this section is about what to do in the case of a collapsed building. We already saw that in a rescue mission, the first 72 hours are the most important for rescuing survivors. In this section we will see what needs to be done to act as safely and efficiently as possible.

There are multiple sources that give a 5 step plan in case of a collapsed building. Although they differ slightly, they all boil down to the same 5 steps. We will use the steps set by the OCHA

• The first step is initializing the search and rescue teams as quickly as possible.
• The second step is analysis of the building. What are the dangers for rescue workers when entering the building?
• The third step is finding the survivors in the building.
• The fourth step is getting people out of the rubble.
• And the fifth and last step deciding when to close the operation.

Step 1 - initializing search and rescue teams

On the site of USAR, it says that they are available in the Netherlands within 4 hours and internationally they can be on-site within 24 hours. As we saw in the problem statement, it is very important for search and rescue teams to be on-site and working as quickly as possible, since the first 72 hours are the most important in recovering survivors.

Step 2 - analyse the building

The book Protecting Emergency Responders, Volume 4: Personal Protective Equipment Guidelines for Structural Collapse Events gives a great overview of the different dangers there are in a search and rescue mission. So, we will use this book to give a short summary of the different kinds of hazards. They make the differentiation between physical, chemical and biological hazards. These three hazards are in turn divided into sub hazards. So, we will look at these separately, since they all need different approaches to dealing with them.

Physical hazards

Falling objects and collapsing structures

Electric shock- After a collapse, electric cables can be downed and severed. Rescue workers and people who were in the building at the moment of the collapse can get hurt from this in several ways. Rescue workers can get hurt from direct contact with an electrical source, but electricity can also reach a rescue worker through the air. Possibly clothing can catch fire because of heat generated by an electric source. And of course, if there is flooding, electricity could also travel through the water. Basically, there are many ways in which severed wires can hurt rescue workers. So, it is very important to make sure that electric lines are not energized.

Fires and explosions - There might be fuel stored on-site or be gas leaks that provide fuel for fires or explosions. an explosion could have been the cause of the collapse in the first place, or maybe pipes have burst because of the collapse. In either case, it is important to check. Especially, since electric cables might be severed, they can easily spark a fire. Also, the collapse might be the result of a terrorist attack. In this case, there might for example still be bombs that could go off.

Hearing loss because of excessive noise - The site of a collapsed structure is very noisy. For example, in order to free people from the rubble, excavating equipment is needed. These tools for drilling and digging make a lot of noise.

Asphyxiation hazard - There are a number of reasons why there might not be enough oxygen in a certain space. There can be oxygen consumption or oxygen displacement. Oxygen consumption can happen when there is combustion in a poorly ventilated space or if there are a lot of people in a small space. Oxygen displacement can occur when large amounts of gasses are released into a (small) space.

Chemical hazards

There are numerous chemicals that can be released due to the collapse of a building. The chemicals can come out of the building materials that are pulverized or chemical storage tanks or containers can be damaged because of the collapse. If there is incomplete combustion or fires, this can increase the amount of chemicals in the air.

Biological hazards

The last hazard to discuss is biological hazards. Possible ways for pathogens to be released are from damaged sewer systems or they can be bloodborne from infected patients.

Step 3 - find survivors

This step has been most researched in combination with robot assistance. On multiple occasions, robots have helped find people caught in the rubble.

Here we will mainly look at ways where no robots are used.

Rescue dogs - The use of rescue dogs is very important. The exceptional nose of dogs can help the rescue workers locate victims. One of the downsides of using dogs is the communication between the dog and its handler. This lack of communication might lead to incomplete or inaccurate information, which in turn could mean missing someone. . Another problem is that dogs might get to a location where rescue workers are not (yet) able to get. This is why research has already been done as to how robots might assist canine search.

Knowledge of locals - Locals might know where in the building the chances are the biggest that people were there at the time of the collapse.

Weak buidings - Weak buildings can of course collapse very easily, but the material is often also very light. Which means that the chance of people surviving even though they are covered under the building, is higher than when a building is made of very heavy material.

Strong buildings - Certain parts of buildings are stronger than other parts. Under/in parts that are very strong, the chances are largest that there are open spaces where people are caught in. So, if people were inside these spaces at the time of the collapse, the possibility of survival is quite high.

Video cameras - Using cameras with heat vision, the hot spots on the video might be identified as people.

Listening - This is a powerful tool as people who cannot move but are still conscious might be shouting to get people to hear and locate them.

Shifting rubble - When lifting debris, limbs of survivors can become visible.

Step 4 - rescue survivors

Once the hazards of going into the building have been identified and it is known where survivors are located, the next step is to rescue the survivors. The only way to do this is by creating pathways through which the victims can be reached and help them get out.

Step 5 - close the operation

At some point, the chances of finding survivors has become so low, that the operation can be closed. But deciding when this is, is always a difficult decision to make.

Next step

For the remainder of this project we will look at how robots can help in the second step - analysis of the building. For the first and last two steps, people are needed. At least for the foreseeable future, our technology is not advanced enough for robots to do this on their own or be of significant help in these steps. For step 4 - finding survivors - a lot of options already exist, such as infra red video search and robots that can assist dogs. So, we think that there is room for improvement for robots that can help survey the building to make sure rescue workers can enter the collapsed building safely.

RoboBees

After we had done research about USAR robots in general, we found out that we needed a more specific and clear problem statement. We already discussed some possible problems statements, for example:

• How can robots help or free trapped victims?
• How can robots stabilize buildings after a disaster?
• How to find out whether a building is safe enough to enter?
• How to find or even stop possible gas leaks?

After some discussion, we decided to focus on the problem of finding gas leaks. We think that this is a specific and clear problem. After this, we tried to find out which robots would be best suited for this task. It is important that the robot is able to deal with complex terrain and can enter small spaces. We considered the following options:

• Wheeled or tracked robots. Wheeled and tracked robots are usually not very good at dealing with complex terrain and obstacles compared to legged robots and aerial robots. They are often also quite large. Therefore, they are probably not the best option to deal with this problem.
• Legged robots. One advantage of legged robots is that they are well suited for passing through harsh terrain. This is very useful because after a disaster the terrain can be very uneven and can contain many obstacles. Legged robots also have some disadvantages. They are, just as wheeled and tracked robots, usually quite large, so they are unable to enter small spaces. It is also a hard technological challenge to develop a well-functioning legged robot. So currently legged robots may not be the best option for this problem.
• Aerial robots. Aerial robots are compared to ground robots easier to navigate through complex terrain. They are also well suited for entering narrow spaces. A disadvantage of aerial robots is that they cannot lift heavy equipment. This also means that they cannot carry a large battery and therefore they have to recharge faster than ground robots. However, we think that the advantages, in this case, outweigh the disadvantages and therefore we think that small aerial robots are the best option for dealing with this problem.

So in the end we choose to do some research on aerial robots and we found the so-called RoboBees.

What are RoboBees?

RoboBees are flying microrobots. They are developed by researchers at the Wyss institute (a research institute at Harvard University) and researchers at the Harvard School of Engineering and Applied Sciences (SEAS). The Wyss institute develops new engineering innovations which are inspired by nature. They use the term biologically inspired engineering for this. One of the innovations of the institute are the RoboBees. The RoboBees are inspired by insects, in particular bees and flies. The researchers try to understand the biology of flies, because flies are very good at maneuvering through the air even though they have tiny brains. Besides their use in search and rescue missions, RoboBees can also be used for crop pollination, surveillance, as well as high-resolution weather, climate, and environmental monitoring.

Main components

The RoboBee development can be divided into three main components :

• The body. Body development consists of constructing robotic insects able to fly on their own.
• The brain. Brain development is concerned with “seeing” the environment with the help of sensors and reacting to it.
• The Colony. The Colony’s focus is about using the RoboBees to work together as a swarm.

The body

The body frame of the RoboBees is made out of carbon fiber, this is a very strong and lightweight material. The joints are made out of plastic. To construct these RoboBees, researchers at the Wyss Institute have developed innovative manufacturing methods, so-called Pop-Up microelectromechanical (MEMs) technologies. This is a technique inspired by origami. The wings of the robot flap at 120 times per second using piezoelectric actuators. These are strips of ceramic which can expand and contract with the use of an electric field . Researcher are also developing a version of the RoboBee which is made out of soft material, this makes it more flexible and less fragile .

The RoboBees are already able to do a controlled flight . This means that they are able to hover and steer with the help of a power cord. Currently, researchers are working on the development of RoboBees which are able to fly without the help of an external energy source. This is a hard challenge, because at small scales flight is quite inefficient – it costs relatively a lot of power. However, researchers already developed a RoboBee which can fly without power cord inside the lab . This version of the RoboBee had extremely lightweight power circuits, and high efficiency solar cells on board. The RoboBee needed the solar power of about three Earth suns to fly. The researchers simulated that level of sunlight in the lab with halogen lights. So, currently RoboBees are not far enough developed that they can do a solo flight outdoors without external power source, let alone with equipment like GPS and gas detection on board. The researchers will continue to develop the RoboBee until the RoboBee is able to do a solo flight outside. Since the RoboBees are very small - which makes flying quite inefficient - Harvard roboticists have to come up with solutions to save energy. They developed a version of the RoboBee which was able to stick to surfaces . This was inspired by animals like bats, birds or butterflies. The team made use of electrostatic adhesion, this is the same principle that causes a negatively charged balloon to stick to a positively charged wall. This method is about 1000 times more energy efficient compared to hovering.

The brain

Once the microrobot is able to fly without an external power source, the next step is onboard control. This means that the robot is able to “see” and react to the environment with the help of sensors. This is currently not possible, because the RoboBees cannot carry heavy sensors with them on the flight. Besides this problem, developing a robot that is able to fly on its own is hard challenge, this is the case because small changes in airflow can have a big effect on its movement. Therefore the control system of the microrobot must be able to quickly react to these external forces in order to keep the robot stable. This means that the control system has to be lightweight, small and computationally efficient. Currently, control is still wired in from a separate computer, though a research team is working on a computationally efficient brain that can be placed on the robot’s body. .

The Colony

The Wyss institute is already working on programmable robot swarms. However, they are not able yet to implement it in the RoboBees. This is because the RoboBees are currently not far enough advanced - they cannot carry enough equipment with them to operate as a swarm. However, the research team at the Wyss institute developed a simple low-cost robot called “Kilobot” which is an easy to use robotic system . With these robots the researchers are able to test collective behavior and advance the development of robot swarms. For example, the researchers already developed an algorithm which allows the Kilobot robot swarm to form into any desired shape.

Swarm Technology

Communication

One of the most important requirements of the robobees is the ability of communication between the robots and between the robots and the USAR team. This is because communication plays an important role in the collective perception of the swarm. Collective perception combines the data the individual robots in the swarm have collected into a bigger picture. This allows the individual robots to make decisions as a swarm and eventually in our case find the source of a possible gas leak. There are different options for communication between the Robobees, and certain requirements to look at. On the one hand we need a fast, reliable and large enough way to communicate and on the other hand we need the Robobees to be able to fly. When we look at different communication methods, we have: physical connection, bluetooth, a LAN either using ethernet or WiFi, or another way to communicate using the environment.

Communication methods

Physical connection

A physical connection means that the different robobees are connected by wires. It does not take long to see that this way of communicating between the robots is impractical. The wires could get in the way when trying to travers difficult terrain and are too heavy to keep the robots flying.

Bluetooth

A more promising way of communicating would be Bluetooth. Bluetooth consists of four classes. Class 1 is used for long range with a maximum range of approximately 100 meters. Class 2 is the most promising at a range of about 10 meters.(2) The higher classes have a range of less than a meter which could be too small for our purposes. The range of all these classes are reduced by objects that stand in the way. Class 2 would probably be the best option for communication between the robobees. When looking at the weight of the class 2 bluetooth transmitter and receiver we get an average of 20 grams which is light enough to be put on the robobees. A small problem with these bluetooth transmitters is that when the source of the gas leak has been found, it could be difficult to transmit this to the USAR workers.

LAN connection

LAN has two different ways to connect. Firstly, we have ethernet which needs a physical connection, so this would not be ideal for Robobees. Secondly, there is WiFi, which needs larger transmitters and receivers to work than a Bluetooth connection, which would add to the weight of the Robobees. However, WiFi could work better for longer distances.

In conclusion, for communication between the Robobees the easiest solution would be to transmit between the robots at a Bluetooth class 2 connection. If there is a possibility of a “Queen bee”, a wifi connection or a class 1 Bluetooth connection could be used to transmit the data to the USAR team.

Networks

Considering that the Robobees are UAV drones, a swarm of Robobees can be seen as a wireless mesh network. A mesh network is a network topology, where each node communicates data for the network: meaning that all nodes cooperate in the distribution of data in the network. There are two techniques that can be used when designing a mesh network: a routing technique or a flooding technique.

Routing technique

With a routing technique, the message is propagated along a path. The message goes from node to node until the destination is reached. To ensure the path is not compromised, the network must use self-healing algorithms to ensure continuous connections between nodes and reconfiguration around broken or blocked paths. This ensures that a routing network is often reliable, because there are more than one paths to use to communicate a message between source and destination.

Flooding Technique

When using a Flooding technique, the message is sent to all the nodes in the network instead of using one specific route to send the message from node to node. This is a highly reliable technique, since there is no routing and thus the route cannot be compromised. There are no self-healing algorithms needed. Next to that, flooding also has the advantage that because signals arrive at each node, the blocking of one or even more paths has little consequences. This results in the maximization of the robustness of the network handling obstructions, interferences and resistance to multipath fading. Also, minimal computing power and memory is needed because there is no routing. This means low power consumption, low PCB estate and low cost. There are however still some challenges regarding the flooding technique. For instance, “broadcast storms” (data packet collisions), the efficiency of propagating the message towards its destination, and ending the process without an energy-wasting avalanche. Using a synchronised-Flooding approach with a synergic combination of techniques can fortunately solve most challenges.

Design considerations

When a wireless connection is used to communicate a message between the nodes, there are some restrictions that may interfere with a reliable and continuous communication between the nodes. The main design considerations to look at when using a wireless network compared to using a wired network are: bandwidth of the links connecting the nodes, computing power and energy supply.

Energy consumption

When using a routing based network, the number of nodes operating is always lower than using a flooding based network (since the message is conveyed not to all nodes but from one node to another node at a time). This means that a routing based network consumes less energy. However, in modern flooding based networks, less power can be used to achieve the same range since the energy of the signals received from adjacent nodes adds up. For routing techniques, smaller networks consume less energy and for Flooding techniques, larger networks consume less energy (or when the average size of the message is small).

Range

For routing techniques, the range is highly affected by the physical layer and the software of the network. Flooding techniques have a better range since the nodes sum up the energy from all the received nodes.

Latency

Latency is not that important in the case of gas leaks, because the timing of the reading is not a deciding factor in the danger of a gas leak. For instance in avoiding a collision, then the time for relaying a message is of high importance because it is a deciding factor in whether the collision will take place or not. In general, routing based networks have higher latency than flooding based networks.

Algorithms

Particle Swarm Optimization

The idea behind using robot swarms in detecting gas leaks is that a gas leak emits gasses and the closer you are to the gas leak, the higher the concentration of gasses is. So, if you find the location in the space where the concentration gas is highest, then you have found the gas leak. One approach of finding a maximum within a certain space is called Particle Swarm Optimization (PSO). PSO uses multiple entities that communicate and cooperate with each other in order to find a maximum. Each entity keeps track of three 3-dimensional vectors:

• The location where the entity currently is (called x_i)
• The location where the entity has found the highest value so far (called p_i)
• The value of p_i (called pbest_i)
• The velocity of the entity (v_i)

Here, the i represents the entity. Each iteration, the value of the current location is measured and evaluated. If the value of the current location is higher than pbest_i, then p_i is updated to represent the current location and pbest_i takes the value at p_i. If the value of the current location is lower than pbest_i, then p_i and pbest_i remain the same. At the end of each iteration, the velocity of the entity is updated. The next value of v_i, depends on its current value, the personal best location of the entity (p_i), the overall best location of all the entities and it is partly random.

The way PSO can be used in gas detection is by taking multiple robots and letting these robots be the entities in the PSO model. Every robot carries a gas detection unit and the concentrations that this unit measured can be used as the values for the PSO model.

There actually have been experiments in the detection of gas leaks using PSO . They combined PSO with Fuzzy Logic Control. The addition of FLC allowed the robots to move around obstacles. In this experiment they only tested the robots on a two dimensional plane, but it did have some promising results. If no model was used, it took an average of 1069.8 iterations for the robots to find the gas leak. If PSO was used in combination with FLC, it took only an average of 223.4 iterations.

Logbook

Week 1 and 2

Name	Student ID	Time spent	Tasks
Jasmijn de Joode	1358073	4.5h	Write deliverables (0.5h), Do research (4h)
Robin Foppen	1394746	4.5h	Do research (4h), Write deliverables (0.5h)
Mirre Bosma	1266489	4h	Write problem statement (1.5h), Do research (2.5h), Write wiki page (0.5h)
Dirk de Leeuw	1358081	4.5h	Problem statement (2h) Research (2.5h)
Job van Heumen	1380036	5h	Do research and write state of the art (4.5h), write wiki page (0.5h)

Week 3

Name	Student ID	Time spent	Tasks
Jasmijn de Joode	1358073	3.5h	Research legged robots (3h), edit wikipage (0.5h)
Robin Foppen	1394746	4h	Drone research and writing (2.5h), update wiki (0.5h), step 2 research (1h)
Mirre Bosma	1266489	7h	Research what needs to be done in case of collapse (4.5h) Order wiki page, add short summary begin sections and reference correctly (1h) Do research to what is needed to screen a building and come up with ideas for robots (1.5h)
Dirk de Leeuw	1358081	3h	Research Wheeled and tracked robots(3h)
Job van Heumen	1380036	5h	Research about the inspection of damaged buildings (5h)

Week 4

Name	Student ID	Time spent	Tasks
Jasmijn de Joode	1358073	6.5h	Meeting about requirements (1h), Research on robot swarms/bees (1.5h), editing wiki (legged robots) (1h), write problem statement and deliverables (3h)
Robin Foppen	1394746	5.5h	Meeting about requirements (1h), Research on robot bees (1.5h), editing wiki (1h), writing USE section (2h)
Mirre Bosma	1266489	5.5h	Research to robot swarms (1.5h) Work on wiki(2h) Meeting about requirements (1h) Research and write PSO (1h)
Dirk de Leeuw	1358081	h
Job van Heumen	1380036	5h	Meeting about requirements (1h), writing and editing wiki (robo bees) (1.5h), research robot swarms (2.5h)

Week 5

Name	Student ID	Time spent	Tasks
Jasmijn de Joode	1358073	h
Robin Foppen	1394746	h
Mirre Bosma	1266489	h
Dirk de Leeuw	1358081	h
Job van Heumen	1380036	h