1 Lab+Hwk 2 - (DISAL) at EPFL
Contents
1. I How robust is your new controller when the first robot tries to avoid a wall How constant 3 k x x Supervisor is useful agent in Webots See the User Manual for more information on supervisors NC JP CC SC741 Lab Hwk 2 Coordinated and collective movements in Webots Swarm Intelligent Systems Research Group EPFL is the distance between both robots What happens to the effective forward speed of the first robot when the follower is introduced Qs 5 Recall the performance of your flocking controller in Iz What did you observe How does avoiding obstacles affect the performance of the controller Qs 5 What happened when you increased the speed of the leader in S4 Why did this occur Does this reflect what would occur on real robots or is it just an aspect of the simulation environment Qio 5 How does the flocking capabilities of robots that can track the leader with the same bias speeds compare to the previous flocking strategy What about with different bias speeds What does this tell you about the importance of Reynold s different rules Q 5 What would happen if we maintained the same type of system with a designated leader robot and increased the number of followers Recall that the communication abilities will only work for a finite range Can you think of a way which the system could be changed to work better in this situation Q12 5 In this program although they are given the information we do2. following formulas R R amp axle_length le Vri R Ry rl with R and R being the radius of the left and right wheel of robot n respectively and axle_length being the distance between the wheels of a single robot With these formulas you can calculate R R and some term which is constant for any velocity radius pair This allows you to calculate the wheel speeds of the follower robot as a function of their radius with v aR Implement formation flocking behavior using flocking2 wbt leader cc and follower2 cc and save it as follower2 cc In this situation robot 2 can observe the wheel speeds of robot 1 and robot 3 can observe the wheel speeds of robot 2 robot 3 should use the same equations as robot 2 by symmetry You should initially just have the leader travel in a circle with no obstacles but may try more complicated formations if you wish Take note of how the system performs Try changing the leader speed to different values Note what happens when turning if you set the leader speed to a very high value Points for this problem will be assigned based on the answer to the corresponding question in the homework NC JP CC SC741 Lab Hwk 2 Coordinated and collective movements in Webots EPFL Swarm Intelligent Systems Research Group EPFL j doe Figure 1 The robot formation first translates a length T and than rotates along a circle of radius R d represents the inter robot separatio
3. 0 2 First Part Simple Collective Motion In the first lab you programmed an obstacle avoidance behavior using the distance sensors of the Khepera In correll webots you find the worlds flockingl wbt flocking2 wbt and flocking3 wbt and controllers leader leader3 followerl follower2 follower3 and flock_super In all these worlds there will be both leader and follower robots Leader robots are red in color while followers are green Copy all worlds and the controllers into your webots directory The controller Jeader cc enables you to control a robot using the arrow keys on your keyboard The goal of the first part of this exercise is to implement a simple following behavior using the Braitenberg vehicle framework in followerl cc that allows a follower robot to follow a leader robot Remark In order to facilitate the grading of exercise set copy all your controller supervisor and world modules to correll ab02 youruser name webots worlds and correll lab02 yourusername webots controllers NC JP CC SC741 Lab Hwk 2 Coordinated and collective movements in Webots Swarm Intelligent Systems Research Group EPFL only after you finish the exercise World files contain all the information not only for recovering the environment but also the corresponding controllers and supervisor programs make sure that you save them and deliver as part of your solution even if not explicitly mentioned Answer to the theoretical question
4. Swarm Intelligent Systems Research Group EPFL 1 Lab Hwk 2 Coordinated and collective movements in Webots This laboratory requires the following equipment C programming tools gcc make Webots simulation software Webots User Guide Webots Reference Manual The laboratory duration is about 2 hours Homework will be due on the 6 day after your lab session at 5 p m Please copy your solutions plots descriptions doc ps html pdf txt movies and so on into the directory correll lab02 yourusername The directory correll lab02 allows you to write but not to read The corresponding Webots files see section 2 for details should be saved in a sub directory webots Please strictly follow these guidelines to facilitate the grading process and keep in mind that no late solutions will be accepted unless motivated by health reasons doctor certificate required 1 1 Grading In the following text you will find several exercises and questions The notation Ix means that the problem has to be solved by implementing a piece of code and performing a simulation The notation Sx means that the question can be solved using only additional simulation The notation Qx means that the question can be answered theoretically without any simulation Please use this notation in your answer file The number of points for each exercise is given between parenthesis The total sum of the points is for the laboratory and homework part is 10
5. ccomplished using Braitenberg vehicles You will now modify the Braitenberg obstacle avoidance routine to accomplish this behavior I 10 Load flocking 1 wbt The leader robot is controlled by the leader controller to provide manual control Modify the follower controller to obtain a Braitenberg vehicle able to follow the leader robot Save your solution as follower1 cc Hint Have a look at the Braitenberg vehicles that implement light following and avoidance from last exercise what is the difference between them Both range and channel are parameters that can be set in the Scene Tree Window The channel can also be changed dynamically by the robot itself NC JP CC SC741 Lab Hwk 2 Coordinated and collective movements in Webots Swarm Intelligent Systems Research Group 3 Second Part Formation Control For some applications e g lawn mowing vacuum cleaning it might be useful for having your flock maintain a relative formation i e if the robots form a line and the leader turns the line itself turns Figure 1 shows an example of this type of behavior You will now implement relative formation flocking using robot wheel speeds Q2 10 Compute the left and right wheel speeds of robot 2 v12 vr2 as a function of 13 5 S4 robot 1 vu vri shown in Figure 2 1 as they perform a translation of a length T and a rotation in formation of radius R while maintaining the distance d between them Hint use the
6. n t give a physical method by which the follower robots track the relative position of the leader robot What are some ways that this could be accomplished with real robots What might be the pros and cons of these strategies Recall that robots do NOT have access to their global coordinates NC JP CC SC741 Lab Hwk 2 Coordinated and collective movements in Webots
7. n that should be maintained during the movement 4 Third Part Robust Flocking In this part you will attempt to implement flocking using the relative positions of robots Copy the flocking3 wbt world and leader3 follower3 and flock_super controllers to your home directory flock_super is the controller for the world supervisor The robots begin in a diamond formation with the leader at the head The leader will travel a random path around the arena Followers have the leader robot s relative range distance between leader and follower and bearing relative angular offset of the leader s location in radians i e 0 is straight ahead 7 2 is directly right 7 2 is directly left available to them I5 30 Implement a flocking algorithm for the follower robots so that the diamond formation is roughly maintained using the relative leader position and proximity sensors You must still use obstacle avoidance You should use the same forward bias speed for all the follower robots Save your code as follower3 cc S 6 10 Test the robustness of the controller you implemented in question Is with different robot bias forward speeds Randomly assign different bias speeds to each robot within an interval A and quantitatively determine the threshold A where your control schema breaks Higher thresholds will garner more points but will also be more vigorously verified 5 Homework Q 5 Recall the performance of your following controller in
8. s a description of where the files can be found and their names plots movies and so on should be saved instead in the directory correllNab02 ourusername Do not save your controller supervisor and world modules in this directory but use the appropriate subdirectories 2 1 Communication In this lab certain information must be transferred between robots This could be accomplished using wireless radio transmissions or by broadcasting data with infrared Robots that need to communicate have two additional nodes namely an emitter and a receiver node allowing for emitting and receiving data over a fixed range and a dedicated arbitrary channel This will be used to allow robots to track wheel speeds part 3 and relative positions part 4 of other robots 2 2 Flocking Rules In Flocks Herds and Schools A Distributed Behavioral Model in Computer Graphics by Reynolds a successful simulation of flocking is described Reynolds lists several rules which he determines are needed for realistic flocking They are 1 Collision Avoidance avoid collisions with nearby flockmates 2 Velocity Matching attempt to match velocity with nearby flockmates 3 Flock Centering attempt to stay close to nearby flockmates In this lab you will explore the influence and importance of each of these rules 2 3 Implementing a following behavior The most primitive type of flocking is one robot follower following another leader This can be a
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