Kostas Alexis's Posts (12)

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DARPA Subterranean Challenge - Team CERBERUS

Dear community,


We would like to inform you about our participation in the DARPA Subterranean Challenge as Team CERBERUS (University of Nevada, Reno, ETH Zurich, Sierra Nevada Corporation, University of California, Berkeley, Flyability). 

Please find out more for us through by watching our concept video:

And by vising our website: https://www.subt-cerberus.org/

We look forward to the novel research of this Challenge! 


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This is to share results on radiation source localization in GPS-denied environments using autonomous aerial robots that estimate the nuclear (Cs-137 in the experiments) source location and intensity, while simultaneously planning for informative measurements. Smart selection of measurement points is critical as the robot has to dwell for sufficient time to allow the Poisson statistics to derive a confident measurement. The robot is equipped with CsI(Tl) scintillator with silicon photomultiplier and miniaturized electronics for counting and spectroscopy. The first video is explenatory of our approach while the following is taking place in a more realistic environment: 

Additional details:

* Autopilot: PX4

* Position Controller: Linear Model Predictive Control running on an INTEL NUC (ROS)

* Localization: Visual-Inertial 

* Path Planning: Explicit function to optimize for distribution of measurements

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Dear community members,

During this ICRA we presented our work on "Uncertainty-aware Receding Horizon Exploration and Mapping using Aerial Robots".

This work is now accompanied with an open sourced ROS toolbox available at: https://github.com/unr-arl/rhem_planner 

These videos present the planner in operation:


In case you find it interesting, we would be happy to support you in order to fully integrate it in your research.



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Robotized Radiation Mapping

Dear community members,

This is very preliminary work on aerial robotic radiation detection in real-time and in a GPS-denied manner. The robot localizes based on visual-inertial data and integrates a deferentially installed 2-radiation detectors solution to exploit their polarity characteristics. Most of the research is ahead but we feel the topic is exciting and would like to communicate it to all of you. In this link you can get updates of our relevant work: http://www.autonomousrobotslab.com/robotics-for-nuclear-sites.html ;

As shown, it is not only referring to the radiation detection itself but also to the relevant challenges involved such as the autonomous navigation in visually-degraded environments:



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We would like to share two of our recent and ongoing results related to autonomous exploration and mapping in darkness. As opposed to approaches that rely on localization based on LiDAR systems, the videos below rely on visual-inertial localization with LEDs illuminating the scene appropriately. For the first case, visible-spectrum cameras are used, while for the second near-infrared cameras are employed. We believe that operation in darkness is an important feature for aerial robotics and we would like to see more in that direction. 

For more please visit: http://www.autonomousrobotslab.com/ 

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Hi all, 

We recently released this video on autonomous exploration and inspection. Have a look!


The robot employs its visual-inertial navigation system in order to localize itself in the environment and simultaneously map it and 3D reconstruct it. Based on the newly proposed "Receding Horizon Next-Best-View Planner" the robot computes the next best step for efficient volumetric-exploration of unknown spaces. This is achieved by predicting a sequence of next-best-views via sampling-based methods and information gain approaches, executing only the first step and then repeating the whole process in a receding horizon fashion. Once full volumetric-exploration has been achieved, the robot starts focusing on the surface reconstruction of objects of interest in the environment.


A. Bircher, M. Kamel, K. Alexis, H. Oleynikova, R. Siegwart, "Receding Horizon "Next-Best-View" Planner for 3D Exploration", IEEE International Conference on Robotics and Automation 2016 (ICRA 2016), Stockholm, Sweden 

The paper is accepted and will be presented at ICRA this year. 


The code is to be open sourced and will be available once the paper is presented but also before. Send us an e-mail if you have interest already and we will update you once it is out. 

Previous relevant work (but at the problem of optimized inspection while known a geometrical model of the structure):

A. Bircher, K. Alexis, M. Burri, P. Oettershagen, S. Omari, T. Mantel, R. Siegwart, "Structural Inspection Path Planning via Iterative Viewpoint Resampling with Application to Aerial Robotics", IEEE International Conference on Robotics & Automation, May 26-30, 2015 (ICRA 2015), Seattle, Washington, USA .



Hope you like it!

Kostas Alexis


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Wireless sensor network control Drones?

Hello to community!

It is a great fact that UAVs tend to miniaturization. Despite the high technology advances on microprocessors and embedded systems it is clear that only simple control laws can be implemented into Miniature Autonomous Vehicles. Note that i am not talking for rf manned control but for fully autonomous solutions. So what about Wireless Sensor Network control for Drones? It is an idea implemented widely in ground robots. The main approach is to implement on-board only the main control functions (for example stabilization with simple PID loops for safety mainly when the wirelless network is not availible for some reasons) and let advanced control laws send commands from the ground station. Obvioysly the drone will also send its state vector through the network. What's your opinion?

| Ground Station | <---- WSN ----> | DRONE |
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New Advanced Servo Controller

Hello to all community members.

I have just received to my e-mail this new and very improved servo controller:


You can find product details at: http://www.01mech.com/supermodified

I copy the following from the site:

PID Speed / Position controlAccurately adjust your servo’s rotation speed according to your project’s needs
Profiled position/speed controlNo more jerky motions on your robots, only smooth transitions from one setpoint to thenext
Velocity feedbackFeedback on the exact speed of your motor – produce more efficient algorithms and better overall robotbehaviour
Incremental position feedbackFeedback based on a 0.08° increments! Store your position in EPROM and recover it afterRESET
Absolute position feedbackKnow your robot’s joint positions straight after controller initialisation. Store your position in EPROMand recover it after RESET
Additional I/OsUse your Supermodified to also control other devices with 4 available GPIOs onthe Supermodified™ MCU board
Additional analog inputsGet feedback from analog sensors with 4 analog inputs on the Supermodified™ MCU board
Ambient temperature measurementAvoid overheating the ‘guts’ of the servo by knowing ambient air temperature
Current feedbackAvoid excessive stresses and easily calculate torque-demand on your servomotor during operation by knowingthe motor’s current consumption
Bus interfaces (I2C, RS485)Everything is on the comms bus! Up to 127 (wt. I2C, TWI interface), 248 (wt. RS485interface) Supermodified™ nodes can be controlled by a single host
Form FactorControl electronics, absolute feedback element, motor drive electronics, motor and gearbox now fitinside a servo. No more messy boards and wires
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Interfacing MATLAB and Arduino

Hi friends!I have just found and tested a Blockset that interfaces MATLAB/SIMULINK and Arduino. You may find this at:http://www.mathworks.com/matlabcentral/fileexchange/24675-arduino-targetI highly suggest this program since it offers rapid prototyping capabilities to the famous and cheap arduino. The guys have build a block that interfaces with the Real Time Workshop of MATLAB and have also implemented C functions for all arduino operations (analog in, out, serial read/write etc.). Despite the fact that the code is obviously bigger one can gain advantage from the quick and abstract way of programming that simulink offers. It is a good work!Happy coding!
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