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  • Red Herring

    Red Herring from the frontThe design of Red Herring began after the SAUC-E ’09 competition following the problems that were experienced with Blackghost. Over the previous couple of years, with Blackghost and Big Bertha, the team had experienced a number of problems with reliability which limited the amount of software testing and development that could be done. This had left the software development far behind where it needed to be to achieve the goals of reaching the Arctic. To solve this problem Red Herring was designed and built as a much larger and simpler vehicle than Blackghost to provide a more reliable software development platform.

    The main goals of the vehicle were to be a simple and reliable vehicle that could be easily used to test and develop software and new mechanical or electrical parts. This didn’t produce a hull that was suited to the long term goals but it provided a reliable test platform which aided in component development so future vehicles could be designed with more success.

     

    Red Herring was built throughout the 2008/09 academic year and was entered into the SAUC-E 2010 competition. Despite the simplifications over previous vehicles, it still took the entire years to build and didn’t leave much testing time before the competition. However, by the end of the year, Red Herring was working reliably and successfully completed longer in water testing runs than any previous vehicle.

     

    Following the competition a number of minor hardware improvements were identified and implemented over the period up until Christmas 2010. At that point hardware efforts shifted to the design of a new vehicle, freeing Red Herring for software development and testing. The value of this extra testing time was proved at the SAUC-E 2011 competition where for the first time we were able to demonstrate Red Herring's ability to perform more complex tasks.

     

    Hardware

    Red Herring in the ballasting tank at SAUC-E 2010Red Herring has a very modular and flexible mechanical design. The main structure is provided by a frame which is constructed from 25mm square aluminium t-slot sections. The aluminium t-slot has a cross-section which allows nuts to be slotted into it so the whole frame can be bolted together and any extra components can be easily attached to it. This means it is very easy to change the configuration of the parts and to attach new parts for testing.

     

    There are two waterproof enclosures to house the electronics. The main enclosure, which houses most of the electronics, is made from an aluminium tube which is 20cm in diameter and 70cm long. It has endplates at either end which seal with a double o-ring bore seal to provide a simple and reliable waterproof seal. The second waterproof housing is for the cameras and is made of from a transparent Perspex tube with one end permanently sealed and the other sealed using another double o-ring bore seal.

     

    The vehicle manoeuvres using five commercial Seabotix BTD150 thrusters. These are arranged in the same configuration as on previous vehicles with two vertical thrusters to control depth; two horizontal thrusters to control yaw and enable strafing and a rear thrusters to drive the AUV forwards.

     

    Inside the hull the computing power has been increased over pervious vehicles with an ASUS AT3N7A-I motherboard. That has a 1.6GHz Dual-core Intel® Atom™ processor 330 and a NVIDIA® ION™ graphics card to provide the power required to perform the visual processing. The AUVs power is provided by four 4.5Ah 19.5V lithium iron phosphate batteries, with a custom battery module that monitors the cells and enables in hull charging.

     

    Red Herring is also equipped with a suite of sensors to aid navigation and sense its surrounds. Navigation is assisted by an Xsens MTi and pressure sensors. The Xsens MTi measures lateral and rotational accelerations and orientation using accelerometers, gyros and a magnetic compass. The pressure sensors measure the water pressure so the depth of the vehicle can be calculated. In addition, Red Herring uses two cameras, a sector scanning sonar and three hydrophones to build a representation of the environment around it. This allows it to perform a number of different tasks and mission.

    Software

    The software for Red Herring was built on the software from Blackghost with an extra year of development to improve and extend it. The design is based around a distributed, modular system, where each module runs as a separate process independently of the others. The modules communicate with each other using a custom message protocol, where messages are sent using SPREAD, an inter-process communications toolkit.

     

    The bulk of the software is written in C++, with other languages used where appropriate.  For the 2010 SAUC-E competiotion we used ‘Missions’, which describe the AUV’s behaviour in a given session in the water, written in Python and a GUI for ROV operations, testing and initialisation is written in Java and Qt. For the 2011 competition we formalised these 'Missions' into a more complete AI, using environmental conditions to decide what behaviour to use. In addition the GUI was converted to C++ to reduce the burden on cross-language support.

    Aside from these modules, we also had:

    • Control – controlling the motors, reading inertial and pressure sensor data, and maintaining position, heading and speed using control loops
    • Image Processing – Reading images from the web-cameras, processing the images with object detection, and outputting object data.
    • Sonar – Communicating with the sonar on a low-level serial connection, interpreting the results and sending them to the image processing.

    For more information about the technical aspects of Red Herring you can read our journal from the SAUC-E 2010, which is available here.

    Specification

    Hull: The main hull is a 70cm long, 20cm diameter aluminium tube mounted within an aluminium frame which is 1.8m long and 30cm square in cross section.

     

    Camera Housing: In addition to the main waterproof hull, the AUV has a second waterproof camera enclosure at the front of the vehicle which contains a forward and a downward looking camera


    Propulsion: Propulsion is provided by 5 Seabotix BTD150 thrusters. They are arranged with a pair of vertical thrusters, one at the front and one at the rear, to control depth; a pair of horizontal thrusters, one at the front and one at the rear, to control turning and strafing and a forward pointing thrusters at the rear.

     

    Computer: The AUV uses an ASUS AT3N7A-I motherboard which has a 1.6GHz Dual-core Intel® Atom™ processor 330 and a NVIDIA® ION™ graphics card in a mini-ITX form factor (17.1cm by 17.1m).

     

    Power: The AUV is powered by four 4.5Ah 19.5v LiFePO4 packs, with a battery system that supports full cell monitoring and in hull charging.

     

    Cameras: Two Logitech Quickcam Pro 4000 web cameras are used (one looking forwards and one looking down) to find objects near the vehicle.

     

    Sonar: A Tritech SeaSprite Sonar is used to provide an acoustic picture of the area around the vehicle.

     

    Navigation Sensors: The vehicle is equipped with an Xsens MTi is used to provide orientation and acceleration data to aid navigation and two pressure sensors to provide depth information.

     

    Hydrophones: Three H2B hydrophones from Aquarian Audio Products enable the vehicle to detect acoustic pingers and their direction relative to the vehicle.