University of Cambridge Logo


  • Big Bertha

    Big Bertha ImageBig Bertha was the first vehicle that the team built in the academic 2006-07 and was entered into the 2007 SAUC-E competition. Its construction taught the team many valuable lessons which were built on during the construction of the next vehicle, Blackghost.

     

    The vehicle was designed with the aim of deploying through a bore hole, which motivated the thin cylindrical shape. The hull was made from an acrylic tube and was split into three sections to divde the different components of the vehicle. The front nose cone and rear tail cone were also machined from solid blocks of acrylic to provide a hydrodynamic shape. The vehicle is manoeuvred using two a of thrusters, consisting of a vertical and horizontal thruster, at the front and another at the rear. These allowed the AUV to dive, control its pitch, strafe and turn on the spot enabling a large number of tasks to be performed with maximum simplicity. A main motor and prop at the rear also allowed forward and backward motion.

     

    The AUV was powered by a balloon board, developed by Cambridge Engineering Department. This uses a 520MHz arm processor and is enclosed in a very small form factor which allowed it to be easily mounted in the AUV. It also used a custom build board, which communicated with the balloon board using a serial connection and read in data from the sensors and controlled the motors.

    Technical Specification

    Hull: The main hull was 1.1m long and 90mm in diameter and was made from a perspex tube. It was made in five sections; a front nose cone, a rear tail cone and three central sections to hold the thrusters and main electronics.

     

    Main Propulsion: A Graupner Speed 720 BB Torque motor with a 6 bladed propeller at the rear of the AUV provided the main propulsion. This gave the AUV a forward travelling speed of approximately 2m/s.

     

    Manoeuvring Thrusters: Two pair of horizontal thrusters (one at the bow and one at the stern) gave left/right manoeuvrability, and a pair of vertically mounted thrusters (again bow and stern) gave control of depth and pitch. The thrusters were paddle thrusters which used a rotating paddle to force water one way or the other and were powered by Graupner Speed 400 motors.

     

    Computer: A balloon board, which was a board in development by the Cambridge University Engineering Department. It runs an Intel PAX27xxx processor running at 520MHz which had a camera data interface call quick capture allowing digitised camera pictures to be easily processed. The board also had an FPGA which could be used for digital signal processing operations. The board was small and light, measuring 113 x 56 mm and weighing only 30g.

     

    Power: The AUV was powered by 32 1.3v 2500mAh AA NiMH batteries. They were arranged in two packs with 10 in series to power the computer and electronics and two packs of 6 in series to power the thrusters.

     

    Camera: The AUV had one forward looking camera, which was a Genie GC300H/SH P with a 2.1mm lens. This produced a 1V pp 75C pal output with a 752x582 resolution which was passed into an Analog devices ADV71180 video decoder IC to convert it to a digital signal for the balloon board.

     

    Marker Dropping Module: On of the tasks the AUV had to complete was to drop a marker on a target so it had a marker dropping system. This worked using a strong permanent magnet to hold the marker in place with an electromagnetic coil behind it, which was used to briefly counter the flux from the permanent magnet and release the marker. The electromagnet was only used when releasing the markers so power consumption was minimal