The aim of this project is to design and construct an underwater, remotely-operated vehicle (ROV), fitted with a 4-axis positioning system, a video transmission system, and a 2-axis (pitch and roll) control system to assist imaging and positional stability.
The project includes the design and development of the PVC frame and water-proof enclosure, design and development of an ARM Cortex-M3 microcontroller-based electronic circuit for the operator interface, and another ARM Cortex-M3 microcontroller-based electronic circuit that controls the seven DC motors fitted with propellers.
A fully operational vehicle has been constructed, though the 2-axis control system and video transmission system remain incomplete.
The electronic design of the top controller centers around a microcontroller (in this case an NXP LPC1768 on an mbed microcontroller development board ) interfaced to: three switches, an LCD screen, two joysticks, and six LED’s
For a system as complex as the top controller, where almost every available I/O pin is being used on the mbed microcontroller, connecting every element simultaneously and then attempting to test and debugging from there, from experience, seemed likely to be inefficient and ineffective.
Instead, an alternative and ultimately successful approach was used, where each element of the top controller was first tested in isolation from the other elements of the system to ensure they performed as required.
The same mbed development system as used in the top controller is once again the central core of the bottom controller system. Three of the six available PWM output channels are used to drive, at variable speed and direction, the H-bridges for the vertical thrusters that require bidirectional control.
A 2-axis accelerometer is used to perform the tilt measurements for the roll and pitch axes used with the self-stabilising control system. If any water is present and causes a bridge across the copper tracks, a positive voltage appears on pin 11 of the mbed. The software is configured to react to this pin going high and transmits a warning signal to the top controller, where an LED is lit, a buzzer sounds and a message appears on the LCD display.
The motors and lights are driven directly off the LIPO’s nominal 11.1 V supply. A 5 V linear voltage regulator, TS7805CZ, is used to reduce the 12 V down to 5V for the mbed. The 3.3 V required by the other logic devices and the RS232 IC is generated by the mbed’s onboard voltage regulator.
The mbed development board includes a USB connection to the development PC. This connection was used, in addition to downloading program code, to give a serial terminal interface direct to the bottom controller for debugging purposes.
To read this external content in full, download the paper from the author archives at mbed.org.