Research on Programming and Electronics for Aalto Explorer (Part 2)

This article continues the series of research on Programming and Electronics for AE: Sensors

3. SENSORS

A few important requirements for an efficient ROV system are:

1. Every controllable device on the ROV needs to have its own processing unit and interface.
2. It should be possible to address and control each of the devices separately on the network by the master user at the control station.
3. All the devices on the network should be isolated to maximize system reliability, to provide power isolation and to easily upgrade.

Following is the complete system-block diagram:

The above diagram was modified for the first stage as follows:

Ultrasonic sensors

Ultrasonic sensors, as the name suggests, measure the distance by using ultrasonic waves, also known as acoustic waves, of frequencies above human auditory range. The sensor head emits a high-frequency sound pulse and receives it back on hitting the target. The distance to the target is calculated by measuring the difference in time between the emission and the reception according to the following formula:

Distance D = 1/2 × T × S

Where, T is the time between the emission and the reception, S is the sonic speed. The value is multiplied by 1/2 because T is the time for to-and-fro distance.

The received pulse is evaluated for different sensing purposes:

1. 1. 1. 1. Time of flight (for sensing distance)
         2. Doppler shift (for sensing velocity)
         3. Amplitude attenuation (for sensing the distance, the directionality, or the attenuation coefficient)  

In time-of-flight-based sensing, a pulse is emitted, and the sensor waits for it to return. This limits the speed with which successive measurements are made.

However, in Doppler and attenuation-based sensing, a constant wave of ultrasound may be emitted, and the received wave’s frequency or attenuation is continuously analyzed. This speeds up the measurements effectively, increasing the sensitivity of the sensor.

Navigation unit

A precise navigation system is another crucial part of the ROV. The navigation system may be composed of a variety of sensors that provide information regarding the ROV’s position and movement. The data from all the sensors is calculated to obtain an optimal estimate of the vehicle’s position. We plan to use a navigation unit that consists of a compass, a gyro and depth sensors.

Motion control

Since it will be with a track, we will use the differential velocities approaches with Arduino interface through PWM.

Possible ways of implementing PID:

The self-tuning algorithm will take inputs from the navigation unit and the sonar. Together with the aid of the PID controller, it will assist in obtaining a trajectory that is the closest to the desired trajectory.

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The details on communication and power management will be updated in the next articles. Don’t forget to sign up to our newsletters or join our pioneer group for further updates!