Robotic Fish

This project can be made for entertaining purpose as well as other productive functions like detecting breakage or leakage in pipes or the water storage wells, like pools. This can be done by interfacing a camera in the front, with the help the live feed which will process the data thereafter will be sent to the user via a transmitter and receiver at both ends. But this project is a prototype, where the model swims in water with the help of the motion of it's tail.

There were many challenges faced during this project, since, the body has to be submerged in water it requires insulation as there is internal embedded system and the electrical components facilitating the forward motion of the fish.

Embedded System:

The platform (controller) where the rotation of the motor has to be controlled precisely by a specific angle along with that it has no other component to control other than the motor, that is why Arduino Uno has been used, as less number of digital pins are required for connections. Also, it reduces the overall cost of the project. 

Servo Motor:

Servomechanism is basically a closed-loop system, consisting of a controlled device, controller, output sensor and feedback system. The term servomechanism applies to the systems where position and speed is to be controlled, thus requiring a feedback.

The internal block diagram of servo is as follows:

Figure 1.1: The internal block diagram of servo motor.

Here, the electrical energy is converted to mechanical energy, by looking at the diagram it can be seen that this is a closed loop feedback system. There is an internal DC Motor which is connected to a gear pair having low speed reduction ratio. This gear pair is further connected to another gear pair having the same number of teeth, which is then connected to the Potentiometer through a shaft, hence, the value of resistance changes. The output terminal of potentiometer is connected to the Non-inverting end of the Operational Amplifier (here, it is a comparator), and the Inverting end is given a Vref  voltage signal. Initially, when the DC motor is rotating the POT via the gears, the resistance or we can say the voltage changes which is being fed continuously to the comparator. The moment inverting and non inverting voltage of the Operational amplifier becomes equal, the output of comparator is 0 Volts, the DC motor stops and hence, the motor holds it's position the moment  V(+)=V(-).

The reference signal provided is nothing but the PWM signal which can be changed by adjusting the Turn ON and turn OFF time hence, the angle of servo motor can be controlled accordingly.

The resolution of the servo motor describes the accuracy of the angle, and hence it holds that position until the Vref is unchanged. The servo motor here changes it's position from 0 to 180 degrees in steps of 1 degree. hence, by changing the PWM duty cycle, the angle of rotation can be controlled.

Figure 1.2: The PWM Duty cycle given at Vref to get the accurate angle.

In this project, the servo is connected to the thermocol. And the specifications of the servo motor used is as follows: Provides 1.8kg/cm at 4.8V and 2.2kg/cm at 6V.

Body:

The body had to cut through the water, so we used the streamlined nature of the fishes.The streamlined body, helps in cutting through water and to facilitate a forward motion.Since we required the shape of a fish, we chose thermocol as the body material of the fish and also helped in cost reduction.

Hence, to cause the forward motion of the fish, the body was divided into 3 parts, 1 which held the Arduino Uno board, 11.1 Volts Li-Po battery and the connecting wires. And the other 2 parts had the individual servo motors attached.

Figure 1.3: The thermocol fish body, without insulation, having the respective placement of the servo motors and Arduino Uno.

Insulation:

The most challenging part of this project was to insulate the fish from water, else the components and the body would get damage by the water entering inside the electrical portion. To avoid the contact of water with the fish, the insulation here was done with the help of plastic which prevented penetration of water inside and also didn't hamper the movement of the tail.

Figure 1.4: The body of the fish after insulating it with plastic and proper placement of the Battery, Servo motors and Arduino Uno.

Weight:

It was difficult to balance the fish inside water as it would incline in either directions due to unbalanced centre of gravity, so the temporary weights were suspended along with it to make it balanced and also to immerse in water partially but not sink in water, so it was done with the concept of Centre of Gravity and Centre of Mass. 
Thermocol is lighter than water, it was required to be weighed down using weights or else the fish would be floating at the water surface.

Figure 1.5: The complete body of the fish before immersing it in water and the weights have being suspended.

The final demonstration:

Figure 1.6: Fish inside tub

To see the video demostration of this respective project, go to the following link: https://www.youtube.com/watch?v=TycD3QYpdko

The code will be available to blog followers upon request. :)