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12. Mechanical Design, Machine Design

Mitq

The idea of the Solar tracker was given by our Fab Academy instructor at Fab Lab Dilijan, Onik Babajanyan. Since Armenia is a sunny country, we liked his suggestion. If we obtain an efficient solar tracker, we will be able to get maximum energy from the sun throughout the year. We started studying the existing types of solar trackers, which were numerous, but we were not able to obtain accurate information about all of them; however, we obtained information about 5 types, which are currently relevant worldwide. These are: 1.Single Axis Solar Tracker 2.Dual Axis Solar Tracker 3.LDR Based Solar Tracker 4.GPS Based Solar Tracker 5.Hybrid Solar Tracker

  • Single Axis Solar Trackerը It is a system that moves along one axis, which moves in one direction—east and west. Its advantages include a simple structure and fewer motors. To learn more, follow the link.

  • Dual Axis Solar Tracker It is a two-axis system that moves left-right and up-down. Its advantages are the highest efficiency and the ability to obtain more energy. Its disadvantage is a more complex mechanism than Single Axis.

  • LDR Based Solar trackerիLDR photoresistors are used in its construction; it determines the direction of the sun based on light intensity. It is simple, cheaper, and suitable for an educational project.
  • GPS Based Solar Tracker GPS is used; it calculates the time and location data, and determines the position of the sun based on the location. It is very accurate and does not depend on light sensors, but it is more complex from a programming perspective.
  • Hybrid Solar Tracker It combines several methods; it is the smartest option and has the highest accuracy, as it uses GPS and LDR sensors, a dual-axis system, and calculations based on various algorithms. However, it is the most complex in its structure.

Based on our research, it became clear that the best option for us is the LDR Based Solar Tracker with a dual-axis system.

Component study

### Photocell (photoresistor).

Since one of the main components of the LDR (Light Dependent Resistor) type is the photoresistor (LDR, Light Dependent Resistor).](https://3drob.ru/stati/pro_arduino/radiokomponenty_1/fotorezistor_datchik_osveshyonnosti) It is a passive electronic component whose resistance changes depending on light. When the light increases, the resistance decreases; when it gets darker, the resistance increases. And learn how to correctly place it on the PCB board and what calculations need to be taken into account.

For the board, I needed 4 passive sensors, as well as 4 pieces of 10 kΩ resistors based on that.

And since my PCB model had specific requirements that the components had to be placed at equal distances from each other, the photoresistors had to be separated by the partition walls of my 3D model. Taking that into account, I modified it in this way, and during further work the effectiveness of the modification will be visible.

Testing Mator

And also we needed motors to provide vertical and horizontal rotation. Two types of servo motors were considered by us. - Servo drive CORONA CS-939MG (2.5 kg/cm, 0.14 sec/60°, 12.5 g) - HobbyKing™ HK15138 Standard Analog Servo( 4.3kg / 0.17sec / 38g)

And since our microcontroller was Arduino Uno, and we needed the current of the two motors not to exceed 500 milliamps, we stopped at that point.Servo drive CORONA CS-939MG (2.5 kg/cm, 0.14 sec/60°, 12.5 g)

They helped us.Arduino Docsfrom the code posted on the official website

#include <Servo.h>

Servo myservo;  // create servo object to control a servo
// twelve servo objects can be created on most boards

int pos = 0;    // variable to store the servo position

void setup() {
  myservo.attach(9);  // attaches the servo on pin 9 to the servo object
}

void loop() {
  for (pos = 0; pos <= 180; pos += 1) { // goes from 0 degrees to 180 degrees
    // in steps of 1 degree
    myservo.write(pos);              // tell servo to go to position in variable 'pos'
    delay(15);                       // waits 15ms for the servo to reach the position
  }
  for (pos = 180; pos >= 0; pos -= 1) { // goes from 180 degrees to 0 degrees
    myservo.write(pos);              // tell servo to go to position in variable 'pos'
    delay(15);                       // waits 15ms for the servo to reach the position
  }
}

which would rotate 180° and return to its initial position, and we started applying different load resistances to the servo motor in order to understand whether it would be sufficient to implement our project.

  • We tested the motor in a horizontal position by gradually increasing the load.
  • And in the vertical direction, we hung the load from a piece of plywood attached to the motor.

And the servo motor we selected was sufficient to properly ensure the movement of our project, meaning that with two motors of the same type, the Arduino Uno will be able to supply power to them. Now we have a ready working PCB with 4 passive sensors, and servo motors that have passed different testing stages. These two data are enough to start my favorite part — sketching, because for me it is easier to begin 3D modeling after drawing a hand sketch.

Group Assignment — 3D modeling

Սկբնական էսքիզ

After discussing the initial sketch, and taking into account the requirements set before us, the model had to be designed accordingly

  • as lightweight and compact as possible

-The wires and mechanisms had to operate inside it without any obstruction.

  • And we had to design it in such a way that the wires would not be visible.

We discussed all of that and came to the conclusion that we needed a single sketch in which all the listed requirements would be taken into account

Final sketch

And based on this sketch, we started our 3D modeling phase and divided the work into two parts. Ani will model the section where the Arduino Uno and the horizontally operating motor will be placed, while I will design the part that will be mounted on the motor shaft, through which the wires will pass and reach the vertical motor. On that motor, a vertical arm will be attached, through which the wires will pass and reach our PCB board, which in turn will be fixed at the upper part of the arm, where the partition section for our 4 sensors will be located.

- I already had the 3D model of my PCB from KiCad

- And I also downloaded the3D model of the servo motor from the internet, and these also served as a basis in this modeling stage.

  • The KiCad 3D file served as the basis for starting the 3D modeling. This is a very important part for the accurate and smooth operation of my entire work. I had to not only precisely indicate the locations of the passive sensors, but also the mounting points of the board. At the very top, there had to be a separating wall for those four passive sensors, with a height of 15 mm.

- I should also note that the passive sensors are mounted opposite to the board. The board must be positioned at the bottom of the body so that the passive sensors, passing through the holes, can absorb the sun’s rays. The pins will be located at the bottom, and all connections should be made from there. We also had the challenge of keeping the wires as unobtrusive as possible.

For this reason, a rectangular tube-shaped body was extended from the upper part. Since the lower part could come into contact with other parts of the mechanism, I decided to make it semicircular. The radius of the circle was 13 mm, and at its center I created a double-sided circular отверстие with a radius of 3 mm. This was done so that later the star-shaped mechanism attached to this body could be connected to the servo motor.