4-Legged Spider Robot With 3D Printed Parts (8 Servo Motors and an ESP32)

4-legged walking robot with 3D printed parts

In this project, I will show you how to make a simple 4-legged walking spider robot using 3D printed parts. The design consists of only five main parts, including the top and bottom plates, arm connectors, legs and servo holders. The 4 legs of the robot consist of four arm parts and four leg parts. A total of eight hobby servo motors are used for the robot movement, four in the arms and four in the legs.

On the circuit side, an ESP32 board was preferred, but the project can be easily controlled with Arduino boards. The Bluetooth feature of the ESP board was preferred for wireless communication and a simple application was created for control. The app allows you to control the robot's movements such as walking, turning and jumping with simple commands.

This project is easy to assemble and use, making it a great choice for students, teachers or anyone interested in robotics. Let's get started!

Placing the Arm Servos on the Base

First of all, before assembling the Servos, the Arm Servos to be placed on the base must be adjusted to the 90 degree starting position. I have shared a basic code for the initial positions. As you can see, I have fixed 3 Servo motors, let's mount the fourth and last Servo motor together.

The holders on the servo base may remain slack according to the type of Servo motor, in this case, you can keep it fixed with the help of some hot glue.

In the project, 8 pieces of SG90 Micro Servo motors (or equivalent in approximate dimensions) were used.

Product: SG90 Servo
Torque: 2.0kg/cm(4.8V), 2.2kg/cm(6V)
Speed: 0.09s/60°(4.8V), 0.08s/60°(6V)
Rotate angle: 180°
Operating voltage: 4.8 ~ 6V
Gear: plastic
Dead band: 7us
Weight: 10.5g
Dimension: 22.8mm × 12.2mm × 28.5mm

Downloads

01-plate.stl

01-srv_holder.stl

Spider_Servo_Initial_Positions.ino

Fixing the Arm and Leg Connectors

In this section, fix the Arm and Leg connectors, which consist of 2 separate parts, together with a bolt and nut. Attach the fixed connector to the base Servo. Then, with the connector at a diagonal angle, place the Servo Horn and fix it to the Servo motor by tightening the screw.

Finally, fix the end of the Servo Horn to the connector using a screw, it is not necessary to do this but fixing it prevents looseness. Now that the arm is complete, let's move on to leg assembly.

Downloads

01-connector.stl

Assembly of the Legs

Before fixing the servo motors to be used in the leg, you need to bring them to a starting angle of 60 degrees. Then place the holder and leg part, fix the leg part to the Servo motor with the appropriate screw.

Insert the leg into the connector and attach the Servo Horn so that the leg is in the right angle position. Then fix the Servo Horn with the screws.

Now prepare the other three legs and complete the assembly. Now that the assembly of the arms and legs is complete, we can move on to the power part of the circuit.

Downloads

01-foot.stl

01-srv_holder.stl

Power of the Circuit

A 7.4 volt battery will be enough for the circuit, the base part was designed for the size of a 3S Li-Po battery, but the battery in my workshop was damaged and I had to use an 11.1 volt battery. If you are going to use a 7.4 volt battery you can skip this part.

I placed the battery under the base and fixed it with a cable tie. Due to the battery change, I included a voltage step-down module in the power circuit. I set the voltage output to 7 volts with the help of the adjustment screw on the module and connected the battery inputs.

After placing the module on the base, let's continue by assembling the upper base where the circuit board will be fixed. All the parts of the robot are assembled, let's move on to the circuit board!

Circuit Board

I designed a circuit board that controls 16 Servo motors and can be attached to an ESP32 board. As always, I chose PCBWay for high-quality circuit board prints. You can visit this link to order PCB, Circuit and Gerber files:

https://www.pcbway.com/project/shareproject/Simple_3D_Spider_Robot_4_Legged_Walking_Design_ESP32_48834275.html

Easy solderable components are preferred, basic soldering knowledge will be enough. Alternatively, you can use PCBWay's assembly service and order a ready soldered circuit. Mount the required components on the PCB and solder them in place with a soldering iron and soldering wire. You can see the location of the components in the uploaded image.

4x 100uf 25V~16V Capacitor for Power
4x 470uf 25V~16V Capacitor for Servo Motor
1x SB560 Diode for Power
1x 7805CV Voltage Regulator for Power
2x 3mm-LED
16x 220-ohm Resistor for Servo Motors
2x 330-ohm Resistor for LEDs
1x 2pin 5mm Screw Terminal for Power input
2.54 Female Headers for ESP32 Board
2.54 Male Header for Servo Motor Connections
Doit ESP32 Devkit V1 development board

Is the use of this breadboard or different projects that have been done necessary? Here are a few project links below:

Connection of Servo Motors

Let's place it on the robot and then make the servo motor connections. Below are the GPIO pins to which servo motors are connected:

// Servo motor pins

int srv_footA = 13; //Leg A GPIO 13

int srv_armA = 12; //Arm A GPIO 12

int srv_footB = 15; //Leg B GPIO 15

int srv_armB = 2; //Arm B GPIO 2

int srv_footC = 26; //Leg C GPIO 26

int srv_armC = 25; //Arm C GPIO 25

int srv_footD = 17; //Leg D GPIO 17

int srv_armD = 5; //Arm D GPIO 5

The robot is almost ready, remove the ESP32 board and connect it to your computer, then open the shared source code. Now it's time to code!

Source Code

Open the code in Arduino IDE

First, you need to open the provided code in Arduino IDE. This will allow us to edit and upload the code to the ESP32 board.

Add the ESP32 board URL in Preferences

Go to File > Preferences and add the ESP32 board manager URL:

https://dl.espressif.com/dl/package_esp32_index.json

This step ensures that we can install the necessary ESP32 tools.

Install the ESP32 board package

Now, go to Tools > Board > Board Manager, search for “ESP32,” and click Install.
This process adds the ESP32 board support to the Arduino IDE.

Include the required libraries

The code includes two libraries:
BluetoothSerial.h is used to handle Bluetooth communication.
ESP32Servo.h is a library specifically designed for controlling Servo motors with ESP32 boards.

1.Commands sent via the mobile app

The application sends designated numbers via Bluetooth to activate generated commands such as up- down-walk and others. These numbers are defined in the app, and the commands are interpreted in the code to trigger different robot movements.

// Commands sent via the mobile app through Bluetooth

//UP = 50

//DOWN = 51

//WALK = 52

//ROUND = 53

//BLINK = 54

//STALL = 55

2.Define GPIO pins for Servo motors

In this section we specify the GPIO pins to which the Servo motors are connected. Each arm and leg of the robot is controlled by separate Servo motors.

Servo servo_footA;

Servo servo_armA;

Servo servo_footB;

Servo servo_armB;

Servo servo_footC;

Servo servo_armC;

Servo servo_footD;

Servo servo_armD;

// Servo motor pins

int srv_footA = 13;

int srv_armA = 12;

int srv_footB = 15;

int srv_armB = 2;

int srv_footC = 26;

int srv_armC = 25;

int srv_footD = 17;

int srv_armD = 5;

3.Set movement limits and speed

The robot's movements are defined with specific limits for the arms and legs. The speed of these movements is controlled by the Speed variable.

// Movement limits and speed settings

int Fdw = 60; // Foot down limit

int Fup = 80; // Foot up limit

int Abw = 70; // Arm backward limit

int Afw = 110; // Arm forward limit

int spd = 3; // Movement speed (~2-5)

4. Bluetooth connection and data handling

In the loop section, the code checks if any data is received from the Bluetooth app. If data is available, it is read and stored in the Data variable. Based on this data, specific robot functions are triggered.

void loop() {

if(SerialBT.available()){

BTData = SerialBT.read(); // Read data from the Bluetooth app

}

5.Trigger robot actions based on commands

When a command is received, the robot performs actions like walk-rotate or reset to a stable position. That's the working principle and requirements of the code, now upload the code to the board and then let's move to the application side.

// Execute commands based on received data

if (BTData == 53) {

digitalWrite(p13, HIGH);

ROUND();

digitalWrite(p13, LOW);

} else if (BTData == 52) {

digitalWrite(p13, HIGH);

WALK();

digitalWrite(p13, LOW);

} else if (BTData == 54) {

BLINK();

for (int i = 0; i < 7; i++) { WALK(); }

stall();

flat_up();

delay(1000);

flat_dw();

delay(1000);

for (int i = 0; i < 7; i++) { ROUND(); }

delay(500);

stall();

} else if (BTData == 50) {

flat_up();

} else if (BTData == 51) {

flat_dw();

flat_up();

} else if (BTData == 55) {

stall();

digitalWrite(p13, LOW);

}

Downloads

Spider_ESP32_BLE_Code.ino

Bluetooth Control Application

We will be using MIT App Inventor, a free and drag-and-drop tool for developing Android apps. After logging into App Inventor by email, upload the shared AIA file of the app I created. (The AIA extension file is not supported here for attachment, so I had to upload the file to the PCB page) This way you can examine the blocks and build your own Android installation file without any trust issues. Then all you need to do is install the app on your phone or tablet!

Now let's talk a little bit about the interface of the app, there is a button to list Bluetooth devices, just below it I added a Text Label showing the connection status. Finally, I added 6 buttons to trigger the robot's motion functions. In the block section, there are a few conditions that initiate Bluetooth communication at the very beginning. Then the data type and data functions to be sent for each movement button were created. It's that simple, now we have an application! Now it's time to control the robot!

Thanks for reading, I hope it has been a helpful resource for your projects. Have a great making!