Catapult

Description：

A catapult is a ballistic device used to launch a projectile a great distance without the aid of gunpowder or other propellants – particularly various types of ancient and medieval siege engines. … We will make a catapult with LEGO building blocks. Equipped with servos and gears, the car has LEGO tower used to carry projectiles.

As the servo rotates to a proper angle then push the long arm backward a projectile will be launched.

How to build up a catapult

Step 1 Required components

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Step 2 Required components

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Step 3 Required components

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Step 4 Required components

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Step 5 Required components

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Step 6 Required components

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Step 7 Required components

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Step 8 Required components

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Step 9 Required components

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Step 10 Required components

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Step 11 Required components

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Step 12 Required components

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Step 13 Required components

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Step 14 Required components

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Step 15 Required components

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Step 16 Required components

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Step 17 Required components

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Set the angle of the servo to 180 degree

Wire servo up Servo	PCB Board
Brown	G
Red	5V
Orange	S2（GPIO23）

Upload the code of the servo to the main board of the Beetlebot car, as shown below

#include <Servo.h>
Servo lgservo;  // create servo object to control a servo

void setup() {
lgservo.attach(3);  // attaches the servo on pin 3 to the servo object
}

void loop() {
lgservo.write(0); // tell servo to go to position
}

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Step 18

Required components

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Wire up

Interface the servo

Test Code：

#include <Servo.h>
Servo lgservo;
#define ML 15
#define ML_PWM 17
#define MR 14
#define MR_PWM 16
#define servo2 3

char val;
char wifiData;
boolean servo_flag = 1;

void setup() {
Serial1.begin(9600);
pinMode(ML, OUTPUT);
pinMode(ML_PWM, OUTPUT);
pinMode(MR, OUTPUT);
pinMode(MR_PWM, OUTPUT);

lgservo.attach(3);
lgservo.write(0);
}

void loop() {
if(Serial1.available() > 0)
{
    val = Serial1.read();
    Serial.print(val);
}
switch(val)
{
    case 'F': car_forward(); break;
    case 'B': car_back(); break;
    case 'L': car_left(); break;
    case 'R': car_right(); break;
    case 'S': car_stop(); break;
    case 'p': lgservo.write(85);servo_flag = 1; break;
    case 'x': servo_down(); break;
}
}

void servo_down()
{
while( servo_flag == 1)
{
    for(int i=55; i>0; i--)
    {
    lgservo.write(i);
    delay(2);
    }
    servo_flag = 0;
}

}


void car_forward()
{
digitalWrite(ML,LOW);
analogWrite(ML_PWM,255);
digitalWrite(MR,LOW);
analogWrite(MR_PWM,255);
}

void car_back()
{
digitalWrite(ML,HIGH);
analogWrite(ML_PWM,0);
digitalWrite(MR,HIGH);
analogWrite(MR_PWM,0);
}

void car_left()
{
digitalWrite(ML,HIGH);
analogWrite(ML_PWM,150);
digitalWrite(MR,LOW);
analogWrite(MR_PWM,105);
}

void car_right()
{
digitalWrite(ML,LOW);
analogWrite(ML_PWM,105);
digitalWrite(MR,HIGH);
analogWrite(MR_PWM,150);
}

void car_stop()
{
digitalWrite(ML,LOW);
analogWrite(ML_PWM,0);
digitalWrite(MR,LOW);
analogWrite(MR_PWM,0);
}

Build up a few target objects with building blocks(object A, B, C, D, E) and keep them in a certain distance away the catapult and connect Wifi.

Click to make the car to face the object A, hold down the button to drive the catapult to launch a building block.

Then release the button to make the long arm return to the original state. Next, let’s check if the object A is hit by the launched block

You can repeat above steps to hit the object B, C and D