Ultrasonic automatic braking RC car project

Ultrasonic braking is a method of collision avoidance system that can automatically brake the vehicle before an impact. That is whenever any obstruction came in front of the vehicle the system disengages the power transmission to the wheels and activates the braking.

The system works based on the ultrasonic ranging technique which is a non-contact ultrasonic distance measuring method. An ultrasonic braking system consists of an ultrasonic transducer or sensor unit, control unit, and braking mechanism.

The sensor unit consists of a pair of ultrasonic transducers, a transmitter, and a receiver.

The ultrasonic transmitter which is placed in the front of the vehicle will continuously transmit the ultrasonic waves in a fixed range. The transmission transducer generates the ultrasonic waves from a 40khz square wave output generated by the Arduino, which is fed to the transducer after amplification.

An ultrasonic transducer is a component that converts the electrical energy to ultrasonic energy and vice versa; the same transducer can generate and sense the ultrasonic signals.

The ultrasonic receiver which is placed parallel to the transmitter receives the ultrasonic signals that are reflected from the obstacle. Then these reflected waves or signals are fed to the Arduino. The Arduino calculates the distance to the object from the duration of time taken between the transmitted and received waves. Then it checks whether the distance to the object is safe to move forward or the vehicle requires braking. If the distance is less than the safe range then the system will activate the braking.

Refer: » Servo motor interfacing with Arduino

» Arduino Relay module interface

In the here system the Arduino turns the servo motor from an angle of 45 degrees to 0 degrees. And simultaneously it energizes the relay to disconnect the motor supply. The servo arm is mechanically arranged to brake the shaft of the RC car. It is similar to a disc brake arrangement that uses calipers to squeeze the pad against the disc which is attached to the axle. When the obstruction in front of the sensor unit is removed the system returns to the normal state. Then the servo returns back to 45 degrees and the relay to NC (normally closed) position. In the normal state, the vehicle can drive forward without any system interruption.

Without any mechanical arrangements, the braking can be done by electrically also by shorting the motor terminals to brake mode.  For advanced project applications,  a pneumatic braking mechanism also is used.

Ultrasonic braking using HC-SR04 module

The above ultrasonic braking system is used with a pair of transducer modules with amplifier circuits. The system can be built with an HC-Sr04 ultrasonic module which is more feasible and provides better accuracy.

Refer to the above link of the non-contact distance measuring for ultrasonic module interface with arduino.

Code

#include <Servo.h>

Servo servo;

const int  trig = 2, echo = 3 , relay  = 7;
int distance = 20, normalpos = 40 , brakepos = 0;
// Minimum distance for braking 20 centimeters.
void setup()
{
  pinMode(trig, OUTPUT);
  pinMode(echo, INPUT);
  pinMode(relay, OUTPUT);
  servo.attach(9);
}

void loop()
{
  if (radar() < distance) {
    servo.write(brakepos);
    // servo shaft angle for apply brake.
    digitalWrite(relay, HIGH);
    // To disconnect motor supply
  }
  else {
    servo.write(normalpos);
    // servo shaft angle for release brake.
    digitalWrite(relay, LOW);
    // To reconnect motor supply
  }
}
long radar(void)
{
  digitalWrite(trig, HIGH);
  delayMicroseconds(15);
  digitalWrite(trig, LOW);
  long  dur = pulseIn(echo, HIGH);
  dur = dur / 58;
  return dur;
}