WEEK 2

PREFACE TO WORK 

An active tactile sensor which  is going to mount on the mobile robot,   is an antenna  that can be used to detect the obstacles and identify their materiel , the distance from the robot and  the shape.  Since the model is independent of lighting  condition, it can be use without any light source  to track the paths . Accelerator is the only sensor which is mounted on top of the antenna  . The antenna is able to detect the  acceleration which is happen due to some contact and by analyzing that data  the system is able to  identify the material and shape of the object. 

PROGRESS

Continue the  study of reading materials.  According to the reading materials a proper data set is needed to go for analyzing process of the project.  Therefore mainly focus on the collecting data set.    

Initial accelerator and pan tilt unit  testing  were started.  Two MR RC 1503 servo motors were used to design prototype pan tilt unit and it was controlled by using raspberry pi 3 development board and the PCA 9685 servo controller.Initially the servo motors were controlled without using the PCA9685. In that case studied the behavior of the servo motors to set the PWM (Pulse Width Modulation) signal to the motors.  Specification details of the used motors as follows.

• Brand: MR.RC

• Stall torque: 4kg/cm (4.8V), 6kg/cm (6.0V)

• Operating voltage: 3.5-8.4V 

• Operating speed: 0.14sec/60°at 4.8v, 0.11sec/60°at 6v

• Cable length: 300mm

• Weight: 47g

if it is used a micro controller which has a PWM   out put like (ARDUINO) it is very much easy to control the motors.  But the controlling boards like Raspberry doesn't have a PWM pin it self. Therefore we need to have manually  calculate the pulse for the PWM signals.

CALCULATIONS

Figure 01: Calculations for the servo motor PWM signal

CODE

import RPi.GPIO as GPIO

import time

GPIO.setmode(GPIO.BOARD)

GPIO.setwarnings(False)

GPIO.setup(11, GPIO.OUT)

GPIO.setup(12, GPIO.OUT)

p = GPIO.PWM(11, 50)

q = GPIO.PWM(12, 50)

p.start(7.5)

q.start(7.5)

try:

        while True:

                p.ChangeDutyCycle(2.5)

                q.ChangeDutyCycle(2.5)  # turn towards 0 degree

                time.sleep(1) # sleep 1 second

                p.ChangeDutyCycle(12.5)

                q.ChangeDutyCycle(12.5) # turn towards 180 degree

                time.sleep(1) # sleep 1 second 

except KeyboardInterrupt:

 p.stop()

GPIO.cleanup()

The following video shows how  the prototype unit of the pan tilt works at the initial state. 

REFERENCE