Objective: To build a robot with the parts available at your home. I always wanted to build a robot on my own. So how to start! I did a lot of research by gaining knowledge on robotics, sensors and microcontroller; www.societyofrobots.com is one of my favorite sites, which helped me to understand the basics of building robots and I am glad to be a part of this society today. I wanted to share my experience of building my first robot with you all.
Description: Since I am a beginner I wanted to start with the basic stuff. First the microcontroller: In my learning I have seen people always talking about three microcontrollers for programming the robots; BASIC Stamp, PIC and ATMega; I went for BASIC Stamp which is readily available in Radio Shack which comes with great electronics like servos, LED’s, jumper cables, switches and reading material. The material is very helpful and explains how each electronic part works along with the diagram, a simple code in BASIC programming language. I was able to go through all the chapters within a week and was able to successfully complete all the projects given in the book. I got an idea about the sensors, servos etc and it is time for me to put this into test. As my first task I thought of building an unmanned vehicle with the help of sensors and servos.
The Base: After searching for a base for my vehicle I decided to use my old DVD (non-workable) player case. I had to dismantle all its parts to detach the base along. I attached two servos to the front side (one on either side) of the base after cutting it in proper dimension. I am not a CAD user hence I used a ruler and approximation to cut them with the help of a normal kitchen knife. I do not want to use another set of servos at the back and hence attached a small wheel taken from the wheel chair. This wheel helps the robot to turn freely. Now this becomes a 3-wheeled robot. I attached a third servo, which is a standard servo (standard servo – rotates 180 degrees and continuous servo – rotates continuously) to the front-middle of the base and attached an ‘L’- shaped plastic to the top, the ultrasonic sensor will fit into this ‘L’ shaped plastic. This now acts as the eye for this robot and rotates 180 degrees looking forward. This was the most exciting moment of this project J
How it works: When the battery is on, the microcontroller signals the two servo motor to rotate forward and also signals the ultrasonic sensor to scan for objects at the front. If the sensor finds an object within say ‘x’ meters it signals back the microcontroller to stop the robot. Now it signals the standard servo to rotate both directions to measure the distance with the help of the sensor. The two values are then compared and the greatest of them is chosen. If the left side has the greatest it means the robot can now go towards the left and vice versa. The controller then instructs the robot to move in that direction. I am using the simple differential drive algorithm where if the robot wants to move towards left, it stops the left side servo and rotates the right-hand side servo forward, this will enable the robot to turn left and vice versa. This continues until I remove the battery from the microcontroller of the battery drains completely.
Parts:
BASIC Stamp Microcontroller: 1 $80 from Radio shack
1 Standard servo: comes with the BASIC Stamp kit
2 Continuous rotation Servo: $13 each (I had to order online)
1 DVD case for the base
2 wheels from my old toy car
1 wheel taken from the wheel chair (for the rear wheel)
1 L shaped plastic taken from the CPU monitor screen
Necessary tools for cutting and drilling holes
1 9V battery for the BASIC Stamp
Programming Language used:
I used the BASIC programming language for this as the compiler comes with the package. You can also program this in C or any other language you are familiar with but BASIC is very easy and I recommend for the beginners using BASIC Stamp microcontroller. Some people also build their own microcontroller circuit which I do not want to because my aim was to build a robot and not programming the microcontroller. Here is the source code for my robot. It took me around 3 months to study about the robotics and come up with this robot.
' {$STAMP BS2}
' {$PBASIC 2.5}
'Author : vijay narayan
'Date Created : 6/28/07
'Date Modified : 7/3/07
'Purpose: Robot program to simulate unmanned vehicle
'---minimum pulse duration for clockwise-most---
RIGHTMOST VAR Word
'---minimum pulse duration for anti-clockwise-most---
LEFTMOST VAR Word
'---center pulse duration---
CENTER VAR Word
'---pause duration---
PAUSE_DURATION VAR Word ' the smaller the value, the smoother the turn
'---used for loop variant---
i VAR Word
'---keep track of current position---
CURRENT_POSITION VAR Word
'---the step for the turning---
ROTATION_STEP VAR Word
'**********initialize the values**********
RIGHTMOST = 200'190
LEFTMOST = 1100'1180
CENTER = 650
PAUSE_DURATION = 10 ' the bigger the value, the slower it is
CURRENT_POSITION = CENTER ' always turn to the center point
ROTATION_STEP = 20 ' the bigger the value, the more it turns
'SCANNING_STEP = 1 ' the bigger the value, the faster it scans
'***********************************
LeftInch VAR Word
RightInch VAR Word
'Constants for pins
RightWheel CON 15
LeftWheel CON 13
CenterWheel CON 11
USSensor CON 3
'Variables
rawDist VAR Word
inches VAR Word
cm VAR Word
Counter VAR Byte
'Starting routine
GOSUB
'This will ping the Ultrasonic when the sensor is pointing to the left side
PINGSensorOnLeft:
FOR Counter = 1 TO 10
LOW USSensor
PULSOUT USSensor,1
PULSIN USSensor,1,rawDist
rawDist = rawDist * 10
rawDist = rawDist / 2
LeftInch = rawDist ** 889
DEBUG HOME, "left inchs ", DEC LeftInch, CR
PAUSE 100
NEXT
DEBUG HOME, "Final left inchs ", DEC LeftInch, CR
RETURN
'This will ping the Ultrasonic when the sensor is poining to the right side
PINGSensorOnRight:
FOR Counter = 1 TO 10
LOW USSensor
PULSOUT USSensor,1
PULSIN USSensor,1,rawDist
rawDist = rawDist * 10
rawDist = rawDist / 2
RightInch = rawDist ** 889
DEBUG HOME, "right inchs ", DEC RightInch, CR
PAUSE 100
NEXT
DEBUG HOME, "Final right inchs ", DEC RightInch, CR
RETURN
'This will ping the Ultrasonic when the sensor stand is center
PINGSensor:
LOW USSensor
PULSOUT USSensor,1
PULSIN USSensor,1,rawDist
PULSOUT RightWheel,1000
PULSOUT LeftWheel,500
rawDist = rawDist * 10
rawDist = rawDist / 2
inches = rawDist ** 889
cm = rawDist ** 2257
DEBUG HOME, "inchs ", DEC inches, CR
RETURN
'Entry point of the program
'This function would mak the robot move forward and check for the distance
GOSUB Centralize
DO
GOSUB PINGSensor
IF inches <= 70 THEN
GOSUB Scan
'GOSUB MoveReverse
'GOSUB MoveLeft
'GOSUB MoveRight
ENDIF
' DEBUG HOME, "cm ", DEC cm,CR
PAUSE 20
RETURN 'end of Main function
'This function would step the robot back wards
MoveReverse:
' LOW USSensor
' PULSOUT USSensor,0
FOR Counter = 1 TO 10
PULSOUT RightWheel,500
PULSOUT LeftWheel,1000
PAUSE 100
NEXT
RETURN
'Differential Move algorithm
'Function to make the robot move left
MoveLeft:
DEBUG HOME, "Move left ", CR
FOR Counter = 1 TO 46
PULSOUT RightWheel,0
PULSOUT LeftWheel,500
PAUSE 50
NEXT
RETURN
'Function to make the robot move right
MoveRight:
DEBUG HOME, "Move right ", CR
FOR Counter = 1 TO 46
PULSOUT RightWheel,1000
PULSOUT LeftWheel,0
PAUSE 50
NEXT
RETURN
'Function to scan from left to right and vice versa
Scan:
'At the time of scan we dont want the
LOW USSensor
PULSOUT USSensor,0
FOR i = CURRENT_POSITION TO LEFTMOST 'STEP SCANNING_STEP
PULSOUT CenterWheel, i
CURRENT_POSITION = i
PAUSE PAUSE_DURATION
NEXT
'Now measure the distance at this point
GOSUB PINGSensorOnLeft
LOW USSensor
PULSOUT USSensor,0
FOR i = CURRENT_POSITION TO RIGHTMOST 'STEP SCANNING_STEP
PULSOUT CenterWheel, i
CURRENT_POSITION = i
PAUSE PAUSE_DURATION
NEXT
'Now measure the distance at this point
GOSUB PINGSensorOnRight
'Compare between the distance
IF LeftInch > RightInch THEN
GOSUB Centralize
GOSUB MoveLeft
'ELSEIF LeftInch < RightInch THEN
ELSE
GOSUB Centralize
GOSUB MoveRight
ENDIF
RETURN
'function to bring back the central motor to the center
Centralize:
FOR i = 1 TO 40
PULSOUT CenterWheel, CENTER
PAUSE PAUSE_DURATION
NEXT
CURRENT_POSITION = CENTER
RETURN
Pictures:
I did not realize that I had to take pictures of the parts that I used for building this robot at the time of the design but I would like to share the video.
http://www.youtube.com/watch?v=AVghsPP_Rn4
Conclusion: This is my first project and I am really glad that I was able to complete this successfully. I am looking forward to build more robots in future and would be sharing my experience with you all. Thanks for your time in reading this and expect to drop your comments.
Keep building Robots and Have fun!