WHAT IS A ROBOT The Three Laws Of Robotics (ISAAC ASIMOV) A robot may not injure a human being, or, through inaction, allow a human being to come to harm. A robot must obey the orders given it by human beings except where such orders would conflict with the First Law. A robot must protect its own existence as long as such protection does not conflict with the First or Second Law.
An autonomous robot is simply a self-contained robot that receives no assistance from outside, not even power. WHAT IS AN AUTONOMOUS ROBOT
THE BUILDING BLOCKS OF A ROBOT Mechanical Blocks Electronics Computer Code Or Firmware Intelligence Shall we start
CHASSIS DESIGN ACTUATORS MOTORS-DC AND STEPPERS WHEELS CASTORS MATERIALS FOR CHASSIS DESIGN AND TOOLS WEIGHT AND POWER CONSIDERATIONS BUILDING SMALL ROBOTS
CHASSIS DESIGN TRICYCLE FOUR WHEELED DRIVE TRACKED PLATFORMS
FOUR WHEELED DRIVE
ACTUATORS An actuator is a transducer that will convert one form of energy to mechanical movement. For example a motor, hydraulic cylinders, solenoids etc
MOTORS A motor converts electrical energy to rotational movement. TYPES OF MOTORS USEFUL FOR A ROBOT DC MOTORS STEPPER MOTORS
Consists of two wires externally. Turn clockwise or anticlockwise when either wire is at a higher potential than the other. Normally have to be geared to provide working torque. Robots that work autonomously should restrict speeds over 100 rpm for driving motors. More In The Electronics' Part Of Dc Motors
These are motors that rotate in steps up on an external command. Excellent when accurate positioning is required. Have very minimal torque and hence design of the robot becomes critical But are a good alternative to DC motors They can consume larger currents as compared to DC motors of comparable sizes. More In The Electronics' Part Of Steppers..
The next most important part of the robot is its wheels. Wheels determine the pulling force of the robot, its speed, and actually its height. A back of the hand formula is that the larger the wheel the lower the available force and higher the speed. Select the lowest possible wheel diameter for the task at hand
The simple calculation comes from the torque formula F=r x T So a larger wheel calculates to a high speed but a low pulling force
WHEEL MATERIALS Aluminium Advantages Looks very professional and robot looks neat. Highly load bearing and stiff Does not get corroded easily and will not sag or swell like wood. Disadvantages A little bit expensive but wheels last long. Slightly difficult to work with and hence have to be machined (actually bad when things fall off on last day) Slightly heavy and have to be spoked to reduce weight.
NYLON Advantages Gives a clean look Load bearing and stiff Does not get corroded easily and will not sag or swell like wood. Affordable and light weight. Has to be machined
WOOD Absolute no no!!
CASTORS A castor is a free wheel that can rotate in any direction in one plane A castor is a wheel that normally attached to trolleys, cabinets etc. Such a wheel provides a third point of balance in tricycle type chassis and turns in any direction thus allowing smooth turns
MATERIALS FOR CHASSIS DESIGN ALUMINIUM Available in various cross sections. Can be easily visualised in the requisite shape. But can be time consuming and demanding to cut, drill and bend. Chassis is very lightweight and durable.
ACRYLIC Available in sheets of various thickness and sizes. Can be cut, drilled very easily. Cheap material for good design. Brittle and not very strong. Leaves irritating shavings after work.
TOOLS Hacksaw for both wood and metal. Small bench vice. Hand drill with standard bit sizes. Other tools like hammer, pliers ,spanners etc
BUILDING SMALL ROBOTS All devices are miniaturised Motors are available in small sizes
SOME ADVICE Mechanic assemblies are a one time investment Build and machine good wheels and a stiff chassis The best design is a two motor configuration with two castors as front wheels Choose the smallest diameter possible. The alignment should be very accurate and the robot should not be correcting itself every time because of misalignment. Motors have to be dead straight. Always this is achieved by a professional turner. Weight of the robot should be as low as possible.
SIGNAL REPRESENTATION,BOOLEAN LOGIC THE PRINTER PORT DC and stepper motor introduction Interfacing to motors and sensors MOTOR INTERFACING METHODS DC motors Stepper Motors SENSORS AND CONFIGURATIONS
Programmable Devices Using Embedded Devices-Processors And Controllers Introduction To Devices And Design The Common Controller Families-8051, PIC And AVR The ATMEGA8535-Controller For Robotic Applications Features Of This Device And Peripherals Interfacing To Motors And Sensors Battery Technology And Regulators
SIGNAL REPRESENTATION AND BOOLEAN LOGIC Boolean logic is a branch of study that deals with quantities represented by either yes(1) or no(0). All decimal numbers can be broken down to digital numbers by using base 2 computation. In terms of voltages we assign 5V as logic 1 and 0V as logic 0 in digital electronics.
THE PRINTER PORT The printer port is a 25 pin female connector found on most modern computers. It is possible to command the printer port to set (1)or reset (0) certain pins by writing a program on the computer. Such pins are called output pins It is also possible to read the value of certain pins on the port and these can also be read by program. Such pins are called input pins So if we configure the motors to be connected (via a motor driver) to the output pins and sensors to input pins, and use a certain logic to control the motors depending on the sensor values, it is possible to control a robot whose parts are those sensors and motors.
THE PRINTER PORT PINS
OUTPUTTING VALUES FROM THE PORT The data port is used as the output port. The address of the data port is 0x378(base) on most computers. In C if a command like Outportb(0x378,4); // base=0x378 Is executed then the value of data port pins will be (0 0 0 0 0 1 0 0) // binary for 4
INPUTTING VALUES FROM THE PORT There are two input ports on the printer port status port (base+1) and control port (base+2) Both have less than 8 pins as inputs and have to be used in conjunction for more inputs (upto 8) A statement like int c; c=inportb(0x379); // 0x379=base+1 Will read the status port and store the read value in variable c
DRIVING MOTORS The H-bridge The H-bridge is a transistor based circuit that can input digital logic value and switch a connected motor clockwise or anticlockwise.
If switches A and D are on then current flow from the supply , Switch A ,coil, switch D and ground. If switches B and C are on then current flow from the supply , Switch B ,coil, switch C and ground.
THE L293 AND L298 Both these integrated circuits are two H-bridges in a single package. They have 4 signal inputs that select witch transistor is on and 4 output pins to which we connect motors Other pins include digital power, motor power, GND pins, inhibit pins and current limit pins. L293 is available in DIP package so has a rating of 1 AMP for both bridges collectively. The L298 is a beefy version and can have a total rating of 2 AMPS with a heat sink to be connected externally.
STEPPER MOTORS TYPES OF STEPPER MOTORS Unipolar Motors(5 Wire Or 6 Wire) Bipolar Motors(4 Wire) All the above motors just about have the same internal windings but the difference come in the way they are driven Unipolar motors can be driven by either discrete transistors or H bridges Bipolar motors are exclusively driven by H-bridges
A stepper motor has four phase windings named A B C D When a phase is excited it means that that phase has current flowing through it A particular phase sequence imparts rotation to the motor The two excitation sequences are HALF WAVE AND FULL WAVE
HALF WAVE EXCITATION The phase sequence for a particular direction of rotation is A-B-C-D-A-B-C-D-A-B To reverse the direction of rotation the sequence is D-C-B-A-D-C-B-A .. FULL WAVE EXCITATION The phase sequence for a particular direction of rotation is A- AB- B- BC- C- CD- D- DA- To reverse the direction of rotation the sequence is D- CD- C- BC- B- AB- A-
The ULN2803 This is an IC that contains 8 Darlington's with diode protection This is used to control only an unipolar stepper motor It is rated for 500mA and 36 V. The cheapest solution to drive a stepper motor. Every phase has to be individually set or reset.
UCN 5804 This IC has in built logic to drive an unipolar stepper motor. The only inputs that are required are clock, direction and whether the excitation is full or half wave. Expensive.
SPEED CONTROL OF MOTORS DC MOTORS Speeds of dc motors can be controlled by using Pulse width modulation or PWM STEPPER MOTORS Speed control can be done by changing the time Interval between two successive steps.
SENSOR INTERFACING The types of sensors are Active and Passive Depending on the type the configuration of the sensor changes For passive sensors the most common configuration is of a potential divider.
LIGHT SENSORS INFRARED SENSORS These are two pin devices available in pairs-transmitter and receiver the transmitter is forward biased and the receiver is reversed biased. When the receiver is irradiated with infrared light its resistance decreases. PHOTOTRANSISTORS These are three pin devices of which only two pins are used . The configuration is same but this sensor is blind to infrared light It has sensitivity to visible light