automatons
WHAT IS A ROBOTThe 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
TRICYCLE
FOUR WHEELED DRIVE
TRACKED PLATFORMS
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 anexternal 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 lookLoad bearing and stiffDoes 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 anydirection 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 ADVICEMechanic 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 PORTDC and stepper motor introductionInterfacing to motors and sensors
MOTOR INTERFACING METHODSDC motorsStepper 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 REPRESENTATIONSIGNAL REPRESENTATION AND BOOLEAN LOGICAND BOOLEAN LOGIC
Boolean logic is a branch of study that deals with quantitiesBoolean logic is a branch of study that deals with quantities represented by either yes(1) or no(0).represented by either yes(1) or no(0).
All decimal numbers can be broken down to digital numbers by using All decimal numbers can be broken down to digital numbers by using base 2 computation. base 2 computation.
In terms of voltages we assign 5V as logic 1 and 0V as logic 0 in In terms of voltages we assign 5V as logic 1 and 0V as logic 0 in digital electronics.digital electronics.
THE PRINTER PORTTHE PRINTER PORT
The printer port is a 25 pin female connector found on most The printer port is a 25 pin female connector found on most modern computers.modern computers.
It is possible to command the printer port to set (1)or reset (0)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 arecertain pins by writing a program on the computer. Such pins arecalled output pinscalled output pins
It is also possible to read the value of certain pins on the port and 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 pinsthese 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) toSo if we configure the motors to be connected (via a motor driver) tothe output pins and sensors to input pins, and use a certain logic tothe output pins and sensors to input pins, and use a certain logic tocontrol the motors depending on the sensor values, it is possible to control the motors depending on the sensor values, it is possible to control a robot whose parts are those sensors and motors.control a robot whose parts are those sensors and motors.
THE PRINTER PORT PINSTHE PRINTER PORT PINS
OUTPUTTING VALUES FROM THE PORTOUTPUTTING VALUES FROM THE PORT
The data port is used as the output port.The data port is used as the output port.
The address of the data port is 0x378(base) on most computers.The address of the data port is 0x378(base) on most computers.
In C if a command likeIn C if a command like
Outportb(0x378,4); // base=0x378Outportb(0x378,4); // base=0x378
Is executed then the value of data port pins will beIs executed then the value of data port pins will be
(0 0 0 0 0 1 0 0) // binary for 4(0 0 0 0 0 1 0 0) // binary for 4
INPUTTING VALUES FROM THE PORTINPUTTING VALUES FROM THE PORT
There are two input ports on the printer portThere are two input ports on the printer portstatus port (base+1) and control port (base+2)status port (base+1) and control port (base+2)
Both have less than 8 pins as inputs and have to be Both have less than 8 pins as inputs and have to be used in conjunction for more inputs (upto 8)used in conjunction for more inputs (upto 8)
A statement like A statement like
int c;int c;c=inportb(0x379); // 0x379=base+1c=inportb(0x379); // 0x379=base+1
Will read the status port and store the read value in Will read the status port and store the read value in variable cvariable c
DRIVING MOTORSDRIVING MOTORS The H-bridgeThe H-bridge
The H-bridge is a transistor based circuit that can input digital The H-bridge is a transistor based circuit that can input digital logic value and switch a connected motor clockwise or anticlockwise.logic value and switch a connected motor clockwise or anticlockwise.
If switches A and D are on then current flow from the supply ,If switches A and D are on then current flow from the supply ,Switch A ,coil, switch D and ground.Switch A ,coil, switch D and ground.
If switches B and C are on then current flow from the supply ,If switches B and C are on then current flow from the supply ,Switch B ,coil, switch C and ground.Switch B ,coil, switch C and ground.
THE L293 AND L298THE L293 AND L298
Both these integrated circuits are two H-bridges in a single package.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 They have 4 signal inputs that select witch transistor is on and 4 output pins to which we connect motorsoutput pins to which we connect motors
Other pins include digital power, motor power, GND pins, inhibit Other pins include digital power, motor power, GND pins, inhibit pins and current limit pins.pins and current limit pins.
L293 is available in DIP package so has a rating of 1 AMP for bothL293 is available in DIP package so has a rating of 1 AMP for both bridges collectively.bridges collectively.
The L298 is a beefy version and can have a total rating of 2 AMPS withThe L298 is a beefy version and can have a total rating of 2 AMPS with a heat sink to be connected externally.a heat sink to be connected externally.
L298L298
STEPPER MOTORSSTEPPER MOTORS
TYPES OF STEPPER MOTORSTYPES OF STEPPER MOTORS Unipolar Motors(5 Wire Or 6 Wire)Unipolar Motors(5 Wire Or 6 Wire)
Bipolar Motors(4 Wire)Bipolar Motors(4 Wire)
All the above motors just about have the same internal windings All the above motors just about have the same internal windings but the difference come in the way they are drivenbut the difference come in the way they are driven
Unipolar motors can be driven by either discrete transistors or H Unipolar motors can be driven by either discrete transistors or H bridgesbridges
Bipolar motors are exclusively driven by H-bridgesBipolar motors are exclusively driven by H-bridges
A stepper motor has four phase windings named A stepper motor has four phase windings named A B C D A B C D
When a phase is excited it means that thatWhen a phase is excited it means that thatphase has current flowing through itphase has current flowing through it
A particular phase sequence imparts rotationA particular phase sequence imparts rotation to the motorto the motor
The two excitation sequences areThe two excitation sequences are
HALF WAVE AND FULL WAVEHALF WAVE AND FULL WAVE
HALF WAVE EXCITATIONHALF WAVE EXCITATION
The phase sequence for a particular direction of rotation isThe phase sequence for a particular direction of rotation isA-B-C-D-A-B-C-D-A-B …………A-B-C-D-A-B-C-D-A-B …………
To reverse the direction of rotation the sequence isTo reverse the direction of rotation the sequence isD-C-B-A-D-C-B-A ……..D-C-B-A-D-C-B-A ……..
FULL WAVE EXCITATIONFULL WAVE EXCITATION
The phase sequence for a particular direction of rotation isThe phase sequence for a particular direction of rotation isA- AB- B- BC- C- CD- D- DA- ……A- AB- B- BC- C- CD- D- DA- ……
To reverse the direction of rotation the sequence isTo reverse the direction of rotation the sequence isD- CD- C- BC- B- AB- A- ……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 usingPulse 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
ROBOT CONTROL USING PRINTER PORT
LOOKING BACK
MICROPROCESSORS ANDMICROCONTROLLERS
A microprocessor is a device that does sequencing of instruction that is written to its associated memory.
A microcontroller is same as a microprocessor but has its memory and other peripherals associated with it in a single IC package.
We will concentrate on microcontrollers but will dwell a little bit into microprocessors.Example 8085
COMMON MICROCONTROLLER FAMILIES
8051
First microcontroller to be launched.
Very used and hence lots of programming resources.
8051 derivatives are also available with multiple Features.
Not a good choice for robotics applications.
Messy programming interface.
Still in use today for embedded applications.
PIC-PERIPHERAL INTERFACE CONTROLLER
Good microcontroller family
Programming resources also available
Programmer mode is ICSP (In Circuit Serial Programmer)One programmer fits all devices
Available in variety of cost and features
Suited for small robotic applications.
Never used it !!!
FEATURES OF ATMEGA85358 bit microcontroller with RISC architecture
On board 10 bit 8 channel ADC with highest sampling upto15 kHz
Onboard UART with independent receive and transmit registers
4 ports with high drive capability
8kb of on chip flash memory with ISP programmability
One programmer fits all devices
512 byte of SRAM and 512 bytes of EEPROM
3 timers with PWM function
PROGRAMMER SCHEMATIC FOR AVR
BATTERY TECHNOLOGY
OPTIONS FOR BATTERIES
SEALED LEAD ACID OR SLA BATTERIES
Ni-Cd BATTERIES
Ni-MH BATTERIES
CELL CHARACTERSTICS
VOLTAGEREGULATORS
These are three pin devices whose output voltage is approximately a constant over a large range of input conditions.
The 78XX series of voltage regulators is popular. The XX stands for the output voltage that a certain device will deliver. For e.g.
A 7805 voltage regulator will deliver output voltage at 5 volts.
These devices at least need input voltage about 2 volts higher than the output.
A 7805 regulator is required to provide constant voltage for logic circuitry.
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