robotics-a+beginners+guide

7/21/2019 ROBOTICS-A+beginners+guide

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The word robotics is used to collectively define afield in engineering that covers the mimicking ofvarious human characteristicsSound concepts in many engineering disciplines isneeded for working in this particular field

It finds its uses in all aspects of our life


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An automatic industrial machine replacing thehuman in hazardous work

An automatic mobile sweeper machine at amodern homeAn automatic toy car for a child to play with

A machine removing mines in a war field all byitself and many more


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Here we are aiming at design and prototyping ofmobile robots capable of controlled locomotion.It may be via human or automatic control.Here we aim to make a bot capable of traversing awhite line on a black surface automatically.It must be able to perform certain tasks we set for it.

The task must be achieved within some givenlimitations.Keeping this as the basic idea we will be able tofurther widen our applications


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Locomotion system

Power supply system

ActuatorsSensory devices for feedback

Sensor Data processing unit

Control system


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As the name suggests a mobile robot must have asystem to make it move

This system gives our machine the ability to moveforward, backward and take turnsIt may also provide for climbing up and down


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A simple equation: Power is the product of Torqueand Angular velocity

P = X This implies that if we want more torque (pullingcapacity) from the same motor we may have tosacrifice speed and vice versa


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The dc motors (tape motors) available have veryhigh speed of rotation which is generally notneeded. But what they lack is torque outputFor reduction in speed and increase in pullingcapacity we use pulley or gear systems

These are governed by: 1 X r1 = 2 X r2The above concept will be discussed shortly


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They convert the electrical energy into meaningfulmechanical work

Mechanical output can be rotational or linear(straight line)Motors provide rotational motion

Electromagnets provide linear motion


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AC Motors : Not used much in robotics

DC Motors : Finds extensive general use

Stepper Motors : For controlled rotationServo Motors : For controlled rotation


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As the name suggests, a motor which uses aDC (Direct Current) power

Can run in both directionsSpeed ControllableDirection of rotation controlled by polarity of

current / voltageSpeed of rotation controlled by averageenergy (power) fed to the motor


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The motors we use in makingdifferential drive are simple DCmotors.


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Direction of rotation controlled by polarity ofcurrent / voltageSpeed of rotation controlled by average energy(power) fed to the motor


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Operating Voltage : Recommended voltage forpowering the motor

Operating Current : Current drawn at a certain loadon the shaft

Stall Current : Maximum current drawn, whenmotor not allowed to rotateStall Torque : Rotation force needed to hold themotor in stall condition


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Free running torque & current are ideally zero

Increased load implies, increased torque, current

drawn & power consumptionPower supplied by a motor is the product ofoutput shafts rotational velocity & torque

DC Motors are high speed, low-torque devices

Using gears, the high speed of the motor istraded off into torque


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Zero speed atmaximum load (stall

torque)Highest speed whilefree running (zeroload)

Highest power at halfspeed & half load


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This is the car type drive and themost common in real world butnot in robot world as inautomobiles.

The translation and rotation areindependent of each other. But

translation and rotation areinterlinked hence this system facessevere path planning problem


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A close relative of the differential drive systemIt is mostly used in tracked machines e.g. tanks.Also finds application in some four / six wheeledrobotsThe left and right wheels are driven independentlySteering is accomplished by actuating each side at

a different rate or in a different direction, causingthe wheels or tracks to slip, or skid, on the ground


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In this mechanism the machine chassis (body) isdeformed to achieve rotation in contrast to thesteering wheels in car type drive


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It is made up of a system of motors. One set ofwhich drive the wheels and the other set turns thewheels in a synchronous fashion


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The most unique type of Locomotion system

It is composed of a four wheeled chassis and aplatform that can be raised or lowered


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A differential drive is the most basic drive,which consists of two sets of wheels that can

be driven independently.By using different movements of the right and left wheels it is

possible to make the robotmove forward, backwards,right, left and even for zero degree turns.


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Simplicity and ease of use makes it the mostpreferred system by beginnersIndependent drives makes it difficult for straightline motion. The differences in motors andfrictional profile of the two wheels cause them tomove with slight turning effectThe above drawback must be countered withappropriate feedback system. Suitable for humancontrolled remote robots


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Our power supply consists of the rectifier circuitand the transformer.

The transformer is used to step down voltagefrom220 volt AC to 12 volt AC( or any other desiredvalue).

Further the rectifier converts 12v AC to 12v DCsupply.


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A transformer is a device that transfers electrical

energy from one circuit to another throughinductively coupled conductors.

To make a simple differential drive, a simple

transformer with following specifications can beused:

1 Amp , C.T. 12 V.( it steps down a 220V AC to 12 VAC.


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220 V ACsupply

12VAC

-12VAC


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A rectifier is an electrical device thatconverts alternating current (AC), current thatperiodically reverses direction, to directcurrent (DC), current that flows in only onedirection.


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Electrolytic Capacitor

Integrated circuit (IC 78XX)

pside

nside

1N4001 pn junction diode

+

-


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Most electrolytic capacitors are polarized, i.e., theyhave a positive and negative terminal. Connectingthem to wrong terminals of power supply candestroy it. Adding to this, these capacitors are usedonly for DC voltages.

Fig: A blown capacitor


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These ICs are voltage regulator integrated circuits.The voltage regulator IC maintains the outputvoltage at a constant value. The xx in 78xxindicates the fixed output voltage it is designed toprovide. 7805 provides +5V regulated powersupply. Similarly there are several other ICs

available in this category like 7806, 7809, 7812,7815.


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Another fact to note about this series of ICs is thatthey have a voltage range in which they work. Forany voltage above that range the IC goes into athermal shutdown and will give you a very lowarbitrary voltage value. For example, the 7805 IChas a range between 5V and 16V.


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These are current amplifying circuitsA low current control signal is converted into aproportionally higher current signal that candrive the motor

Power Transistors can switch high currents. TheICmax is usually of the order of Amps ascompared to small signal transistors which haveICmax in mA


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H Bridge Circuit Diagram

S 1

S 3

S 2

S 4

M1 2

V CC


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L293D Pin Diagram


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It is an electronic circuit which enables a voltage tobe applied across a load in either direction.

It allows a circuit full control over a standardelectric DC motor. That is, with an H-bridge, amicrocontroller, logic chip, or remote control canelectronically command the motor to go forward,

reverse, brake, and coast.


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H-bridges are available as integrated circuits, orcan be built from discrete components.

The term "H-bridge" is derived from the typicalgraphical representation of such a circuit, which isbuilt with four switches, either solid-state (eg,L293/ L298) or mechanical (eg, relays).


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The current provided by the MCU is of the order of5mA and that required by a motor is ~500mA.Hence, motor cant be controlled directly by MCU

and we need an interface between the MCU and themotor.

A Motor Driver IC like L293D or L298 is used for thispurpose which has two H-bridge drivers. Hence,each IC can drive two motors


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Note that a motor driver does not amplify thecurrent; it only acts as a switch (An H bridge isnothing but 4 switches).


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Analogous to human sensory organs

Eyes, ears, nose, tongue, skin

Sensors help the robot knowing itssurroundings better

Improves its actions and decision making

abilityProvides feedback control


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Made of cadmiumsulphide

Resistance between twoterminals varydepending on theintensity of light

Can be used todifferentiate contrastcolours


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LM339, LM393 and LM311

They consist of more than one comparator.

LM311 consists of single comparator


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Light Sensing Module using LED-LDR combination


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A line follower is a robotcapable of tracking a linedrawn on a surface

Optical sensors capturethe line position at thefront end of the robot

The robot is steered tokeep it always over theline


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All the sensors are assignedsome weight such as

Sensor 1 = a1 = 3Sensor 2 = a2 = 2

Sensor 3 = a3 = 1

Sensor 4 = a4 = -1Sensor 5 = a5 = -2

Sensor 6 = a6 = -3


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Robosoccer is the in house event of Robotix whereteams of three make differential drive robots andparticipate in a one-on-one football match.


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The chassis (and the wheels) can simply be cut out

from the toycars easily available in the market by

separating the lower part of the car from the upperone and removing the gear box from it.

For more details, please refer to the link:

http://www.youtube.com/watch?v=kFoGBIqIqoMHAPPY BOT MAKING!!!
http://www.youtube.com/watch?v=kFoGBIqIqoMhttp://www.youtube.com/watch?v=kFoGBIqIqoM


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THANK YOU

robotics-a+beginners+guide

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