How to build a tracked robot ?

If there is a design that combines speed ,power ,maneuverability,control thats track drive.You must have seen this design in a battle tank ,bull dozer and lots of off road vehicles .
Click on this picture to enlarge


Basically this kind of drive can be imagined as a vehicle that lays a track for itself as it moves.
And don't get tensed we are not going to build anything this complicated.
PRESSURE STUFF
So what this basically does is spreads out the weight evenly,as a result more traxion.Consider this example For instance, the ground pressure of a car which may weigh a tonne is equal to the pressure of the air in the tires, perhaps 30 psi (207 kPa), whereas the seventy-tonne M1 Abrams tank has a ground pressure of just over 15 psi (103 kPa).(amazing isn't it ).So as the ground pressure is less the vehicle rarely gets stuck when it goes off road .Well how are we going to build a robot like this ......Lets see.
LETS BUILD
First consider the size of your robot and choose a rubber belt according to the size of your robot.The belts come in varying shapes and sizes.Small like this one


If you want to make a bigger bot you can go for industrial belts with custom made sprockets and boogie wheels .I know a place in Chennai where you get those belts .I'll put the address in a few days.This is the industrial belt available.

MACHINING SPROCKETS AND BOGIE WHEELS
Sprockets can be machined from poly carbonate rods available commercially .And the machining process is normal like machining a metal and the same tools can be used .
BUILDING THE CHASSIS
The chassis can be built by conventional methods by using a plywood ,sheet metal or u can build your own chassis by welding metal pipes or flat rods.
STEERING
The tank uses a differential steering mechanism.
These are the pictures of bots which have used the same materials that I mentioned .Take a look at it.


The first one had used a plywood base and second one a sheet metal..
So start building good luck:) !!!!!!!

How to build a sumo robot ?

How to build a sumo robot ?
Sumo wrestling is an interesting and thrilling event and it has a history and tradition behind it.Basically it may be held as an autonomous or wireless controlled event.So lets see the basics of building a SUMO robot.
CHOOSING A MOTOR
First deceide the motor you are going to use.Speed is inversely proportional to torque.So go for a slow speed motor that gives good torque.And then start building the chassis click here ---> > for more mechanical designs and ideas.
STEERING MECHANISM
Then build your chassis .And deceide the steering mechanism that you are going to use.Always go for differential steering than ackerman steering mechanism.Differential steering provides more manuverablity and easy control which is crucial.Incase you dont know what differential steering mechanism is I will explain you with the following diagram .



I'll explain you the steering mechanism

Both motors forward bot moves forward . If left motor is switched off or reversed bot and right motor is forwarded turns towards left ..and the other way for the right turn.This is very basic and most people know it.
INTERFACING RADIO CONTROL
Then you have to choose a radio control kit.it is always better to have two kits to avoid frequency interference.You can use RC kits stripped from old cars .Then you will have to use the signal from the receiver and drive your motors.If your are using big motors do not use the receicer to drive the motor directly .you might fry it.So you have to make a driver to drive the motor.A H bridge is usually used to drive the motor, relays can also be used.If you use relays you need not worry about voltage and current ratings of motor.
VERY VERSATILE H BRIDGE


Click on the image to see clearly .

This is a very versatile H bridge circuit.And D88O is a power transistor having a max current range of 3 A and voltage range more than 50 v and more amazing is is that it costs only 4 rupees in my backyard.So what happens is when D1 and D3 are switched on motor runs in forward direction and when D2 and D0 is switched on motor reverses its direction.
TIP
If you look at the RC kit you will find 4 controls forward ,reverse,left and right.So the easiest way to drive the robot is use the forward and reverse channel to control one and left and right to control another.Of course can make better controls by decoding the output but this is the easy way.
LOOKS CRAPPY BUT DAMN EASY!!!!


click on the image to see clearly .
RELAY BASIC IDEA
This is the circuit to drive the motors using relays.A relay has 5 pins 2 for the energising coil and 3 for contacts .There is one movable contact and two fixed contacts .And the movable contact is in contact with a default pin when the relay is not switched on .For more tutorials on how relay works> click here .
HOW THE ABOVE CIRCUIT WORKS
So here when when one transistor is switched on the movable contact moves and comes in contact with the +ve supply and since the other end is grounded the motor runs in one direction .And the viceversa happens when the direction is reversed .(Those protection diode is not needed this transistor can withstand much abuse)
AND AT LAST PS
PS:THIS CIRCUIT MAY LOOK COMPLICATED BUT ITS VERY EASY I'VE USED THIS CIRCUIT A LOT OF TIMES .YOU CAN USE 12 V OR 6 V SUPPLY.AND YOU CAN EVEN USE A 6 V RELAY IN CASE YOU ARE USING 12 V SUPPLY(its so versatile), AND NOTHING HAPPENS WHEN 6 V RELAY IS CONNECTED TO 12 V SUPPLY (thanks to back emf)...