Tracked Robot Fabrication tutorials

The following parts were fabricated for the constructions of the robot .They are explained one by one below.

WHEELS

The wheels used in the construction of robot were machine moulded plastic wheels with hollow space inside. The diameter of the wheel is 61 mm and the width of the wheel is 20 mm.

BELTS

The belts that we have used are reinforced rubber belts .Some of the remarkable characteristics are wearing resistant, high strength, waterproof, heat resistance, crack resistance, aging resistance and longer use life.  

The ball bearings that support the rear wheels need to be housed in a housing that could support the ball bearings and it also provides adjustable facility so that the slack that occurs in the belt over a period of time can be adjusted .It also facilitates the easy removal of the belt are loosening it.

REAR WHEEL SHAFT

The shaft shown  freely inside the ball bearing providing smooth motion .One end is threaded to connect the encoder wheel and the other end is connected to the wheel. 

BALL BEARING HOUSING 

The ball bearings that support the rear wheels need to be housed in a housing that could support the ball bearings and it also provides adjustable facility so that the slack that occurs in the belt over a period of time can be adjusted .It also facilitates the easy removal of the belt are loosening it.

PROVISION FOR SLACK adjustment

As the rubber belt slacks due to temperature variation and ageing a slot was milled in the robot’s body for slack adjustment which ensures that the belt stays taut at all times.

Final Year Project Robot design

Final Year Tracked Robot Sketch Up Drawing 

Google sketch up is a very useful tool for drawing fine and detailed drawings of your robots .Its easy to use as well Below is the 3d view of my final year project .

Isometric View

Side View

The real picture of my robot ..

The body frame was made of aluminium sheet and the wheels are plastic and the belts are rubber belts .I've written about the construction in the following posts .

How to couple a robot's wheel with motor ?

COUPLING MOTORS AND WHEELS

When you have motors and wheels the question arises how do I couple them ?.As far as I've experienced they never fit together .So you have to make a coupler to couple both so that it can be removed and used later in any other robot and for easy dismantling .I've written the steps for fabricating it elaborately .You can use either ms(Mild steel ) or Brass for fabricating it .

STEPS OF FABRICATION

• First measure the diameter of the motor shaft.
• Then measure the internal diameter of the axis the wheel.
• If both match then you can fix it directly.
• Otherwise choose a rod that is at least 4 mm greater in diameter than the motor shaft.(so that you can use a miimum size of 2mm screw to secure it)
• Step turn one side of the rod slightly larger than the internal diameter of the axis of wheel to give a tight fit.
• Then on the other side drill a hole with a drill bit that is little larger than diameter of the motor shaft in the rod along its axis .This side is given a loose fit since motor can be reused .(Note this is a drill to insert the motor)
• Drill until a depth that is little shorter than the height of the motor shaft.
• Then grind the motor shaft with grinding machine to make a flat surface along the axis if your motors shaft is cylindrical. Some motors shaft will be like half cylindrical .This step is not needed if the motor is of this type.
• Then drill a hole perpendicular to the axis of the coupling shaft matching the place where you ground the motors shaft, then tap the hole to form thread and use a bolt to tightly secure the coupling shaft with motor.
• Before doing the above step don’t forget to fix the wheel.

Wheels fitted to the motors with the coupler .

MOTORS AND SPEED CALCULATION

MOTORS AND SPEED CALCULATION

When you start designing wheeled robots start from the motors .
Decide the type of motor you are going to use .

According to gear arrangement DC motors can be broadly classified into

1. Motors with Internal gear's
2. Notors with External gear's

For beginners I would recommend using motors with internal gear box motor ,since they are easy to use(they eliminate the whole process of designing and fabricating the gear box ) .Internal gear box are available from a range of anywhere between 5 to 5000 RPM .And their speed can be varied either by

1.Varying the supply voltage or
2.Pulse width modulation (PWM )

After you choose the motor you can calculate the speed of the robot to get a rough idea about how fast your robot will go .(Never forget to do this while designing a robot ,otherwise you will end with a robot that is either too slow or too fast) .
The speed calculation doesn't involve big mathematical formulas .
Measure the diameter of the wheel (in meters) that you are going to use .Then multiply it with PI(pi = 3.14159265) .This gives you the circumference of the wheel .So you get a rough idea about how far the robot moves on one rotation of the wheel .

Circumference = Diameter X PI

Most cheap motors availabe never work to the specifics .The best way to find the RPM is trial and error .Apply the required voltage(remember to connect the wheel before applying the voltage) and start a stop watch for (say) 10 seconds and see how many time it rotates and then multiply it with 6 .This gives u the approx speed of your motor in RPM .And also mark a position on the wheel to make it easier to track it visually .
After getting the RPM of your motor multiply it with the circumference of your wheel .This gives u the approx speed of your robot in meters per minute.

Speed of your robot = RPM of motor x Circumference of your wheel (meters/min)

Robocon Pick N Place Robot !

This is the video of the pick and place robot that me and my team mate madan made for
ROBOCON 2007 .I am the one controlling it and madan is the one shouting from behind :P .

Watch this video in the testing phase



This is our robot in action in ROBOCON .It looks drunken and slow because we forgot to recharge the battery ...shit we lost the match ......




WORKING
Here is the picture of the pick and place mechanism that I came up with .
The working is pretty straight forward. It has a moving and a fixed arm .
I use the nut bolt arrangement to close and open the arm .And it has a center spring
which provides the force to automatically open the arm .And I used a motor fixed
with a pipe in the shaft to rotate the nut .
Heres the diagram of it .

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)...