Domino effect - Its more than just a fall

There is none who hasn't heard of the domino effect. Its the chain reaction triggered by one falling object on the other (dominoes) which in turn fall on the other and so on. Simple isn't it? But when I was surfing the net reading about the energy conversions involved in a domino effect, I was amazed to see how naive I have been in thinking that the effect is nothing but a successive fall of dominoes. Here are some of the interesting aspects of a domino effect that I came across

1) The speed

The speed of the domino effect depends on the distance between the successive dominoes. The farther they are placed apart, the slower is the progression because it takes a longer time for the falling domino to knock down the next one - common sense. 

2) An Infinite arrangement of dominoes

An infinite dominoes set poses some interesting questions. Will the system continuously lose energy continuously through heat and sound and eventually come to a halt? The answer is no. The energy of the system comes from the potential energy of each of the dominoes that was stored while setting them up in a metastable position. An initial trigger to the first domino will convert its potential energy into kinetic energy while falling and a fraction of this kinetic energy will push the next domino to an unstable position thereby making it fall and converting its potential energy into kinetic. Thus the system is self sustained and never comes to a stop. In fact, as the first domino pushes the next at a speed, the second one falls faster than the first. This in turn topples the next one even faster and thus the progression is actually accelerated.

So, if the progression is accelerated, will an infinite dominoes system reach the velocity of light at one point? the answer is no again. Consider this analogy - a ball falling towards the earth's surface from about a height of 1000 km should ideally reach a velocity of 42 km/sec when it reaches the surface. But that does not happen because the atmospheric air dampens its acceleration and makes it reach a "terminal velocity" which will be constant till it touches the ground. Here energy is lost by friction and buoyancy and an equilibrium is reached. In a similar way, in a domino-effect, the energy is lost during the impact through heat and sound. this energy loss is more when the speed of impact is more. Thus the system reaches a point in time when the acceleration and energy loss reach an equilibrium and the progression will be at a constant velocity from then on.

There may be still more to a domino-effect when you consider the size and geometry of the dominoes. May be I'll look for more on this topic and write about it sometime later. From now, when you witness a domino effect, remember, there is more to it than what meets the eye! ;)

References: Wikipedia, www.physicsforums.com

Get a head start on simple robotics

I'm back to posting something almost after a month. Still I'm lazy enough to post the same thing which i've wriiten for CSAU's(Computer Society of Anna University) next edition of cursor magazine. Its about simple robotics and here it goes... 


check out this moving butterfly robot

‘Robotics’ is a very common word among the guys and girls of CEG. Many people misinterpret this term as something big and hi-fi. Yeah, even for me the first thing that comes to my mind when I hear the word ‘robot’ is ASIMO! In reality, the bots we actually make at college level are quite simple and fascinating. In fact, making robots will make a great hobby. I was fortunate enough to have seniors who helped me a lot in gaining some insight into this field. In this article, I’ll discuss some theoretical aspects for building a manual radio-controlled bot.

Invariably, all the bots that we make at college move on wheels (on belts or chains too) and DC motors drive them. As Wikipedia defines a robot as an Electro-Mechanical entity, we have to primarily design a robot on Electronic and Mechanical point of view.

The mechanical design includes the chassis design, drive system and the mechanism to complete its objective. The chassis design is simple. You just have to decide where to place the motors (2 or 4 according to the bot’s objective), battery and the circuit boards. Make sure that the centre of gravity of the robot is as low as possible for greater stability. For the drive system, there are two major types

· Steering drive

· Differential drive

The steering drive is the drive system used in cars. A rack and pinion arrangement is used to steer the front wheels. This type of drive can be used in building bots for which speed is of great importance as the bot can be driven forward as well as be steered to any one direction simultaneously. But the great disadvantage is that building a precise steering mechanism is highly complicated. So, we practically don’t use this system for most projects.

Differential drive is used in almost all simple robots. In this system, a left or right turn is achieved by the differential motion of the left and right wheels. The turns can be achieved in more than one way.

Left turn – 1) Right wheels rotating in forward direction while the left ones aren’t moving (Arc turn)

2) Right wheels rotating in forward direction and the left wheels in the reverse (Spot turn)

3) Right wheels rotating faster than the left wheels. (This type is not in practice)

The right turn can be achieved in a similar way. The great advantage of this system is that it is very easy to build the electronic control. However, the bot has to stop moving forward every time it needs to turn.

There is another type of drive – the pivoted drive. This method is used for making precise turns. This is fit for use only in autonomous robots and hence I am not discussing that now.

Additional mechanisms are based on the bot’s mission. It may be a hand to pick objects, a wedge in front for sumo bots or event rack and pinion arrangements to lift objects. These things can be designed according to your choices. Often simple ingenious designs work better than complex mechanisms as greater the complexity, greater the chances for failure.

Electrical design

For a radio controlled bot, we require a transmitter and receiver module. We need not design these components. The transmitter and receiver module can be hacked from a RC toy car. I’ve given a layout of the electrical design below

The Receiver module operates at 5V whereas the motors we usually use are rated at 12V. So, in simple words, the motor driver converts the 5V output signals from the receiver to 12V and gives them to the various motors used. This driver circuit is the only circuit that we make originally for a simple bot. A typical transmitter-receiver module handles 4 signals. I’ll write on how to hack a receiver module from a toy car and how to use those four signals to effectively operate the bot in the next post.

Landing Gear of the Airbus A380

Before writing this article, I just want to say - "I'M BACK!"

I switched to the National Geographic channel at 10.30 AM and found that the program was to end at 11 AM. The program was about the making of the world's largest airliner- The Airbus A380. At that time of the program, the material used for making its body was being shown. It was actually a composite - Glass and Aluminium together. I'll post a separate article about this. For now I just want to write about what impressed me the most - the landing gear!

The landing gear is one of the most important components of an aircraft. For an aircraft like the A380, it should be strong enough to bear the immense weight ( The Airbus A380 weighs about 276.8 tonnes when empty) as well as absorb the shock off landing. For such a massive component, the people at Airbus came up with a very simple yet effective design for the shock absorber. Its the 'cycle pump' concept. The concept is simple- the shock absorber is a piston that moves inside a cylinder just similar to a cycle pump. As the air inside the cylinder is compressed, the shock is absorbed. In the A380's landing gear, instead of just air, oil is used As greater energy is required to compress the highly viscous oil into a chamber, greater shock is absorbed and the landing is smoother. In the NGC program, the engineer who designed the shock absorber demonstrated its capabilities using ordinary cycle pumps filled with water. It was amazing to see how those pumps absorbed the shock when a big piano was dropped(the array of pumps were fitted under the piano) and kept it intact!

And they even showed a footage of a Korean Airlines' Boeing plane landing safely in a crosswind with ONLY ONE wheel touching down first. That very well described how strong they ought to be! Hail engineering! :-)

SAE Baja 2010

As soon as I saw a poster in my class's notice board inviting second year students for an open interview for recruiting second year members for CEG's SAE(Society of Automotive Engineers) Baja 2010 team, I remembered the baja vehicle that was displayed during Kurukshetra '08. Building an ATV(All Terrain Vehicle) during the second year of your Engineering course sounds great! I badly wanted to be a part of that team. I attended the interview with a strong resume backing me. After the 15-minute interview(quite long for this kind), I came out confident of getting selected. As I expected, my name was present in the selection list.

Now that the team is finalised and registered for Baja 2010, its time to wonder about what exactly we're gonna do - build an ATV from scratch? Probably yes! Baja tests every aspect of your vehicle - the design, stability, power, speed and aesthetics too! The venue for baja 2010 is the same as that of 2009 - Pithampur, Madhya Pradesh. As we'd be starting our work soon, I guess there are exciting times ahead!

This is the SAE baja's website... http://bajasaeindia.org/

The K! Project

Well, I'm back to take care of my log after quite a long period! Yeah, its not easy even to have proper meals when you are a part of the Project team of K '09. So, now that I'm back, without much bla bla bla, I'll directly jump into what I wanted to do all these days - post about our Kurukshetra Mega project.

This year's Mega project for Kurukshetra was A Strategic All-Terrain Robotic Platform. I was a part of the Mechanical Team comprising two - myself and Arun seashatri for the project. Santhosh, Vijayakumar and Karthikeyan took care of the electronics and programming part.

The objective
Our objective was to build a small robust unit that could navigate in rugged terrain and tackle small obstacles and most importantly do a surveillance work.

The Construction
We had certain things to keep in mind before starting the construction..

1) The most important thing - ALL TERRAIN NAVIGATION
2) Effective suspension - For enhanced camera feed from the vehicle
3) Sturdiness - our imported 130 RPM, 24 V motors may very well disintegrate the unit if it has a weak frame. Moreover it should hold 2 12 V UPS batteries each weighing more than 2.5 Kg.
4) An effective arm to pick small objects

Now, for the first concern - all terrain navigation - we had to decide on the type of wheels. We had a look at the trainer wheels in kids' cycles and thought that it would work out for us. Then we worked on the suspension. We fell upon the springs used in the gear box of ambassador cars. With the essential parts in hand, the design of the body was done easily. All that we had to do then was - go to the workshop; cut the metal (we used Mild Steel) ; put the things in place and bolt them! Wait, I forgot to tell about the arm! Even before deciding on the wheels, we finished the construction of the arm using 6mm thick Aluminium plates. Seshatri came up with an effective idea of a pulley system that could make the maximum use of low torque motors. It was very simple yet effective considering the limited options we had.

Finally after some two months(semester exams slowed us down), we were done with the chassis. It was time for a test run! The first test run gave us a BIG BIG BLOW!! Yeah, we totally forgot the "Buckling and twisting" nature of springs during the construction. The very high torque motors that we used made the springs twisted in different directions and caused big variations in the alignment of wheels. We had to use unconventional methods like placing bolts and clamps at appropriate places to control the twisting. But we couldn't stop the buckling. Only during the next test run, we realised that buckling - which is considered to be a bad aspect in suspension, actually helped us save the bot from the juggernaut of the motor!! The initial acceleration was immense that it could have toppled the bot without the spring that absorbed the force. Finally we added the gripper to the arm and mounted the arm. Santhosh turned up with better wheels for the bot - those wheels used in trolleys seen at airports. That type of wheel impressed all and we used that finally. (I'm simply sayin "we mounted the arm".. this is an understatement! we had to work for days and experienced sleepless night in doing these works!)

The Base Console
Atlast, after a lot of fine tuning and adjustments, the base console was ready. The base console was the most attractive part of the bot. The base being a computer, the console application displays
1) The camera feed
2) Parameters like system voltage, system current, motor supply voltage, remaining battery power etc..
3) The GPS module placed in the bot displays the coordinates of its current position and its velocity
4) Google map embedded in the application provides visuals of its location

Due to unexpected and shocking happenings like burning of TV tuner card in the computer, failure of the wireless transmitter of camera and so on just on the day before the date of display, we had to postpone the date of display by 2 days. After doing the necessary changes, we finally had a good show during the display. One thing which most people like about it was the unique suspension system ;-)..

Right now, I dont have the screenshots of the base console with me. So, I'll upload them later. as for now, I'll upload the only pic of the bot that I've got

Science in Sports - The Magnus Effect

My brother looks back at the cylindrical filter of a reverse osmosis unit substituted for a lone stump, toppled by the plastic ball I threw. He had played a perfect forward defense that would have made Rahul Dravid proud! Yet the ball, tracing a curved path in the shape of a banana had whizzed past the outside edge to hit the "stump". "Yeah, that's the Magnus Effect", I thought to myself. The same effect that helps Roberto Carlos score a goal as well as threaten the ball boy standing 10 yards away from the goal!

So, what is the Magnus Effect? When a cylindrical body or a spherical spins and moves in one direction through a fluid, experiences a force perpendicular to the direction of its velocity.



Consider there is no wind and the velocity of the ball is V. So, the relative velocity of air around the ball with respect to the ball is V. Now, due to the spin on the ball, the air in contact with its surface acquires some velocity. In the above picture (I got the picture from wikipedia) you can see that the flow of air is assisted by the spin. Therefore the relative velocity of air will be greater than V. On the other side, the flow is being opposed by the spin and hence lesser relative velocity of air with respect to the linear motion of the ball. This difference in velocity, in accordance with Bernoulli's theorem, will create a difference in pressure between the top and bottom side. With the bottom side having a lesser pressure due to high velocity of air, the ball experiences a net downward force.

This force is given by the relation,
Here F is the force, ρ is the density of air, V is the relative velocity of air over the ball with respect to the ball, A is the area of cross section of the ball and l is spin ratio.

l = rw/(2*linear velocity) where w is the angular velocity of the ball and r is its radius.

Now that you know what exactly is the magnus effect, lets see its influence in various sports. And yeah, in the order of my favourite ones! ;-)

Cricket
I guess most people know that the lateral movement of the cricket ball when a fast bowler bowls is due to the varied degree of smoothness on the two sides. So, this has got nothing to do with the magnus effect though bernoulli's theorem comes into play. In cricket the only scenario where I've observed this effect is when a spin bowler bowls.

When an off spinner bowls, he gets the ball to drift away from the batsman and when a leggie bowls, the ball drifts into the batsman. When the ball leaves the bowler's hand(in both cases), it spins around an axis that is slightly inclined to the horizontal. So, the angular velocity has a component in the horizontal plane and this accounts for the drift!(Hope you could visualise what I mean)

Tennis
In tennis the magnus effect is the reason behind the dip in the ball's trajectory after being hit. In tennis terminology this is called "topspin". When Roger Federer imparts heavy topspin on the ball with a forehand shot, the initial path traversed by it would apparently take it way outside the baseline, but the considerable force acting in the downward direction keeps it in play!

A similar action is observed in Table Tennis too. Without the help of the magnus effect there is no way to keep the ball within the limits of the table!

Football
Beckham does it, Gerrard does it, Roberto Carlos does it and almost every one of those skilled players does it!

Check this video http://www.youtube.com/watch?v=-wL5w_GxIoo
Its self explanatory!!!

But wait! A cricket ball is imparted with much more spin that that on a football and yet the football moves more! The reason is simple.

• *Magnus force is proportional to the area of cross section of the ball. A football is larger than a cricket ball.
• *F=m*a, when mass is less the acceleration is more for a constant force. Football is lighter than a cricket ball(i guess so :P)

The other sports like golf and volleyball are also influenced by Magnus effect.

Learnt some facts from wikipedia.

Water rockets!

Well, I was wondering how could water under pressurised condition(yeah, i know liquids are incompressible) ever propel a rocket! That was when i first saw the problem statement of the ROCKETRY event of Kurukshetra '08 and decided this is not for me! Now when I look into this field, I'm really amazed by the amount of physics involved with water rockets(or bottle rockets)!

Now that i'm so impressed by the working of water rockets, i'm determined to post a small article on it!

WHAT YOU NEED?

• A 2-litre used coke [or whatever] bottle
• A hacksaw
• A compressor(To pump air)
• Any ligth weight material to make the nose and fins(The same plastic from which the bottle is made would do well)

Now, I dont wat to give step by step instructions to construct the rocket. Instead I'll scatter few pictures. Being a "Techy" person you could grasp the details from these pics. ;-)





The nose and fin setup is just enough for you to get an insight into the construction. And yeah, about the nozzle setup, as I've not yet built a water rocket myself, I'm not sure about that part. Depending on the type of compressor or pump you use, you can have your nozzle set up in the corresponding style.

Now, lets get into my favourite part - how it works! ;-)
I always like KISS - Keep It Short and Simple :P. So, let me keep it short. The major parameters on which the working of the rocket depends are (i) Pressure inside the chamber, (ii) Diameter of the nozzle, (iii) Quantity of water inside the bottle. And yeah, the flight of the rocket also depends on the weight of the bottle used and the alignment of fins.

The Pressure:
The pressure determines the stored energy inside the bottle which in turn determines the thrust developed. As water is incompressible, energy is not transferred to it. It is stored only in the compressed air. The launch pressure may vary with the size and the type of bottle used. It may be between 500 kPa to 1000 kPa.

The Nozzle:
The nozzle may be the standard soft-drink bottle's one with an approximate diameter of 22mm. Or it may be of a reduced size - 9mm diameter approx. The size of the nozzle affects the thrust produced by the rocket. Larger diameter nozzles provide faster acceleration with a shorter thrust phase, while smaller nozzles provide lower acceleration with a longer thrust phase.
Quantity of Water:
The quantity of water is a very important parameter. It determines the duration of the thrust phase. Mathematically, the ratio of the volumes water and air in the bottle for maximum efficiency is 1:2. For an efficient flight, the thrust should be in three phases. In the first phase, the exhaust is completely water. This flow must be laminar for maximum thrust. In the second phase, the amount of water would have been reduced. So the exhaust consist of both air and water and the flow will be turbulent. This will be seen as a spray of water particles from the nozzle. The last thrust phase consists of exhaust of air.


The above picture shows the laminar and turbulent flow phases clearly.

Well, this is all I've read about water rockets till now. There are still a lot of technicalities associated with water rockets. And now its your turn to build and launch your own rocket. Happy Launchin'! :-)