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.

The power of Composites

Can a sheet of aluminium withstand an impact of a 2kg bird at 700 kmph? No! It can't. Can the same impact be withstood by a sheet of fibre glass? I'm not sure or may be not. But a sheet of Aluminium reinforced with glass fibres? Yeah, it can. And thats the material used for making the body of the Airbus A380.

Lets see how it works. There are two essential properties that most engineering materials are expected to possess. One is that it should not deform considerably and the other is that the material should not fail or fracture. Now, for the body of the aircraft, a strong material that isn't heavy is required. Naturally we go for aluminium based alloys for this purpose. But is that strong enough to survive a a bird's impact at a relative velocity of about 700 kmph? Obviously not! So, there is need for reinforcement of the alloy with some stronger material. Surprisingly, the engineers have chosen glass! Glass is a highly brittle material and the possible failure of this material is through a brittle fracture. The mechanism of brittle fracture is given by Griffith's theory.

According to this theory, there are microscopic flaws(cracks) which propagate to form bigger cracks on the application of excessive stress. A part of the energy from the load is used to create the new surfaces as the new cracks are formed. When these cracks propagate to the surface, fracture occurs and the material fails. This is the mechanism by which glass fractures. When glass is heated and drawn into a fibre, these microscopic cracks are eliminated. Thus, when glass is in the form of fibres, fracture is prevented to a greater extent. These glass fibres are used to reinforce the Aluminum alloys and this composite is used to build the body of the A380.

A typical fiberglass sheet.

I feel the need for some research!

Well, its been a habit of mine to write exactly what I understood. In my previous posts, I've just given some (vague) ideas of how certain things work and nothing more. Blogging for more than a couple of years now, I feel that its time for me to take my writing to the next level. Yeah, from now my posts would have not just simple understandings of various phenomena or gadgets, but also some theory supporting it!

And yeah, as I promised, my next post will be about the composite used in the construction of the Airbus A380.