Build A Robot

Abstract:

Robot is an automatically guided machine which is able to do tasks on its own, almost always due to electronically-programmed instructions. Robotics is the engineering science and technology of robots, and their design, manufacture, application, and structural disposition. It is related to electronics, mechanics, and software.

Main Article:

Introduction

I read an article some where on the internet is about how to build a robot. Here I am just sharing with you. The word robot was introduced to the public by Czech writer Karel Capek in his play R.U.R. (Rossum's Universal Robots), published in 1920. The term "robotics" was coined by Isaac Asimov in his 1941 science fiction short-story "Liar!"

Robot is an automatically guided machine which is able to do tasks on its own, almost always due to electronically-programmed instructions. Robotics is the engineering science and technology of robots, and their design, manufacture, application, and structural disposition. It is related to electronics, mechanics, and software.

How to build a robot?

            Before you continue you should have knowledge of electronics, mechanics, controls, programming, and even as broad as understanding animal behavior and human psychology.

            While making your very first robot your goals should be to just learn all the basics:

  • how to program
  • how to use the tools, terminology
  • learn basic technology
  • how to get robot parts(Batteries, wheels, motors, sensors)

What do you need to start?

First you need a design. That is how your robot looks like is? Browse the web for robot galleries. Remember, only bother looking at the really simple robots, DO NOT get imaginative or creative on your first robot. What you want is a dumb little 2 wheeled thing that just doesn't commit suicide by driving off your table. And for a beginner, that can be extremely hard for doing himself.

Most basic algorithm for a robot is differential drive. It is a method of controlling a robot with only two motorized wheels. What makes this algorithm important for a robot builder is that it is also the simplest control method for a robot.

The term 'differential' means that robot turning speed is determined by the speed difference between both wheels, each on either side of your robot. For example: keep the left wheel moves reverse and the right wheel moves forward, then the robot will turn left. If you are clever with it, or use PID control, you can get interesting curved paths just by varying the speeds of both wheels over time. Don’t want to turn? As long as both wheels go at the same speed, the robot does not turn - only going forward or reverse.

The differential drive algorithm is useful for light chasing robots. This locomotion is the most basic of all types, and is highly recommended for beginners. Note that this algorithm doesn’t just work for wheeled robots, but also you can use the same algorithm for tank tread type robots and biped robots.

How to Use This Algorithm

Place two motorized wheels on your robot, one on either side. Send your move commands to the motors by either using a motor driver or H-bridge. Or if you are using servos, just send the required pulse width. Note that this algorithm works great with the photovore algorithm.

Pseudo code:

input sensor reading

make decision based on sensor reading

do one of below actions:

to drive straight both wheels move forward at same speed

to drive reverse both wheels move back at same speed

to turn left the left wheel moves in reverse and the right wheel moves forward

to turn right the right wheel moves in reverse and the left wheel moves forward

You can also get interesting curved paths just by varying speeds of both wheels. But for now, let’s just keep the algorithm binary to make your first program easy. Don't forget a castor (low friction that drags). Remember from geometry you need 3 points to make a plane. Now you have a whole list of design issues.

Requirements:

Wheels: Big wheels will let your robot move faster. Small wheels for slower. You can take 2 wheels with 2-3" diameter for your first robot.

Motors: 2 motors that sounds simple. Voltage: 5V-8V. Torque: double what you think you will need.

For an optimal robot choosing motors would involve calculations of weight, gearing ratios, desired terrain, desired velocity and acceleration, voltage, power consumption, controllability and a whole range of things too overwhelming for a beginner. You keep your robot as light as possible. But remember, bigger the motors, shorter your battery life, and more expensive and complicated your motor control circuitry will get.

There are many websites selling DC motors, servos. Both are equally as complicated to implement and cost about the same. Each has their own advantages. Servos are much easier to control, but they generally are less energy efficient, have explicit voltage requirements, and are less intuitive.

Batteries: When buying a battery make sure they are rechargeable, have high mAh (energy capacity), and can output at least an amp at any time. Consider putting batteries in both parallel and in series to vary/control total voltage and mAh.

To make a small sized robot and buy two NiMH 6V battery. Get two so you can isolate motor power from circuitry power. One battery for motor and one for circuits. A NiMH will be fine for circuits, and either NiCad or NiMH for motors, depending on expected power requirements from your motors. Choice is yours.

There are many types of batteries, so let’s just talk about the 3 most common.

Alkaline batteries are the most common, easiest to get, and cheapest too. However they are useless, don't buy them. They have low power capacities, are heavy, have trouble supplying large amounts of current in short time periods, and get expensive to constantly replace.

NiMH (Nickel Metal Hydride): You can recharge them as much as you want; they have good current output, and have the highest energy capacity. However they are more expensive than the Alkaline & NiCad (Nickel Cadmium). NiMH batteries usually take like 5-10 hours to fully recharge depending on various factors.

NiCad: (Nickel Cadmium) batteries are good for small to medium size range robots. They have the highest current output, are more affordable than NiMH's, and can be recharged within one or two hours. Older cell phone batteries were often NiCad. However, recharging NiCad batteries is a black art. Ever notice how some older cell phone batteries just do not last as long on a single charge as when you first bought it? This is called memory effect. A NiCad, over many charges, can only store less and less energy after each recharge. To prevent memory effect, whenever you wish to recharge your NiCad, you must first fully discharge it. And remember, NiCad batteries contain toxic cadmium stuff, so save a squirrel and recycle/dispose of it properly.

Micro controllers: A ready made circuit thing is easiest. The most popular being PIC, Atmel/AVR, ARM, and BASIC Stamp based. Stamps are easier but offer less functionality. If you know programming basics, better you go with AVR based.

Just literally plug in your battery, your motors/servos, and your sensor input/outputs, program it. Your circuit thingy is finished!

Sensor: A battlebot is not really a robot in that it has no sensors and can't make its own decisions, you want it autonomous right? You can however skip this section and use a RC remote attached to your controller if you want a battlebot.

Photo resistors: get 2 photo resistors, put one on each side of your robot, and run a binary algorithm. If the sensor on the left see lighter than the one on the right, tell your differential drive to turn left. If they see the same amount of light, tell your robot to drive straight. Aim the photo resistors on the ground and you have instant obstacle avoidance - your robot will avoid the shadows cast on the ground by objects in the way.

Basically all you need to decide is shape, location of all parts, and how to connect the parts together. The more you plan it out, the cheaper the robot and the less time you will need to build it. Remember to plan where the screws go, how you will cut your parts out of sheets of aluminum, HDPE, or cereal boxes, and to balance the weight. Scrap heaps, old toys. You can use Velcro and double sided sticky tape often as it allows you to make modifications easily. Batteries should ALWAYS be attached with Velcro - makes recharging easy. Expect to modify a lot on your first robot, so design your robot to be easily modified.


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Author:  sheela
Posted On:  Saturday, 13 October, 2012 - 12:57

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