Build Your Own Combat Robot phần 2 pot

S we said in Chapter 1, it’s good to let your imagination run wild

when you begin making plans to build a bot. However, while you can dream up all

kinds of crazy ideas for a robotic creation, keep in mind that you may not have the

time—or even the technology—to build most of them. We can’t begin to tell you

how to design the “perfect bot,” any more than we can convince you of what the

perfect car or television set is. Everybody has their own idea of what’s best. Yes,

we authors have our biases and feel comfortable with certain techniques and de￾signs that have been tested over a number of years, but a prospective bot builder

can easily arrive at a better idea than anything we’ve come up with in the past.

Read this book and others, talk with respected people and experienced combat

warriors, sketch out your ideas, and then just go for it.

Start your design process by deciding on exactly what you want your bot to do.

If you’re planning to build a machine for BattleBots, you’re going to have to take

an approach quite different from the one used for making small autonomous ma￾chines designed to run a maze or blow out a candle in the popular Trinity College

Robot Firefighting Contest. A bot designed to act as a servant in your home may

be every bit as heavy and complex as a warrior bot, but it doesn’t need to be able to

survive the blows of a weapon of another machine or travel nearly as fast.

Experience has shown that electronics and computing power are not the limit￾ing factors in bot construction; it’s the mechanics, sensors, and related software

development that choke a project to a stop. “How do I physically build the thing?

What type of sensors can I use? How do I write the code and what language should

I use?” are the questions that flood experienced builders’ minds.

Of course, if you’re building a BattleBots-style (radio control) machine, you

probably won’t need any software, and the “sensors” are your own eyes as you guide

it across the floor of the battle arena. Physical and mechanical design are most crit￾ical in these large bots. They require more sophisticated machining techniques

than most bots because they must endure an environment that is far more hostile than

the average home.

22

The Robot Design Approach

The first step in designing a new bot is deciding which contest the bot will be built

for and getting a copy of that contest’s current rules and regulations. The rules

outline the weight and size limits for each weight class, as mentioned in Chapter 1,

and list weapon types that are allowed and not allowed. They also list safety re￾quirements, electrical requirements and restrictions, and radio control restrictions.

Read and understand the rules thoroughly. This will set the initial physical con￾straints in your bot’s design.

If you’re designing a robot for multiple contests, you should obtain sets of rules for

all of them and make a list of all the common rules and non-common rules. When

you have this information put together, you’ll be able to create a list of the most re￾strictive rules for each of the contests, which will help you guide your overall bot

design. Building a bot to the most restrictive rules will allow your machine to be

entered into each contest without significant modifications.

Chapter 2: Getting Started 23

Like I said in

Chapter 1, I got

started in robot

combat for the fun. When I came

on board, there was no TV coverage

or anything fancy. Tickets were

sold locally, and it was promoted

through grass-roots efforts. A

friend and I happened to learn

about it via the Internet and were

two of only a handful of people

who came to the competition from

outside California.

Back in those early days,

getting people involved was a

challenge because everything was

so new and no one was really sure

how to promote the idea. Now, of

course, there are lots of popular

organizations where robot builders

can compete, such as

BattleBots, Robotica,

or Robot Wars.

The sport has changed a lot in

five years. Because robot combat

has gotten more commercial, the

standards by which entries are

judged have gotten far more

stringent. When I first competed,

the rule book was maybe five to

seven pages of safety tips. Now,

the rule book for competing in any

of the major contests is 60 pages

of dos and don’ts, plus another

50 pages of technical specifications

that competing bots must adhere

to. It isn’t just a game anymore. It

has become serious business for the

people involved, and the promoters

expect those who enter to bring a

robot that is both safe and exciting

to see in action.

If you’re going to build a bot, let

it be your love of the sport—not a

desire for glory or fame—that

brings you into the arena. People

thinking of getting into this with

visions of becoming “The Rock” of

BattleBots had better check their

servos at the door. Chances are

your first entry will die a quick,

smoldering death, so keep your

ego in line. As long as you’re there

for the joy of the game, you will

have as much fun bashing,

smashing, and chopping your

opponents into miniscule metallic

bits as I did!

—Ronni Katz

First

Person

24 Build Your Own Combat Robot

Even if you’re just building a bot for fun, we recommend getting a copy of one

of the main contest’s rules. A good example of rules and regulations can be found on

the BattleBots Web site (www.battlebots.com). Their safety guidelines and re￾strictions should be followed in all bot building. Most of the rules are there for the

safety of builders and spectators alike.

Once you have the physical constraints written down, you can start laying out

the conceptual design of your bot. Sketch out what you would like your bot to

look like and do. Include the unique features and weapons you would like your

bot to have. A lot of this is paper-and-pencil or CAD (computer aided design)

work. Next, make a list of performance goals you’d like to achieve, such as how

fast you want your bot to go or how much weight you want it to be able to push.

How much must the armor withstand in punishment, and how will your bot’s

weapon attack the enemy? This is all top-level generic design information; you

don’t need to get into nitty-gritty details like miles per hour or pounds of pushing

force yet. That comes later.

The second list includes what you are aiming for—the ultimate goal. Some peo￾ple call this the brainstorming part of the design process. The ideas come out here.

As is the case with any brainstorming session, there is no such thing as a bad idea.

Let the ideas flow, and come up with some cool bot concepts. It is usually good to

come up with a handful of them.

After this, the conceptual ideas must be trimmed down to meet the physical

constraints of the contest. Yes, this means you’re going to have to toss out your

idea for a laser-guided rocket launcher. (It’s a great idea, but it’s not allowed in

any combat robot event.)

In all competition robots, the following subsystems are part of each bot. Each

of these subsystems relates to the others and affects the overall design of the bot:

■ Robot frame

■ Drive motors

■ Power transmission

■ Batteries

■ Wheels

■ Electronics

■ Radio control system

■ Weapons

■ Armor

Probably the first consideration in your robot’s design is how you’re going to

make it move. Your choices are many, and could include slithering, swimming,

floating in the air, or even climbing up a wall or rope. More than likely, though,

you’re going to want a mobile bot that travels across a floor, and this will mean

legs, “tank” treads and tracks, or wheels.

Wheels are the most effective way of providing propulsion to a bot. They are

cheap, and easy to mount, control, and steer, and there are several methods you

can use. We’ll discuss all this in Chapter 3. There are many sources of bot wheels,

from toys for the smaller bots to small trailer tires for larger machines. Some

builders have used wheels from industrial casters, lawnmowers, go-karts, and

even small bicycles. Your choice depends on the size and steering configuration of

your bot’s design.

The majority of bots use differential or tank-type steering (also known as “skid

steering”). This means that the bot uses different speeds for left and right wheels (or

sets of wheels), causing the bot to go straight, or to one side or the other. Having one

wheel stopped and the other moving makes the bot pivot on the stopped wheel, and

vice versa. Having one wheel move forward and the other in reverse makes the bot

spin about its center axis. (We’ll discuss this in more detail in Chapter 3.)

Once you choose your locomotion method, the first set of major components

you need to identify are the motors. Most motors operate at speeds that are way too

fast to control the robot. So, you’ll need a gear reduction. Some motors have built-in

gearboxes, while others require a speed reduction system. This can be in the form of

gears, sprockets, belts, or even gearboxes. Chapter 6 will talk about these various

power transmission methods. The advantage of a gear reduction is an increase in

the torque to the wheels, which gives your bot more pushing power. Another reason

you should select your motors first is that they will dictate your electrical power

requirements, which affects the battery and motor speed controller selections.

Chapter 2: Getting Started 25

FIGURE 2-1

The welded frame

structure of Minion.

(courtesy of

Christian

Carlberg)