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.
L
ike I said in Chapter 1, I got started in robotcombat 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, orRobot 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 BattleBotshad 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,
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 theBattleBotsWeb 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 agreatidea, 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
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.
FIGURE 2-1
The welded frame structure ofMinion.
(courtesy of Christian Carlberg)
Chapter 4 will discuss motor performance requirements, and Chapter 7 will de-scribe various motor speed controllers.
The next step is designing the bot’s frame. This is the core structure of the bot that holds the motors, drive shafts, bearings, gearboxes, wheels, batteries, and motor controllers. The core structure should be solid and rigid, as the rest of the bot will be attached to it. Remember when you’re designing the frame to leave space for the batteries, motor controllers, and weapon actuators. Another point to keep in mind is your robot’s center of gravity. Keep it as low as possible to improve stability.
Okay, so you’ve determined your power requirements. Next, you need to know the current draw specifications from the robot motors. It is best to estimate this based on worse-case situations. The last thing you want to see happen is your bot stop in the middle of a match because it ran out of energy. Assuming that your bot is running at stall-current conditions all the time is the absolute worse-case scenario, but this estimate is unrealistic since stalling the motor for 5 minutes will destroy the mo-tor. However, assuming your robot is running at 100-percent stall current draw for 20 percent of the match time, and at 50 percent the stall current for the remain-ing amount of time in the match, should give you a good estimate on the maximum amount of current that you will need. Select your batteries based on the information contained in Chapter 5. Once the batteries are selected and the dimensions of the batteries are determined, a battery housing should be designed for the bot. The bat-tery housing holds the batteries in place and protects them inside the bot.
Knowing what the current requirements are for your bot determines the motor speed controller. You’ll find information about motor speed controllers in Chapter 7.
When you’re installing the motor speed controllers, you should have features in the design to allow for cooling. Motor controllers get very hot when near-maximum currents are running through them. You may even need multiple-speed controllers, depending on how many motors you’re using.
FIGURE 2-2
A robot using two Victor 883 motor controllers and the Innovation First Robot Controller for motion control.
(courtesy of Larry Barello)
Now, it is time to add the weapons to the design process. You need to design a support structure to support the weapons and their actuators. The support struc-ture should be mounted to the main frame, and the support strucstruc-ture needs to be very strong. As Newton’s Second Law says, “For every action, there is an equal and opposite reaction.” In other words, any force your weapon imparts onto an opponent will elicit equal reaction from the opponent onto your bot. Thus, the weapon support structure needs to be able to withstand those forces. Chapters 9 and 10 discuss construction and weapons techniques.
The last part of the mechanical design process is the armor. You should design your armor to be replaced, because it will inevitably get damaged during combat.
You don’t want to damage your own bot just trying to replace the armor, so it needs to come off fairly easily—when you want it to. Sometimes the armor and the frame are the same thing. In other words, there is no armor other than the frame itself.
Chapter 9 discusses the various materials that make good armor.
At any time during the mechanical design process, you can select which radio control system and “robot brains” you want to use. For driving a bot, you need at least two control channels—one for forward and reverse, and the other for turn-ing left and right. This is true for bots that have channel mixturn-ing. With no mixturn-ing, you would use one channel for the left wheels and one for the right wheels. Addi-tional channels are for controlling the special features.
You might want to automate some bot functions, like shooting a spike when the opponent gets within 1 foot of your bot. Here is where you specify the types of sensors for detecting the opponent and figure out how to mount them inside your bot. You’ll probably need to have a microcontroller inside the bot to process and interpret the sensor results in order to control the weapon. Before you implement
FIGURE 2-3
A robot showing how badly its
armor was damaged at
aBotBash tournament.
(courtesy of Andrew Lindsey)
any computer-assisted functions, your bot should be built and tested with all man-ual control. Once the bot works to your satisfaction, then you can add the auto-matic features.
All of the preceding design steps should be done, as much as possible, on paper or CAD before you start cutting parts to assemble the bot. This will save you from having to remake parts due to design changes. You don’t absolutely need to have CAD software to do this, but CAD does give you more professional-looking re-sults. You can use regular old-fashioned graph paper, too. Some people have even used chalk on their garage floors to design bots in full scale. Do whatever you’re most comfortable with.
t i p Expert machine designers use CAD (computer-aided design) software; so if you want professional-looking results, you should consider getting a CAD program. CAD is so widely used among roboteers, in fact, that PTC (makers of Pro/E CAD software) has sponsored the last three seasons ofBattleBots. Each team who showed up at the competition and asked for it got a free one-year license of the software, which normally retails for $21,000. Other CAD packages are available for a lot less money.
FIGURE 2-4 This robot,Slap Happy, was built using plywood as templates before metal parts were fabricated.
(courtesy of Dave Owens)
The Game of Compromise
There has probably never been a bot made that didn’t involve some level of com-promise on the part of the builder. This is where your time-, money-, perfor-mance-, and availability-related trade-offs occur. We builders rarely get the chance to use the best parts available, and therefore must settle for what we can get. This is where you need to let go of your idea for a dream bot and start looking at your project more realistically.
For example, say you want your bot to move at 20 mph and you want to use 8-inch diameter go-kart wheels. To move at this speed, the wheels need to turn at 840 rpm. Now you have to find a motor that can deliver that speed. You search all of the magazines and catalogs you can find, scour the Internet, and you still can’t find a motor that will give you the speed you want. This means you’ll need to build a gearbox that can change the motor speed to the desired 840 rpm wheel speed.
Here you will be faced with lots of options, such as spur gears, sprockets, belts, worm drives, and so on. In your search for motors, say you also found some gear motors—you pick a few motors, and then calculate what gear reductions you need to get the right wheel speed. At this point, you have several motor and gear options to choose from to get your robot to move at 20 mph. So, now you have to choose which combination you want to use.
FIGURE 2-5 AutoCad was used to design Live Wires
prior to fabricating parts.
Before blindly picking one, you should look at how this selection will affect each of the other systems at work in your robot design. For example, for a given horsepower rating on the motors, a 24-volt motor will draw about half the current as a 12-volt motor. That’s a good thing, right? Not necessarily, because running at 24-volts will require two 12-volt batteries—which increases the battery storage area and robot weight. That’s a bad thing, right? Well, again, not necessarily. A 12-volt battery might not be able to deliver the current to drive a 12-volt motor, but will have plenty of current for driving a 24-volt motor.
This is why you make the system interface drawings first. When you pick a component to use, you update the interface requirements, such as weight, voltage, current, spacing, the need to add new subcomponents or delete old components, and so on.
A bigger part of the compromising process occurs when you build your bot around existing parts. Obviously, life gets a little easier when you can build with stuff you already have, but often this means getting a bot that’s less flashy than you envisioned. For example, say you were planning to include heavy-duty motors on your bot, but the ones you had in mind are hard to obtain, and you happen to have a couple of wheelchair motors lying around the garage (bot builders tend to have this kind of stuff lying around). You may choose to use the motors you already have, rather than going on a wild goose chase for the other motors. So, these mo-tors now become a fixed specification, and you’ll need to compromise on your bot’s performance goals. That 20-mph robot you were planning might only go 10 mph now, and can only push half the weight you originally wanted.
Probably the biggest area of compromise comes with cost considerations. Say you found the ideal motors you want, but they cost $800 each and you need four of them for your four-wheel-drive bot. Like most beginners, you can’t really justify spend-ing $3,200 for motors. So you either find different motors, such as $100 cordless drill motors, or change the design from a four-wheel-drive bot to a two-wheel-drive bot.
Again, ideally, you should design the entire bot on paper or CAD before you start constructing it, although this usually isn’t as much fun. Most people find de-signing and building at the same time more enjoyable because it allows you to see the progression of the bot from day one. Other people enjoy the design process more than the actual building. If you enjoy building, team up with a good de-signer. If designing is your thing, then find yourself a good builder to partner with.
When your bot is completed, you should create a new set of drawings showing how the bot was actually built—especially all of the electrical wiring. These draw-ings will come in handy when you need to repair or improve the bot at later dates.
It’s easy to remember everything that went into building the bot when we first fin-ish building it. But we soon forget certain details, which can create problems when maintenance is needed. These as-built drawings will save you a lot of headaches down the road.
Design for Maintenance
Part of the whole design process for combat robots is the design for maintenance.
In competition, you have about half an hour to make any repairs to the bot. This really isn’t a lot of time. So you must design your bot to allow for rapid replace-ment of parts. This usually means there are more bolted-on components than welded-on components. You need to have quick access to the electronics and bat-teries so they can be replaced or recharged in a matter of minutes.
In competition, you have about half an hour to make any repairs to the bot. This really isn’t a lot of time. So you must design your bot to allow for rapid replace-ment of parts. This usually means there are more bolted-on components than welded-on components. You need to have quick access to the electronics and bat-teries so they can be replaced or recharged in a matter of minutes.