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While a powerful spinner is the most destructive form of kinetic-energy weapon in the competition, this destructiveness comes with a price. The powerful kinetic impacts that the spinner delivers are felt as much by it as by its opponent; many spinners have crippled the opposing robot only to be themselves knocked out by the same impact. A spinner needs to be built as ruggedly as possible to avoid this fate. Many of the fully enclosed shell-type spinners use rings of rollers on the inner frame to allow the spinner to ride smoothly even if it becomes bent or dented. A fully enclosed spinner has an additional difficulty not faced by other robots: when the weapon is running, it can be difficult for the robot’s driver to see which way the base inside is facing! Methods of dealing with this include having a tail trailing out underneath the shell, having a non-rotating flag or arrow sticking up through the center of the shell, making part of the spinning shell out of transparent materials, or cutting windows in the shell to allow the interior to be partially visible. The reaction torque of spinning the shell will produce a strong turning force on the base of the robot, which will make the bot want to swerve to the side when driving. A four-wheeled base is recommended to give some straight-line stability. Many spinner drivers also use R/C helicopter rate gyroscopes in their control elec- tronics to compensate for the effects. For optimum damage, the spinner weapon should be large and should have its mass concentrated as much as possible at the outside of its radius. Many spinner weapons are made of disks or domes with weights at the edges and holes in the middle, to maximize the rotary inertia of the weapon. Of course, more inertia in the weapon means a greater spin-up time. Strategy Ideally, a spinner wants to knock out its opponent in as few hits as possible. A spinner’s worst possible opponent is a solidly built ram or wedge, which can take repeated impacts until the spinner breaks itself. A high-speed collision with a wedge can cause some spinners to flip themselves over. Spinners fare better against lifters, clamp bots, or hammers—exposed weapon parts that can be bent or broken off of an opponent help a spinner win. Saw Bots The saw bot was first used in The Master (Robot Wars, 1994). Examples of saw bots include Ankle Biter and Village Idiot. Saw bots feature an abrasive or toothed disk that is spun by a powerful motor, which is intended to cut or rip the opponent on contact. 222 Build Your Own Combat Robot Chapter 10: Weapons Systems for Your Robot 223 Saw Design Now increasingly rare, the saw was tried many times in the early days of robot combat, usually with little success. The idea of disabling the opponent by slicing it apart has proven to be a difficult challenge because the materials most modern combat robots are made of take too much time to cut, even under controlled cir - cumstances, let alone when the target is actively trying to get away from the saw blade. The concept has been largely abandoned, aside from a few brave robots that use saws in combination with other attack styles. Combat trials have shown that the best saw blades to use are the emergency rescue blades used to rescue accident and building collapse victims. Thick steel disks coated around the edge with hard abrasive make these blades able to cut a wide variety of metallic and non-metallic materials quickly—just the thing for a combat situation. They are, however, heavy, expensive, and available only through certain specialty dealers, and they require a seriously powerful motor to be used to full effect. Figure 10-9 shows some examples. FIGURE 10-9 Robots wielding saw blades. Saw blades, other than the emergency type, have not proven to be effective. Abrasive disks are nearly useless against soft materials like plastics, wood, or com - posites, and they easily shatter on impact. Toothed wood-cutting blades cut softer material nicely, but they stall on metals. Milling saws are heavy, can shatter on hard impacts, and usually knock the opponent away rather than cutting into it. Damage from a saw does not come in the form of one or two big hits, but from many small gashes and cuts. The saw motor should have enough torque to keep the saw from stalling, and it should have speed of a few thousand RPM. More mass in the saw blades will help optimize damage on initial contact, keeping the weapon from stalling instantly. The best saw weapons act more like spinners than saws, storing up a lot of inertia in the weapon to deliver on contact with the opponent. Strategy The saw, by itself, is not an effective means of disabling an opponent. Unless already disabled, your target will not stand still and give your bot the time to cut into it, so the most a saw is likely to do is leave scratches and shallow cuts while throwing sparks and dust. Still, while rarely fatal to the opponent, a powerful saw and the cosmetic damage it leaves can impress the audience and judges enough to give you the win in a close match. Saws are best combined with an attack strategy that gives you the dominance over the opponent’s mobility—a powerful wedge, ram, or even a lifter or clamp bot can prevent the opponent from dominating the match and give the saw weapon time to score points by inflicting visible damage. Against a spinner, a saw may be useless, however, as the exposed saw blade is usually the first thing to break when struck by a serious weapon. Vertical Spinner This type of bot was first used on Nightmare (BattleBots, 1999). Other spinner bots include Backlash, Nightmare, Greenspan, and Garm. Vertical spinner bots include a heavy disk or bar that spins vertically in front of the robot, usually spin - ning such that the front of the spinner is moving upward, so that on contact the opponent not only receives a massive blow but is lifted into the air from the impact. Vertical Spinner Design The vertical spinner takes the basic spinner concept and turns it on its side. Instead of having a spinning blade or shell on top of the robot, the vertical spinner sets the mass spinning about a horizontal axis, almost always with the exposed front of the spinner moving upward. When it strikes an opponent, the impact force pushes the opposing robot upward, often flipping it over or subjecting it to a hard impact with the floor when it lands. The recoil force on the vertical spinner merely pushes 224 Build Your Own Combat Robot it down against the floor, rather than flinging it sideways, as can happen with a conventional spinner. Figure 10-10 shows a vertical spinning robot. While the weapon can be much more effective than a standard horizontal spin - ner, the vertical spinner trades off improved offense with a greatly weakened de - fense. While a standard spinner can be built to cover the robot’s body completely, such that an opponent cannot help but be hit by the weapon on any contact, the vertical spinner’s narrow disk must be carefully lined up on its target. The large disk gives the vertical spinner a dangerously high center of gravity, requiring a large, wide body to support it, which makes the vertical spinner vulnerable to at - tacks from the sides or rear. Spinning the disk will generate significant gyroscopic effects every time the ro - bot turns, requiring widely set drive wheels and a slow turn speed to keep the robot from flipping itself over when turning. The vertical spinner also suffers the same self-inflicted impacts as the standard spinners. While the impacts are downward and the floor helps brace the robot in place, vertical spinners have been destroyed by their own weapon impacts. As with the spinner, the optimum form of the vertical spinner will be a diskwith the weight concentrated at the edges. Vertical spinners have the additional prop- erty of hurling their opponents into the air on solid hits, doing additional damage when the opposing robot crashes back into the floor. Chapter 10: Weapons Systems for Your Robot 225 FIGURE 10-10 Robot with a vertical spinning disk/blade. 226 Build Your Own Combat Robot Strategy Vertical spinners are good against any opponent that cannot disable them quickly or outmaneuver them to avoid being struck by their weapon. A slowly moving lifter, clamp bot, or rammer will be an easy target for a vertical spinner. A wedge may be a tricky target for a vertical spinner, especially if cone or pyramid shaped, because the spinner blade works best when it can catch on an edge on the target robot. A fast-moving wedge or lifter that outmaneuvers a vertical spinner can be a very difficult opponent. A fight between a vertical and a horizontal spinner is usually short and violent, and can go either way. If the vertical spinner manages to bring its weapon into contact with the horizontal spinner’s body, the resulting impact can damage the horizontal spinner’s mechanism and disable it or even—in extreme cases—flip over the horizontal spinner. The vertical spinner can also take significant damage from the hit; and if the horizontal spinner is able to maneuver to strike at the verti - cal spinner’s exposed drive wheels, it stands a chance of ripping them clean off and winning the fight without taking any direct hits. Drum Bots The drum was first used on Gut Rip (Robot Wars 1996). Other drum bots include Little Drummer Boy and El Diablo. Drum bots feature a wide drum with protruding, spinning teeth or blades that are mounted on a horizontal axis across the front of the robot. Like the vertical spinner, the front of the drum spins upward to lift the opponent on contact. Drum Design The design is similar to the vertical spinner; but, instead of a narrow disk or bar weapon, the drum uses a horizontal cylinder—usually covering the entire front of the robot, studded with teeth and spinning with the front traveling upward. While the drum shape carries a lot less rotational inertia than a wider disk, the design makes up for it with improved durability and a more-compact shape. Less inertia in the rotor makes for weaker impacts, but it also makes for faster spin-up time and less impact force felt by the rest of the robot. A drum robot can typically hit an opponent repeatedly in a short period of time; and with a lower center of gravity and less gyroscopic effect to fight, it can be faster and much more nimble than a vertical spinner. Drum designs are also much more amenable to being run upside down, which is usually accomplished by making the drum diameter just less than the wheel diameter and using a reversible motor to spin the drum, so that the weapon can operate equally well either right-side-up or upside down. Drum robots are typically made in a four-wheeled configuration, with a roughly square overall shape. The wider weapon doesn’t need much careful aiming to use effectively; and because the impacts of the weapon tend to lift the target ro - bot into the air, the drum functions well in a ramming/pushing mode—repeatedly kicking its opponent across the arena with a combination of weapon hits and drive power. Figure 10-11 shows a drum robot. The vulnerable parts of the drum are the drive mechanism and support struc - ture. The simplest and most common design is to support the drum with bearing blocks on either side and to use a chain drive to run the drum from a motor inside the main body of the bot. This method works until a strong blow to either front corner breaks a support arm, cracks a bearing block, or dislocates the chain. Hiding the drive motor inside the drum is a more durable but much trickier option. Because the drum will be subjected to a major downward impact every time it strikes an opponent, support arms or wheels under the drum weapon to keep it from being driven into the arena floor are a good idea. Many drums also have some kind of ramp or scoop built into the drum supports, so that wedges will be fed up into the drum—rather than getting under it without being hit. The drum doesn’t pack nearly as much inertia in its weapon as the vertical spin- ner. What inertia it does have can be maximized by constructing the drum with as Chapter 10: Weapons Systems for Your Robot 227 FIGURE 10-11 Robot with a spinning drum in front of the robot. wide of a diameter as practical. A wide drum with short teeth welded to it will pack more of an impact than a thin shaft with larger blades. Strategy Drums lend themselves to an aggressive driving style; the fast weapon spin-up and ability to upset an opponent’s footing on a good hit mean this style of robot can take control of the match and keep the opponent on the defensive. Robots that don’t do much damage quickly or need time to set up a controlling move, such as thwack bots or lifters, can usually be beaten by a good drum. The bane of the drum is the wedge. A wedge’s sloped front and often sloped sides don’t offer a good surface for the drum’s weapon to catch. A well-designed, powerful wedge will have more of its weight budget devoted to drive power than the drum; and if the drum’s weapon cannot catch on the wedge to damage and flip it up, the wedge will have the advantage. In a fight between a drum and a spinner, the battle usually will hinge on whether the drum’s weapon drive and support structure can hold together long enough for the spinner to be disabled. The drum’s weapon can kick a spinner into the air, breaking its traction and spinning it around under the recoil of it’s own weapon, but the drum weapon is going to take a significant impact from the force—possibly disabling it or even tearing it free from its mounts. Hammer Bots The hammer was first used on Thor (Robot Wars, 1995). The Judge, Killerhurtz, Frenzy, Deadblow, and Mortis are examples of hammer bots. Hammer bots feature hammers, axes, picks, or mace weapons on powered overhead arms, and are designed to inflict repeated blows on an opponent’s top armor or exposed wheels. Hammer Design Like a spinner, a hammer bot accelerates an impact weapon, storing kinetic energy that is all released into the opponent in an instant. While the spinner can take its time storing energy in its weapon, the hammer design must get its weapon up to speed in a single swing, dumping its energy into the weapon in less than a second. This disadvantage is offset by the hammer’s ability to control the timing and placing of its hits, strike repeatedly in a short period of time, and use its weapon even if pinned or lifted. Most hammer weapons can also be used as self-righting mechanisms if the hammer bot is flipped. Figure 10-12 shows the schematic. Most hammer weapons are pneumatically driven. The most common and easi - est method is to attach a pneumatic cylinder that pushes the hammer down from 228 Build Your Own Combat Robot Chapter 10: Weapons Systems for Your Robot 229 behind. This limits the hammer’s travel to at most 90 degrees, and less if you are striking a tall robot. This isn’t much room to get the hammer up to full speed and will mean that your weapon will strike only flat robots with its full power. A better option is to use a mechanism that allows the hammer to travel a full 180 degrees, permitting it to get up to full speed before it impacts. This can be accomplished with a pneumatically driven rack-and-pinion mechanism driving the hammer arm, or by using a pneumatic cylinder to pull a chain wrapped around a sprocket connected to the hammer arm. Figure 10-13 shows a photo of Deadblow, one of the fastest rapid-firing hammer robots to compete in BattleBots. Whichever mechanism is used, the limiting factor in a pneumatic hammer’s speed will be the rate at which you can make the working gas flow from your storage tank into your driving cylinder. As the pressure regulator is a major bottleneck, some pneumatic hammer bots have huge low-pressure reservoirs downstream of the regulator to provide the high flow rates that the hammer needs. Other bots use massively large-bore tubing and valves to minimize flow resistance in the pneu - matic lines. High-pressure systems that run gas straight out of a carbon dioxide tank with no pressure regulation can provide extremely high rates of force deliv - ery, but these systems are expensive, dangerous, and difficult to build. Carbon dioxide absorbs a lot of heat from its environment as it expands from liquid to gas, which means that a CO 2 tank called upon to provide gas for many hammer shots in a short period of time can freeze up and become too cold to de - liver gas quickly enough to keep the weapon running. To get around this, some FIGURE 10-12 Schematic of hammer mechanisms. builders use high-pressure air or nitrogen, which do not have to change state from liquid to gas. This gets around the problem of the tanks freezing up, but it doesn’t store nearly as much energy in the same space and requires huge tanks to run a hammer for an entire match. Another option is to drive the hammer with an electric motor. This makes it easy to give the weapon 180 degrees or more of travel, allowing it to reach full speed before hitting the target. Gearing should be optimized for maximum speed at impact, taking into account that with too low a gear ratio, the motor won’t have enough torque to get up to speed, while too high a ratio will mean that your ham - mer will reach its top speed too early and not do as much damage as it should. Problems of both speed and torque can be solved by choosing the most powerful drive motor you can for the mechanism. Some hammer robots have used a crankshaft mechanism to produce recipro - cating hammer motion from a continuously turning drive motor. When consider - ing this kind of mechanism, you should keep in mind two things: First, you want the hammer moving at maximum speed when it strikes the opponent; many sim - ple crankshaft mechanisms will have the hammer traveling at top speed only in the middle of the stroke. Second, if the hammer’s motion is interrupted mid-stroke, it should have some way of reversing and striking again without stalling or having to lift the entire robot off the ground. Hydraulic-powered hammers have also been built. Hydraulics can provide tre - mendous force that can accelerate a hammer very quickly, but most hydraulic systems respond rather slowly and are not ideal for the high speeds required for rapid-fire striking a good hammer system needs. Building a hammer mechanism 230 Build Your Own Combat Robot FIGURE 10-13 Deadblow, a 114-pound pneumatic hammer bot. (courtesy of Grant Imahara) Chapter 10: Weapons Systems for Your Robot 231 with a hydraulic drive will require a powerful motor and expensive, high flow-rate valves and tubing. Some builders have experimented with using a large spring to power the hammer and a high-torque motor or linear actuator to crank the hammer back and latch it after firing. While this can give a powerful hammer action, the increased reload time makes the concept questionable. A hammer that takes more than 5 seconds between shots may never manage to hit its opponent more than once or twice in an entire match. For optimum results, increase the hammer velocity as much as possible. Re - member that your hammer may strike its opponent only partway through its stroke, so design for it to do most of its acceleration at the beginning of its travel. Strategy Even the strongest hammer bots have trouble consistently disabling opponents with their hammers. A hammer bot’s best opponent is one with weak top armor or a fragile frame. Barring that scenario, a hammer bot should try to strike as many blows on the opponent as possible while avoiding being disabled. A hammer stands a good chance against a thwack bot, wedge, ram, or saw-wielding robot, because those designs won’t be able to disable the hammer quickly and the ham- mer can get a lot of good hits in. Against a crusher, a hammer bot will have a hard time; the hammer may need to strike many blows to affect the crusher, but the crusher needs to get lucky only once. Any good hammer bot should be able to self-right quickly with its weapon, which reduces the threat from lifters and launchers. Fighting a spinner with a hammer is often disastrous for the hammer, because the spinner’s weapon will be nearly impossible for the hammer arm to avoid, and striking the active spinner with the hammer arm will likely result in a bent or even torn-off weapon! Crusher Bots The crusher was first used on Munch (Robot Wars, 1996). Some examples of crusher bots include World Peace, Razer, Jaws of Death, and Fang. Crushers feature a large, heavily reinforced claw, usually hydraulically powered and capable of closing with several tons of force to crush or pierce the opposing robot. Crusher Design Mechanically the most challenging concept to build, crushers use powerful claws to pierce and crush the opponent. Most crusher designs use hydraulics to achieve the incredibly high forces needed to pierce armor, although ball-screw linear actu - ator designs have also been used. [...]... that is attached to the underside of your robot s bumpers or armor When another robot hits your robot, the bump switches will tell the robot that it was hit One implementation of a bump switch is to place it on the sides and the back of your robot When your robot is moving forward and the bump switches indicate that something is hitting the side of your robot, your robot can initiate an automatic spin... semiautonomous target tracking With this type of system, you can simply drive your robot close to FIGURE 11-6 Semiautonomous weapons systems diagram 251 252 Build Your Own Combat Robot your opponent, and your robot s sensors will lock onto the opponent and take over the driving You maintain complete control of the weapon and let your robot push the opponent around the ring, you can have all the fun smashing... and FIGURE 11 -7 Semiautonomous target-trackingsystem block diagram Chapter 11: Autonomous Robots if your opponent moves too close, your robot will back away from it Using this type of system, you can keep your opponent inside the “sweet spot” of your robot s weapon’s strike zone This type of system can be advantageous against the aggressive spinning robots You can automatically keep your distance... is close to your robot But this robot still needed the human operator’s eyes to get the job done Fully Autonomous Robot Class In the early years of robot combat at Robot Wars, a fully autonomous class of combat robots existed To account for safety, in 1996, specific rules were written about autonomous robots by Bob Gross The key element to these rules is the use of an infrared beacon The robots must... detect the opponent or both detectors do not detect the opponent, drive forward You manually drive your robot up to your opponent until it is within your robot s crossing beams’ reach, and then you can enable the semiautonomous tracking system and your robot will close in on your opponent on its own Figure 11 -7 shows a simplified schematic of this type of control system As with the semiautonomous weapons... can create much more sophisticated robotics behaviors that don’t rely on constant human input to keep the robot going The most robust robots typically have the most robust sensor input dictating the behavior of the robot S emiautonomous Target and Weapon Tracking When you begin competing in robot combat matches, you will discover that it is a lot harder to get your robot positioned to deliver the deadly... finally get your robot positioned and the opponent is in the sweet spot for the attack, you could miss an opportunity because it took you too long to flip the attack trigger on your remote control This sort of predicament is frustrating to the beginning combat warrior If you look at videos of past combat events, you will notice that missing the opponent is a common problem for many beginning robot combatants... this type of switch Gravity is used to hold the ball down on the bottom contact When the FIGURE 11-5 Mechanical tilt switch 2 47 248 Build Your Own Combat Robot tube rotates past horizontal, the ball will roll off the contact, thus opening the circuit The figure shows a bracket at some angle The smaller the angle becomes, the more sensitive the robot becomes to angular tilting Bump Sensors A bump sensor... walk up to the robot to shut it off to take it into the pits for repairs? If the robot is programmed to attack any robot that gets near it, how will it tell the difference between a human and another robot? It probably won’t, and it will attack any human, or robot, that approaches Because of this potential danger, some contests prohibit fully autonomous robots For safety purposes autonomous robots must... safety purposes autonomous robots must have a remote control kill switch to remotely shut the robot down at the end of a match or in emergency situations 253 254 Build Your Own Combat Robot quency, so different beacons could be distinguished between each other The four different modulation frequencies were 550 Hz, 70 0 Hz, 850 Hz, and 1000 Hz The reason for using the 40-kHz carrier frequency was so that . contact. 222 Build Your Own Combat Robot Chapter 10: Weapons Systems for Your Robot 223 Saw Design Now increasingly rare, the saw was tried many times in the early days of robot combat, usually. the opposing robot crashes back into the floor. Chapter 10: Weapons Systems for Your Robot 225 FIGURE 10-10 Robot with a vertical spinning disk/blade. 226 Build Your Own Combat Robot Strategy Vertical. hammer down from 228 Build Your Own Combat Robot Chapter 10: Weapons Systems for Your Robot 229 behind. This limits the hammer’s travel to at most 90 degrees, and less if you are striking a tall robot.