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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 disk with

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.