Common Robot Types
Most combat robots can be divided into a number of classifications. In general, you can use this information to predict the effectiveness of one bot against another.
The following is adapted from The Combat Robot Handbook, check it out for a more in-depth discussion of each bot type.
Vertical spinners are defined by having a weapon spin vertically, so that the cutting edge moves upwards or downwards towards the competing bot. Most vertical spinner weapons are circular, although it is not uncommon to see large bars, akin to a lawnmower blade.
Vertical spinners generally will have their weapon centered over the body. The weapon also commonly serves as a self-righting mechanism, as the bot's weapon is generally too tall to allow it to drive inverted.
There are two main disadvantages to vertical spinners. First, the weapon contact point is generally further away from the center of mass of the bot. While this can be beneficial in some scenarios as a means of keeping an opponent at bay, it also means that the moment of torque upon impact is much greater on your bot, leading to a high chance of it to go flying away as well. The second major limitation is that since the spinning weight has such a large radius, vertical spinners often struggle to move. They must overcome the gyroscopic forces of their weapon in able to effective move.
A vertical spinner is distinct from drum spinners in that the blade has a greater diameter than thickness.
Similar to vertical spinners, drum spinners have a single central weapon that spins to deliver upwards or downward strikes to the opponent. The main difference is that a drum spinner is much thicker and with a smaller radius than a vertical spinner. It is not uncommon for drum spinners to have the entirety of the front of the bot be the weapon.
With a smaller and lower down weapon, it is possible to build your bot low enough to the ground that being inverted is no problem; just have the wheels stick out both above and below the chassis.
Having the spinning weight of the weapon closer in reduces the moment as you spin, allowing you to spin up faster and reducing how much you are knocked back in a hit.
The downside to a drum spinner is that they tend to make for very heavy and hard to balance weapons. The most common profile for a drum weapon is a cylinder with a single tooth, so the center of mass is far away from the rotating axis. This leads to premature wearing of the bearings, pulleys, and motors.
Another limitation of drum spinners is that they are extremely ineffective against other drum spinners, since it will mostly end up being the weapons always in contact with each other.
Beater Bar Spinners
Beater bars, also sometimes called eggbeater spinners, are a variation on the drum spinner that is easier to manufacture and balance, but at a cost of having less mass behind each hit. Beater bars are usually cut from a flat piece of stock, and then have the teeth threaded into them.
Besides the advantages for manufacturability and balance, beater bars perform nearly identical to drum spinners.
Horizontal spinners are a class of bots that spin a blade or bar weapon horizontally, so it hits the opponent on the left or right side. Horizontal spinners can be split into 3 sub-classes, based on the vertical height of the weapon.
The first of these are undercutters. Undercutters mount their weapon very low to the ground, so that the blade impacts the opponent's wheels or undercarriage rather than their armor. This makes them extremely effective at disabling opponents, but the low weapon height makes them very susceptible to floor damage. Plus, if they are flipped, they now no longer have any of those benefits.
The second sub-class is center spinners, usually referred to as just bar spinners since they are usually bars instead of circular disks. Center spinners have their weapon mounted on the centerline of their bot, so the weapon is just as effective if they are flipped. This is the easiest sub-class of horizontal spinner to build, but also the most prone to inflicting self-damage, as most designs have the weapon spinning in part inside of the frame.
The third sub-class is overhead spinners. Overheads can attack the enemy from any angle and has no limitation on weapon size, since the weapon spins above the rest of the bot. The two major concerns with this style of bot are that it can only hit bots that are at least as tall as it, and they generally have to rely on spinning their weapon or bouncing off of other stuff as a self-righting mechanism.
Full Body Spinners
Full body spinners are a further evolution on horizontal spinners, where the spinning weapon fully envelops the bot, so that any contact with the bot is always against a weapon. This also puts the weapon, generally the hardest and heaviest piece of metal in the bot, between the enemy and all of your sensitive electronics. Some bots just spin a part of their exterior (called ring spinners) and some spit their entire exterior (called shell spinners).
The major limitation to full body spinners is that they are very hard to design. You have extremely limited space inside the internal diameter of your weapon, and you have to somehow drive the weapon somewhere besides the central axis.
A further evolution on this concept is the meltybrain. Meltybrain bots are extremely easy to design, as they do not have a weapon motor. Meltybrains work by driving the drive wheels in opposite directions, spinning the entire bot in place. While easy to design, meltybrains are incredibly hard to control, and it often times comes down to simple luck of your competitor getting hit as you flail around.
Flippers and Lifters
Flippers and lifters refer to two slightly different types of bots, that both use a spatula and lifting motion to attack. Flippers, usually powered by pneumatics, get under and throw their competitors, inflicting damage or hopefully having them land in an orientation they can't self-right from. Lifters use somewhat more controlled motion to pick up and pin a competing bot. While this does little actual damage, it can score points in a fight that goes to the judges.
Cutters and Saws
Cutters and saw bots refer to robots with a spinning weapon that is on an actuatable arm. The idea is that you grapple your opponent, and then bring down the spinning tool to try and cut through them. While these do make for an impressive show, they are generally not very effective, as they require precise alignment and a considerable amount of time to do enough damage to one spot for critical failure to occur.
Axes and Hammers
Axe bots and hammer bots are combat robots that use a tool on an arm to attack their competitor. Hammer bots do this with a large, blunt hammer to inflict general damage to the top of the competitor, which is generally the weakest part of a bot. Axe bots, by contrast, use a sharpened point moving at high speeds to try and pierce the top of the competitor, and hopefully hit a battery.
There are two different variants of crusher bots. The first and most common uses a pincer or otherwise sharpened beak to drive down and both pin and puncture a competitor. These bots are generally not very effective, as they need to hold the competitor for a long amount of time, and need a bit of luck to hit something critical as they close.
The second variant of crushers are known as compactor bots. Compactors use blunt force of closing metal or plastic plates to crush a bot. These are generally not very effective, as they require completely incapsulating the competitor and require a massively powerful motor to be able to crush anything.
Wedge bots do not have an active weapon, but rather drive under competitors with a wedge to hold them off the ground, disabling their movement. While wedge bots are not allowed at NHRL as a main bot, many teams run a small wedge bot in a multibot configuration to get under and immobilize the opponent, as the main bot attacks.
Flamethrower and Fire Bots
NHRL allows for bots that use fire, heat, or flames as their primary weapon. While these bots put on a cool show, they are generally not very effective. The operating principle is that you can try to melt or char a portion of the competitor's bot, such as the wiring harness or rubber/plastic wheels.