Intro to Fighting Robots

Fighting Robot Basics

This is intended to be a basic introduction to the main ingredients required to make a fighting robot and will occasionally be expanded upon. If you have any questions, feel free to send me an email. Images illustrating each section will be added over time.

Useful resources:

Rules-
Robot Fighting League
NERC -Northeast US
Robowars -Austrailia
Fighting Robot Association -UK

Components-
Fingertech Robotics -Small robots
Equals Zero Designs -RageBridge and Dewalt gearbox
Holmes Hobbies -BR-XL motor controller
The Robot Marketplace -Almost everything
McMaster-Carr -Hardware and raw materials
Hobby King -Cheap things from China

Kits-
Kitbots -Small robot kits & parts
BattleKits -Large robot kits
The Robot Marketplace -Kit section

Robot combat community sites-
Robot Fighting League Forum
NERC Forum
Fighting Robot Association Forum
Robowars Forum
Unofficial BOTSIQ forum

Reference and tools-
Killerbotics Tools -Useful info and drivetrain calculator
Riobotz Combat Robot Guide -Most in depth guide to robot combat available

Weight Classes

The common weight classes in North America today are:

150g
1lb
1kg (Canadian, mainly)
3lb
6lb (limited)
12lb
15lb (botsIQ/school competitions)
30lb
30lb Sportsman (NERC, primarily)
60lb
120lb
220lb
340lb (no longer active)

Radio System

When selecting a radio system, the first thing you must do is confirm that the system will failsafe on all used channels. Fail safe means that if the signal to the receiver is lost, all drive and weapon systems will return to a non-active state. Any system incapable of this function will not be allowed to pass safety. 2.4 GHz radio systems are increasingly common and often required at events. There are a wide range of products available that meet the failsafe requirements and 2.4 GHz suggestion. If you’re not sure that a system will failsafe properly, ask the merchant or manufacturer. The Robot Marketplace often will list if a system or component will failsafe properly on the product description.

Kill Switches

Commercial Switches

Being able to safely turn your robot on and off is another requirement to compete. The Whyachi MS-XX series and the Hella switch are two good commercial options, both of which are available on The Robot Marketplace

Home Made

In addition to commercial switches, there are some styles of power switches that can be made at home. The most common involves using a plug to add a removable loop of wire between the battery and motor controllers. Using this method means you will physically remove part of the circuit to power off the robot.

Motor Control

There are several methods commonly used to control electric motors in robot combat. For full proportional speed control, an electronic speed controller (ESC) is generally the most reliable option. There are a wide range of ESCs available for robots ranging from 150g to 220lb. The key is to find a controller that is rated for your desired voltage or higher and can handle the current draw of the motors. The torque/AH calculator at Killerbotics.com has many common drive motors and can be used to estimate stall and wheel spin amperage.

For motors that only need on/off functionality, contactors/DC solenoids can be used in conjunction with RC switches for more power handling capabilities at the cost of precise control.

Motor Selection

There are two main types of motors available, brushed and brushless. Brushed DC motors have been used in robot combat since the beginning. They’re a bit bulky, tend to spin at relatively low RPM and have great starting torque. Brushless motors have recently become the go to option for high powered weapon, and occasionally drive systems. Brushless motors tend to have a higher power to weight ratio, much higher RPM but often suffer from “cogging” when geared with low reduction and heavy attachments. Brushless drive systems are uncommon as there are very few controllers available that give quick, proportional forward and reverse control, and the high RPM’s make gearing systems more difficult than with brushed motors.

Drive System

For a first build, wheels with tank style steering are the simplest option. Tracks and walking systems can be built, but on your first build, getting something working reliably should be a focus. The two main wheeled options are 2wd and anything greater than that, though usually in multiples of two. Two wheel drive robots will have two powered points of contact with the ground, and short of a balancing robot, this means at least one non powered point of contact will exist. This can either be a piece of chassis/armor dragging on the ground, a skid or a caster. The best option will depend on the exact design of the robot and what arena it will compete in. Robots with greater than two driven wheels will likely have all points of contact with the ground powered, with the exception of hinged components that are meant to stay in constant contact with the ground.

Chassis Construction

Chassis construction generally takes one of a few different routes. The first is an internal frame with armor attached to it, the second uses the frame members as armor, often with connected plates of material forming the structure, and the third is unibody construction, where the majority of the frame and armor are cut from a single piece of material.

Building a chassis using an internal frame with armor panels mounted to it tends to be the heaviest of the three options, though often will be the most durable and easiest to repair as the portions of the armor most likely to be damaged are easier to remove from the rest of the robot. These frames typically involve a welded frame with armor bolted to it.

Frame as armor construction is generally in the middle when looking at strength vs. weight. By reducing frame and armor into a single part, you can reduce the size of the machine and use relatively thick materials in areas likely to come into contact with weapons. Frames like this are more often than not bolted together.

Unibody construction will typically be the strongest per pound, however it is also the most complicated to manufacture, as all features will need to be added to a single piece of material. This often involves repositioning the work piece many times during the construction process. Care must be taken to avoid misalignment of holes as the work piece is moved. The good strength to weight ratio, the best of the three mentioned, is due to the reduced need for fasteners to hold the chassis together and the lack of areas only held on by hardware.

Common materials

Steel and titanium are the go to materials when you need both stiffness and strength. These metals are difficult to cut and bend relative to aluminum and magnesium, making them better at handling most forms of attack. Compared to the other listed materials, these are the densest options available, with steel being generally the strongest, but also the heaviest, and titanium having a much better strength to weight ratio but being expensive and difficult to work with.

Aluminum

Aluminum is a fairly light metal, easy to work with and isn’t too expensive. There are many grades of aluminum available, but 6061, 2024 and 7075 are the most common in robot combat applications.

Magnesium

Magnesium is the lightest metal listed. Magnesium is fairly easy to machine, however heat control is a must as it burns energetically if it is allowed to get hot enough. AZ31b magnesium has a higher tensile strength than aluminum, which makes it a great material for armor if you can afford the cost, which rivals titanium.

Plastics

There is a wide range of plastic materials available and an entire guide could be written on them. The most common plastics in robot combat are polycarbonate, nylon, UHMW polyethylene, and delrin.

Composites

Composite materials come in two forms, pre-made parts and raw fabric. The pre-made parts are often used as armor panels when weight is a serious concern. When used properly they can be as good as some metals, however their limitations must be kept in mind. Different composites will have specific types of applications they are good for. Some are better in tension and some are better in compression. This is due to what the composite is made of. The parts, commercial or diy, are a mix of the fabric, (Kevlar, carbon fiber, fiberglass, etc…) and a resin. The fabrics generally perform well in tension, regularly exceeding the tensile strength of popular metals and the resin handles the compressive loads.

Weapon Examples

Non-Kinetic Energy Weapons

Rammer

Ramming robots are the most basic design in robot combat. A ramming robot relies purely on the strength and power for success. Ramming robots often incorporate spikes or heavy chunks of metal on the front of the robot. Spikes on a ramming robot are normally intended to penetrate the armor of the opposing robot. Ramming robots with simple metal chunks on the front of the robot use their drive power to drive their opponents into the walls or any hazards in the arena. Strong rammers are sometimes capable of breaking spinning weapons. They all have one thing in common, they are very hard to immobilize. They are often invertible, durable, and have powerful drive systems.

Wedge

Wedge robots are similar to ramming robots. They share the need for a powerful drive system, a strong chassis, and good armor. Wedge robots are among the most common types of robot in robot combat today. Many robots incorporate a wedge into the design in some form. For some, it’s the backup plan if the weapon fails. For other robots, the wedge acts as part of the weapon, be it leading into spinning blades, or a hiding place for a powerful arm. These robots are all about mechanical advantage. They get under their opponent and use their drive power to flip them or shove them at high speeds into an obstacle like a rammer.

Lifter

Lifting robots can be viewed as the next step up from a wedge robot. They perform essentially the same function. They both make the drive system of the other robot ineffective. There are a few different methods of constructing lifting arms.

The most basic is pushing or rotating a single hinged piece of metal. It is very effective in its simplicity. For this style of lifting arm, linear actuators are often used. Linear actuators act like pneumatic pistons, but slower and in an often lighter package.

Another popular lifting system uses a four bar linkage. This system allows the bar to lift and push at the same time. It also lets the arm tuck nicely back into a flat chassis. This system has proven extremely effective when built properly.

Some lifters drive the arms with an electric motor. With that system, the arm is attached to a rotating shaft. The shaft has a sprocket or gear on it which is driven by an electric motor. These systems require heavy gear reduction to be effective.

Hydraulic lifting arms have sometimes been used, but are uncommon in combat robotics. They are often too heavy and slow for most applications of this nature. Hydraulics are better suited for systems that require large amounts of torque and not much speed.

Lifting arms require a very strong drive and chassis system to be effective. If it cannot take the abuse a more aggressive weapon can deliver while the lifter is trying to get under its opponent, it will not be successful.

Flipper

Flipping robots are essentially lifters run at much higher speeds. Flipping robots normally use pneumatics to power their arms due to the high flow rates achievable in pneumatic systems. Pneumatics can be used in any lifting system that can be operated by an extending rod. Flipping robots are able to throw their opponents into the air, possibly dislodging vital components or causing them to land in a manner that would prevent them from driving. Flipping mechanism normally require more weight than a lifter, as more power is needed to send a robot into the air than to tip it.

A prominent flipping system in European robots has the piston attached to a hinged plate that fires out of a wedge shaped chassis. The plate is hinged at the bottom, which causes the swing of the plate to not only lift the opponent but toss it away from the flipper robot.

Another common flipping arm is hinged at the back of the robot. It extends to the front, and then bends down to meet the ground with some means of getting under another robot attached. The pneumatic piston is either mounted vertically or in a position that when the piston has reached maximum extension it will be vertical. This reduces the loss of force due to leverage some other systems have, allowing for a very powerful throw. These flipping arms tend to throw the opponent vertically and often spinning into the air.

Grabber

Grabbing robots are a variation of the basic lifter. Grabbing robots use some sort of device to get a hold of their opponent which allows them to manipulate the opposing robot in ways that other types are not able to. While some grabbing robots do not use a lifting mechanism in conjunction with their grabbing mechanism the two work together well.

Most arenas used today do not have dangerous hazards in them, but grabbers could still be used to remove your opponent from a match by putting them over an arena barrier or into a pit.

Grabbers are a good option against many opponents in the right arena. They do have one major weakness, however. If they face a robot with a spinning weapon mounted in an area the grabber tries to pass through, there is a very good chance that their grabbing mechanism will be forcefully removed from the rest of the robot, making its primary mode of combat inoperable.

Crusher

Crushing weapons can be very devastating when used properly. They are not nearly as common as spinning or flipping weapons, but are on par with them when you look at damage potential and combat effectiveness.

Crushing arms are normally powered by hydraulic systems or high torque linear actuators. They tend to be slow, but extremely powerful. The goal of a crusher is to penetrate the armor of its opponent and dig the arm into some vital component of the opponent. Even if, after achieving penetration, nothing vital was hit, they still have a very firm grasp on their opponent. They can take them into any arena hazards or just drive them into the wall.

An effective crushing robot needs to have an agile drive system, a solid chassis and a strong arm. Due to the nature of the crushing robot, it needs to be able to get to the weak points on its opponents to be effective. The forces that are put into the chassis by the crushing arm are enough to warp a weak frame. A solid frame for the area that this force is transmitted into is vital.

Kinetic Energy Weapons

Hammer

Hammer robots have a many options when determining how to operate their hammer. Many different power sources are capable of powering an effective hammer.

The most basic method of actuating a hammer is to directly attach the piston to the hammer arm. This system makes it difficult to get a large swing angle but allows for a light weapon drive. This method has been used on many top hammer robots. The simplicity of this system makes it an easy hammer design to start with.

Rack and pinion hammer systems are somewhat heavier, but have a major advantage over them. These hammers can swing 180 degrees or more. The only rotational limit is the rack and pinion setup itself and the stroke of the piston pulling the rack. Adjustment of the gears in the rack allow for precise control of the arms swing.

Spring fired hammers use powerful coiled springs to shoot the hammer downward onto the opponent, then a heavily geared down electric motor to retract the hammer and ready it for the next swing. The spring can generate a great amount of power, but this weapon system is much slower than many of the other options for powering a hammer weapon.

Running the hammer directly off a motor is a simple method for making a hammer robot. Many of these systems are chain driven to achieve the proper speed and reduce the stress on the shaft of the motor driving it. Motor driven hammers tend to be fast but not as powerful as pneumatic hammers.

Thwack

There are two types of ‘thwack’ robots. One is a horizontal thwack robot. The other is an overhead thwack robot. Both types have been effective in combat, but horizontal thwackbots are more common as they tend to be easier to make.

Overhead thwack robots have the entire main body of the robot rotate with the hammer. This means that the majority of the mass must be contained within the diameter of the wheels. The striking object tends to be light because a heavy weapon would be much harder to flip over the top of the robot. Properly balancing the rotating body of the robot is essential to getting a good swing. Swinging the weapon is achieved by quickly reversing the direction of travel and using that torque to rotate the body 180 degrees.

The other type of thwack robot spins its entire body horizontally to cause damage. The impact points on the robot can be connected directly to the body of the robot or a mass can be attached to the end of a pole. Both methods have been effective in the past. The main difficulty with this design is that translational movement while the weapon is active is difficult. There are solutions to this, though. Most systems that attempt to fix this problem rapidly adjust the speed of individual wheels to cause it to slowly move in the desired direction.

Vertical

Vertical spinners come mostly in two varieties, bar and disk. Both do basically the same thing. The idea with a vertical spinner is to use the ground to your advantage. When a spinning object hits a robot, half the energy goes to each robot. Vertical disks use the ground to absorb that energy while the opponent only has its weight to resist the force. Vertical spinners require a lot of strength in the frame that supports the weapon to avoid damage during impacts. Many vertical spinners have a support going down from the shaft of the spinning disk to help absorb the impact.

Vertical spinners are prone to gyroscopic issues when turning. If you try to turn too quickly with a vertical spinner, it may tip to one side. You risk either flipping over or losing traction as the wheels are lifted off the ground. The hazard here is that when you are doing this, the other robot is able to better position itself for a counter attack. Vertical spinners tend to have wide drive systems to counteract this force.

Drum

Drum weapons are the cousin of the vertical disk. Unlike vertical disks, drums tend to have a fairly small diameter. They are also normally very wide, often covering the majority of one side of a robot. Gyroscopic forces become less of an issue with the drum design. They also have a much wider impact area. Drums are often spun at a higher rpm than other spinners. Drum robots don’t rely on one big hit. Drums are meant to get to speed quickly and hit many times in rapid succession.

A common drum variant, referred to as an ‘eggbeater’ removes the drum portion of the design, using just the impact bars and supports in the structure of the weapon.

Horizontal

The horizontal spinner is a wide category. It includes shell spinners, overhead spinners, front mounted spinners, and undercutters.

Shell spinners have a rotating mass that surrounds the chassis of the robot. These spinners develop a high amount of kinetic energy when spinning due to the large mass of the spinning object. The shells also double as a kinetic armor when the weapon is operational. Shell spinners are most effective when the shell is short in height. A low center of gravity keeps them stable after powerful impacts.

Overhead spinners normally use bars. This weapon is not as powerful as a shell spinner, but it is easier to build and weighs less. The weight savings allow for a stronger drive system or frame. The simplicity makes it an easier project for a new robot builder. These weapons, when used right, can be extremely effective.

Front mounted spinning weapons are almost identical to overhead spinners. Instead of having the blade on the top of the robot, it is mounted into a frame that comes out one side of the robot. This allows the blade to be lower to the ground and the robot that wields it to be taller without losing effectiveness.

Undercutters do just what the name implies. The idea with this weapon is to remove the wheels and anything else sticking out the bottom of the opposing robot. Undercutter blades ride close to the ground, which makes them difficult to avoid in a match. The blades often have a material beneath the bar to prevent them from hitting the arena floor.

All horizontal spinners have problems with over and under-steering. When you spin a large mass at a high velocity it causes the chassis to want to rotate. The rotation of the weapon will cause the robot to turn much faster in one direction and have trouble turning the other. It will also have some difficulties driving in a straight line.