Designing your first combat robot

When designing your first robot, you need to answer some very critical questions, and you need to answer them truthfully.

What weight class should the robot be?

This needs to be your first question. The answer depends on the following criteria:
Choosing the proper weight class will add bounds to the answers to the next few questions. When answering them, make sure to ensure that you aren't changing your weight class accidently, e.g. designing for the 55 pound class then ending up with a 75 pound robot. While it is possible to compete with it in the 110 pound class, you are lacking in 35 pounds that you could have designed to use if you had chosen the 110 pound class to begin with.

How will the robot move?

Moving is a must. If a robot fails to move, the robot is declared dead, and loses the match. As such, a robust and adequate drive train is a must. Likewise, this is one of the largest and most complicated parts of your design process, and ample discussion and explanation will follow below.

Your main design decision here is whether or not your robot will utilize wheeled movement or non-wheeled movement (i.e. legged movement, "dragging" movement, etc.). Tracks can be considered as a form of wheeled movement, as they are most commonly driven by a wheeled movement.

Once you know how your robot is going to move, you then have to engineer the necessary drive system. For your first robot, you should use a simple wheeled movement, so that will be the system we shall describe here.

There are two different types of wheeled movement drive systems that are prevalent in Robot Combat. The first is referred to as "tank-steer" systems. This is where one motor drives each wheel in a two-wheel drive system. To turn, a different amount of power is provided to each wheel. If the right has more power, the robot turns left. Likewise, if the left has more power, the robot turns right. This system is used in over 90% of the combat robots that have previously competed. This is the optimal design for beginners to use, as it is both easier to build and easier to design.

The other system is referred to as "car-steer" systems, where you have one (larger) motor driving the drive wheels, and a seperate (smaller) motor that steers the steering wheel(s), which may or may not be seperate from the drive wheels. If the wheels are the same, a differential must be used; if the steering wheels are not the drive wheels (think rear-wheel drive vehicles), a differential may be used for optimum drive characteristics.

Once you have your propulsion type determined, you then need to engineer your drive train. This is the part of the robot that actually moves the wheels/tracks/legs. Considerable effort needs to be applied to this part, as a weak/inadequate drive train is one of the leading causes for losing a match.

There are two output components to the design of the drive train: force and speed. Force in this context is the amount of pushing power that you have. Remember: Your robot not only has to be able to propel itself, it must be able to push an opponent with more force than your opponent is pushing you. A large percentage of Robot Combat matches are decided by the robot with the most pushing power. Likewise, your robot must have adequate speed to outmanuever an opponent, as well as enough speed for ramming damage (if that is your main weapon). Your pushing power can be determined by your weight class (assume that you need to be able to push two to three times your weight class), while speed should be estimated based on the amount of manueverability desired. Note, however, that these are contradictory components: designing a drive train for optimum force will result in lower speed, and likewise designing for high speed with result in lower pushing power. The only way to increase both is to use a stronger motor, which results in higher weight and cost. Obviously, this is one of the many engineering tradeoffs you must decide on.

In order to compute your pushing force and speed, you need to know two components of your motors: rotational speed (measured in RPM) and torque. (Remember, we're assuming your robot uses wheeled movement with a "tank-steer" system.) When you know what your motors can provide, and you know what your desired speed is, you can compute what reduction your drive train needs to provide.

Once you have the reduction determined, use the Drive Train Calculator to determine speed, output torque, and acceleration. You will probably use multiple iterations when using the calculator to determine the best motor specifications, wheel size, and reduction. Watch out, though! This calculator cannot tell you how much your "ultimate" drive train will weigh or cost!

Once you've decided on your drive train, you then must decide on your system to control your robot's movement. Thankfully, there are few alternatives for this, especially if you will be using a standard RC link for control. Electric motor controllers were made specifically for this, and are quite simple to use.

How will the robot damage other robots?

Much like the chassis design, here is where your creativity can really shine. When designing your weapon system, remember that you don't have to damage your opponent to win favor with the audience, you only have to appear to damage your opponent, although real damage goes a long way.

Many different weapon systems have been used throughout Robot Combat history, some not very effectly. Below follows a list of the basic types of weaponry used.

Also, you must decide on how you're going to control your robot's weapons. For those weapons that are simply driven by electric motors, electric speed control systems are perfect fits.

Once you've decided on your robot's mode of attack, you must then design the most effective way of delivering. We find that looking at past robots and events helps in deciding what works, and what doesn't. But remember, just because something didn't work before, doesn't mean it won't work now, provided that there are the right improvements. When dealing with weapons, effectivity is the key.

How will the robot survive other robots' attacks?

Dishing out the damage to your opponent is only one half of the Robot Combat. The other half is having your opponent dish out damage to your robot. You can prepare for survival by determining what kinds of damage your robot will most likely face. A good way to do this is to look at what effective weapons have been used in your weight class previously (see, you DO need to determine your weight class first). This will not only give you a good idea of possible returning robots, but what other builders might be building as well, as good results in Robot Combat tend to get copied by other teams.

Also, don't ignore the damage types listed above. Note which ones your preliminary design will be most vulnerable to, and determine a solution. For example, to defend against flipping, your robot either needs to be able to right itself, or it needs to be able to move upside down. As for the cutting and piercing weapons, adequate armor with substantial underlying structure will help keep your robot in the running.

Once again, effectivity is the key. Don't go too overboard on armor and defenses, as it takes away valuable weight from your drivetrain and your own weapon systems.

How will the robot get its power?

This not only includes power to drive your robot, but also power to drive your weaponry. There have been four kinds of power sources successfully used on combat robots:

  1. Battery Power - Simplest and easiest to implement for electric-drive robots. If you are building your first robot, stick with battery power. Here, the consensus runs with either Nickel Cadmium (NiCad) cells, or Sealed Lead Acid (Gel-cell) batteries. Both are approved for Robot Combat, and have been used extensively.

  2. Internal Combustion Power - Small gasoline-powered engines. Quite a few teams are moving to gasoline engines for their power source, and while this can provide decent amounts of power, this is not for the beginner.

  3. Pneumatic Power - Air-powered cylinders. Several robots use pneumatics to power their weapon systems, most notably "flipper"-type systems. Pneumatic power uses compressed air, which either needs to be stored on board or use a pump to generate the required pressure and flow rate. By activating cylinders, a pneumatic system can easily produce linear motion. To our knowledge, pneumatic power has not been used to move the robot itself. Pneumatic systems are not for the beginner to use.

  4. Hydraulic Power - Fluid (non-air)-powered cylinders. Hydraulics are similar to pneumatic systems, except that instead of compressable air, it uses uncompressable fluid, most often oil. As such, hydraulic systems require a pump to generate the required pressure and flow rate, which is an additional system. Hydraulic systems are quite complex, difficult to build effectively, and costly, and as such are not for novices.

When considering the power source, the two main components to design around are the weight of the system, as well as the size of the system. Gasoline engines and hydraulic systems are not small, and as such are not light, either.

One good thing about gasoline engines, hydraulic systems (which often use gasoline engines to power the pump), and pneumatic systems are the "recharge" rate. For gasoline engines, all you must do is refuel the tank (and if necessary, the oil reservoir); for pneumatic systems with a pressurized container, all you must do is refill the canister. For battery powered systems, you must either swap out the batteries, or charge the batteries. Swapping the batteries is quick time-wise, yet requires a second (or third) set of batteries. Charging batteries in-system requires a quick battery charger, and even then, can take on the order of hours to complete.

What will the name be?

There are many different sides to picking a robot name. Some believe that the name of a robot should strike fear into opponents, and seem "dangerous" to spectators, such as Carnivore, Nightmare, and Wedge of Doom. Other believe that you should choose a humorous name, such as Stuffy, Tentoumushi, and Knome. Others prefer generational names, such as Spike, Spike II, and Spike III, or "strong" names, such as Hercules, Agamemnon, and Slugger. What ever you choose as your robot's name, make sure it fits you and your robot.

Dan Danknick, of Team Delta, chooses a name first, before designing. Looking at Dan's track record, it might not be a bad system.... (For the interested, his next step is to have T-shirts designed. If you go this way, make sure to budget them in, as custom T-shirts, hats, etc. aren't inexpensive)


It happens to the best. No first design is final; the best that can happen is for your design to be the basis of the improved design. Be prepared for the possibility of several design/redesign iterations. It is best for your redesign to occur before you've started building, to minimize lost time (and wasted money). Here is where ample design time helps greatly.

Do not get deluded into believing that even your final design is final, as even after extensive design process, matters such as machining, parts acquisition, etc. can disrupt/change your design. Make sure that there are alternative design possibilities among each step. For example, if your design hinged around a specific motor, yet that motor will not be available, it would greatly benefit you if an alternative motor could be used with minimal redesign. While it is not possible to account for every possibility, remember that flexibility is a key component of the design process.

Answering these questions will help you design your key components of your robot that we discussed in the Starting out section:
  1. Chassis
  2. Movement
  3. Power
  4. Control Systems
  5. Weaponry

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