Battle Robot Building Tips
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Do your research
Basic plan and body design
Assemble a team and a workshop
Build a frame
Select your armor
Consider your mode of locomotion and turning
Steering control options
Motors, engines, and drive trains
Building your weapon(s)
While this was written many years ago with Battlebots in mind, the information still applies to robot building. All links mentioned below were last verified May 2012. If you want to relive some of the many great Battlebot moments, check out these videos.
Given the increasing popularity of robotic combat sports such as Comedy Central's BattleBots, a growing number of people are thinking about building a fighting robot of their own. If you are one of these individuals and you have no idea where to start then I highly recommend that you carefully read through this tips section. My background is in chemistry and computer science but I've recently been gathering a lot of information on building fighting machines and I'd like to share what I have learned with you. Many additional links can also be found in this text.
The first thing that I would like to make clear is that building a BattleBot of competitive quality is not easy. It takes a lot of hard work, both physical and mental. I should also mention that you will need to be prepared to spend a significant amount of money. Even lightweight competitors usually spend over a thousand dollars on construction and some super-heavyweights can cost tens of thousands to build. I'll try to present some money saving ideas to help in this respect. With that said, if you are willing to spend the time and the money, then just about anyone can build his or her own fighting machine. Keep safety in mind as well and be sure to have proper adult supervision if you are under eighteen.
There is a lot of information out there on the web if you are willing to look for it. I hope that this resource is a helpful start, but by no means should you rely on a single source for all of your construction advice. Visit our links section for just a small taste of what you can find on the web. Construction tips from experienced competitors are especially helpful. Spending a few hours on research can save you weeks of construction time and thousands of dollars. Try http://www.puppetmaster-robotics.com/faq.html for a good FAQ's page. It also helps to be familiar with the rules of whatever event you are planning to attend. Unfortunately, the rules and weight classes vary significantly from one competition to another, thus building a single bot for multiple competitions can be troublesome.
Watching the competitions is another valuable source of ideas. You can see first hand which general design principles are successful and which ones fail. My students and I often videotape and replay the televised matches. Don't get me wrong, no one likes a copycat and there is no fun in just copying someone else's design; but you don't have to reinvent the wheel either. Take a few ideas here and there and add some of your own original concepts to produce a quality bot that you can call your own.
So now that you have decided that you're ready to build a killer robot, you have to be sure you have the tools and manpower that you'll need. Very few builders work alone because of the huge number of man-hours involved. It is favorable to have someone with metalworking skills and someone with a background in electronics on the team. Most people that wake up one morning and decide they want to compete in Battlebots tend to be tinkerers of one sort or another. So chances are you have a workshop of some kind already if you are reading this article. But if you don't I suggest you have the following at your disposal: a big open area where you can make a real mess without getting in trouble, table saw, chop saw, rotozip, jig saw, hacksaw, drill press, hand drill, ratchets, screwdrivers, hammers, rivet gun, quick clamps, vice, vice grips, T-square, tape measure, grinder, sander, welder of some type, and finally a shop vac to clean up that really big mess you just made.
Before you start to build or order any parts, come up with a list of some key features that you want your robot to have. This is usually a system of give and take. Perhaps you want a bot with really thick heavy armor, or maybe that weight is better spent on larger motors to give your bot a speed advantage. Weight is a constant concern and you'll probably find it challenging to stay within the limits of whatever weight class you decide to compete in. Keep in mind that as your bot goes up in weight, the construction costs will dramatically increase as well.
Once you know your weight class and the special features you want your robot to have, you need to decide on a general body design. These include, but are not limited to, boxes, wedges, spin bots, and walkers. Naturally, more complex designs are fair game too, however, highly complex shapes result in large surface areas relative to their volume. Thus a dodecahedron bot design will cost you a lot of armor weight.
Various derivations of the basic box-like design are very common because it drastically simplifies the engineering process. Properly designed wedge bots have been quite successful in the past as well, however this design is getting rather old. Spin bots are an interesting concept that uses the external spinning shell of the bot as both the armor and the weapon. Team Blendo has an excellent site explaining the primary advantages and disadvantages of spin bots at http://www.m5industries.com. Walkers are bots that use some means of locomotion other than wheels. They have not been very successful because they tend to be slow and cumbersome. Realizing this inherent disadvantage, many competitions give walkers significant weight handicaps.
No matter what body type you decide to go with, try to keep your center of gravity as low as possible. Tipping over and being incapacitated can be your worst nightmare. If you really want to play it safe, design your robot to be invertible. The ability to drive even after being flipped was one of our team's key concept points. This does limit your weapons options, but we thought it was a worthwhile sacrifice. Keep in mind that there are a growing number of robots such as Toro that are exclusively designed to flip their opponents. A flippable design renders this attack almost useless as long as you have a sturdy construction that can handle the shock forces involved. Keeping your ground clearance as low as possible also helps to prevent flip bots and those pesky wedges from getting under you. I suggest having about half an inch of clearance.
My final piece of advice is to try to keep your design plans flexible and open to new ideas. Bounce your ideas off some friends. It's easy to fall in love with your own creation and we all know that love is blind. An impartial friend may be able to point out some obvious vulnerabilities that you overlooked. Leaving a little open space inside your robot can help a great deal towards making modifications. I would advise against designing the entire robot around a single weapon. Build a sturdy, reliable weapons delivery platform, and consider a modular weapons section. This way you can compete in different competitions or even different weight classes with your latest and greatest attack strategy without having to design and build an entirely new bot from scratch.
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A solid frame is the key to holding everything in place. Imagine the forces involved when a pair of three hundred pound robots collide head on at twenty miles per hour. Some builders simply attach everything to a bottom platform and place an armor shell around it. This is a mistake in my opinion, as a well-designed frame can add a great deal of structural integrity at a very low cost in weight. Your main options are to use round or square tubes. Round tubes tend to be slightly stronger pound for pound than their square counterparts. The problem with round tubes is that they can be harder to work with, especially if you are going to be bolting things in place. We decided to go with square aluminum tubing for Logan. Some other options would include I-beams or angle beams.
When you are designing your frame, try to determine the most likely directions of the most significant forces that your robot is likely to sustain. Don't waste valuable weight on unnecessary support. Finally, consider welding your frame together rather than using bolts or rivets. Welds are almost always stronger. If you have no means of welding, consider contacting some local metal shops. You'll probably be able to find a welder willing to work with you on such a cool project. High school vocational schools may also be willing to help out. Kids love this stuff.
It doesn't take a genius to realize that these machines need to be designed to take a lot of abuse. Your armor is all that stands between your vital electronics and your opponent's weapon. First, try to determine what locations are most likely to be hit during combat. Many builders place extra armor on the front of their robots. The new and improved kill-saws in the BattleBots arena, which pop up from the ground, shouldn't be overlooked either. You'll also have to decide if you want to bolt your armor in place or weld it onto the frame. Welding it to the frame is definitely stronger, but this makes it much harder to repair damaged sections. If you are going to go with the welding approach, you need to make sure that the armor and frame are built from the same material. Dissimilar metals such as steel and aluminum cannot be welded together. Even different grades of the same material can make the welding process more difficult. There are an amazing number of materials to choose from to armor your robot. I won't cover the more exotic varieties, but some common options include wood, steel, aluminum, titanium, and Lexan. I'll break down some of their advantages and disadvantages.
There really isn't much to say about wood. Ummm… I think it comes from trees. It's probably the least expensive option and you may have more experience in working with this material. Given the quality of today's combat robots, I don't think that one could expect wooden armor to last very long. Perhaps a 2X4 could be placed here and there as extra protection because wood does offer good compression, which could act like a crumple-zone to absorb shock damage.
Steel will offer you the highest level of protection dollar for dollar. If money is tight, I suggest you go with steel. It is very strong and is easy to weld. You'll go through many blades, but cutting it is fairly simple as well. Just be sure to use a metal cutting blade, not a wood cutting blade. There is only one major disadvantage to using steel. It has a very high density. A square foot of quarter inch steel (1018 grade) weighs a whopping 10.33 pounds. So to armor just a small cubic foot with this armor would cost you 62 pounds! You have various grades of steel to choose from as well. You can obtain detailed technical specs on many types of metal alloys and other materials at http://www.matweb.com.
Aluminum is not quite as strong as steel but it is significantly lighter. It also tends to be more expensive and slightly harder to weld. Despite these disadvantages, the huge weight savings that it provides often make it the material of choice, especially in lower weight divisions. A square foot of quarter inch aluminum (6061-T6 grade) weighs 3.53 pounds. As a rough rule of thumb, a high-grade aluminum alloy is about one half the strength but only one third the weight of an equivalent piece of steel. An excellent source of custom-cut aluminum can be found at http://onlinemetals.com.
Titanium alloy armor has been gaining popularity amongst higher budget robots. It can be prohibitively expensive but it's much stronger than aluminum and much lighter than steel. Plus it just sounds cool to say that you have titanium armor. I have never worked with this material, but I have been told that it can be quite difficult to machine and weld. To help a bit with the cost, you can look for sources of scrap titanium pieces such as listed at http://www.metalworld.com/a/0166.html.
Lexan has also gained much notoriety in the robotic combat community. Lexan is a high-grade form of polycarbonate (PC) manufactured by GE. It's even much lighter than aluminum and is very resistant to penetration. As a fairly non-scientific explanation of its strength; we found that an overhead swing from a large pickax failed to penetrate a quarter inch thick piece. Its flexibility also gives it good shock absorbing characteristics and makes it almost impossible to dent. The two primary disadvantages of this material are its expense and the fact that it can be easily cut. If you are going up against a large bladed weapon, Lexan may not be the ideal choice. If you are going to use this material, do not use regular paint or other organic solvents on it. You may not see any damage done, but it will significantly weaken the material on a molecular level. Use water based paints and cleaners if you must. Colored Lexan is also available. You can purchase and get more information about PC at http://www.goodfellow.com/static/A/CT30.html.
There are three major types of locomotion to choose from: wheels, treads, and walkers. There have even been some more exotic attempts such as the snake-like BattleBot appropriately named Snake by Team Sinister. Walkers are relative novelties and I've already discussed their advantages and perhaps more significantly, their disadvantages above. Tank-style treads are an interesting option that can provide excellent traction if properly designed. I personally decided against the use of treads because there is always a danger that they can fall off during combat. Of course, they are also a little harder to build than their wheeled counterparts.
Some variation of the basic wheel design is by far the most popular choice of locomotion amongst robot builders. They provide excellent speed and maneuverability. Some people think that rubber tires are susceptible to being punctured and flattened. This is true if you use air filled tires, which you should never do. Flat-proof foam filled tires are available at (Sorry - Site is no longer around).
You may want to use 2, 4, or even 6 or more wheels to drive your bot. Lightweights make common use of two wheel drive systems to save weight. Additional stability can be gained by adding caster wheels. Four wheel drive is fairly typical and some builders try to gain a pushing advantage with six wheel drive. Never underestimate the advantage of being able to push your opponent around. This allows you to use arena hazards to your advantage and scores good aggression points with the judges.
You'll want some way to steer your robot around. A few builders use car like steering but this is complex to build and, in my opinion, is just asking for something to break during combat. The popular choice is tank-like steering, where the left and right tires or treads can go forward or backwards independently. This enables a robot to turn in place if one side goes forward while the other side is in reverse. Naturally, you'll need at least two drive motors to achieve this.
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Let's assume that you are going to use the popular tank-like style of steering. You still have to decide on your method of electronic steering control. At this point, I am primarily discussing this from the human operator's control options. Your decision of steering control options will dramatically affect your electronics, which will be discussed later in this article.
The simplest option would be a simple on-off switch for the left and right drives. This will save you a lot of money on electronics because this could be achieved with simple relay switches. This provides poor control and should not be considered unless you absolutely cannot afford the other options.
You'll probably want to have reversing capabilities, and the ability to control your exact speed and turning radius. The easiest way to achieve this is to have each drive connected to a single axis joystick. Thus full speed forwards would involve pushing both joysticks all the way up, One stick up and the other down would result in a spin, One joystick full up and the other partially up would result in a slow turn, etc. You'll need speed controllers to achieve this, which will be discussed in more detail below.
A slightly more elegant approach is single 2-axis joystick control. In this case, full speed ahead would be achieved by pushing the joystick completely up, half up would produce 50% forward speed, and pushing the joystick completely to the left would result in a spin by making the right drive go forwards and the left drive go backwards, etc. Accomplishing this requires channel mixing which can be achieved by higher-end speed controllers, some radio transmitters, or in some cases via 3rd party electronic add-ons. Some drivers feel that single joystick control is more responsive, but I happen to prefer the 2 stick control myself. I guess it's a matter of personal preference. Just be sure you have good control of your robot. Good drivers always have the advantage.
Most builders use electric motors to power their bots. However, engines can be an interesting option to give you a power advantage over your competitors. Not all competitions allow the use of combustion engines but BattleBots does. I decided not to use an engine for Logan because they have a lot of restrictions such as how much fuel you can use. I also wanted Logan to run upside down, and to the best of my knowledge, an engine will stall when upside down as soon as the carburetor runs out of fuel. If you decide to use an engine, keep in mind that you'll have to have a means of remotely controlling the starter, the kill switch, and the throttle. This is usually done with servomotors. You'll also need a transmission and a means of reversing. This can get fairly complicated, but think of all the weight you can save on batteries! There is also the added advantage of not having to replace or recharge batteries between battles. Also note that the spark plugs in an engine can cause radio interference. Using resistor spark plugs can prevent this problem. You can buy small engines just about anywhere. I recommend the use of 2 stroke engines.
You'll probably end up using motors like I did because they are so much easier to use. Try to find motors that have high torque to weight ratios. The torque of a motor is usually measured in inch pounds. A motor with 50 inch pounds of stall torque would be the equivalent of 50 pounds of force applied to a one inch lever arm, or equivalently, a 5 pound force applied to a 10 inch lever arm. When a motor first starts up it produces a torque close to its stall value. This should not be confused with its continuous torque rating which is the amount of torque it is designed to produce for an extended period of time without overheating or smoking.
If you are using a raw motor (without a gearbox) you'll have very high rpm's but very little torque so you'll need to gear it down. You can use a gearbox, or chains and sprockets, or belts and pulleys to accomplish this. As an example, a motor producing 6 inch pounds of torque at 2000 rpm's could be set up with a 10:1 gear reduction to produce 200 rpm's at 60 inch pounds of torque (less a small amount due to gear friction and the like). So its slower but has more pushing power. This is the same idea you use when riding a bike; you would never try to climb a steep hill in tenth gear. The new 200 rpm's is a more reasonable speed for our tires to spin. You can get the speed of your bot in miles per hour by using the following formula: Wheel diameter in inches times rpm's of tire times 0.002973. This would give us 5.9 mph for a 10 inch diameter tire spinning at 200 rpm's. You can avoid all the worries of building a correctly geared drive system if you buy motors with a gear box already set to the desired rpm's. This way, you can attach the wheels directly to the shaft of the motor. Gearboxes are also nicely contained and less susceptible to damage or slippage.
You may want to try over-volting your motors. Let's say you have a 12-volt motor that is rated to produce 0.5 horsepower at 100 rpm's drawing 10 amps of power. If you take this motor and hook it up to a 24-volt source, it will produce 2.0 horsepower at 200 rpm's with a 20-amp draw. Notice that when the voltage was doubled, the rpm's and the amps also double but the horsepower was quadrupled. There is of course a price to pay, you may overheat and burn out the motor. However, robot combat bouts are usually only a few minutes long and thus motor overheating is less of a problem. You may also try adding heat sinks or cooling fans to counter this. Don't overdue it either. I wouldn't try running a 12-volt motor on a 48-volt system. Logan uses 24-volt motors running on a 36-volt system. Higher voltage systems are also more efficient as less energy will be lost to the heating of wires. But remember, to achieve this higher voltage, you'll need more batteries… and batteries are heavy!
Motors can be an expensive part of the robot and you'll probably want a spare as well, in case one burns out. One inexpensive option is to use automotive 12-volt power window motors. These are generally not suitable for heavyweights unless you're going to use some sort of exotic 12 wheel drive system or something. You may find the power and high rpm's of car starter motors attractive, but be careful… most starter motors are not reversible. They are also exceedingly heavy. If the junkyard is not your style and you'd rather just shell out the cash you can find a wide variety of motor suppliers online. You might also want to check out http://www.3rivers.net/~cmac/cmac16.htm.
Unless you went with the option to use a combustion engine, you'll need to get some good quality rechargeable batteries to power your motors. Unfortunately, batteries are very heavy and can cost you a lot of weight. Don't try to use car batteries. For one thing, they are not allowed in most competitions because they'll leak acid when upside down. But you wouldn't want to use them anyway because they are designed to produce very high amps for a short period of time. You'll want batteries designed to produce a moderate amperage for a sustained interval. Most builders choose to use sealed lead-acid batteries or nickel-cadmium batteries. They'll both do the trick but nickel-cadmium batteries are a little more efficient but much more expensive as well. Also remember that you can hook up several batteries in series (positive to negative) to obtain additive voltages. Logan uses three 12-volt batteries to obtain a 36-volt system. When you place batteries in series, they should all be the same voltage. For example, if you wanted an 18-volt system, you would use three 6-volt batteries, not a 12-volt and a 6-volt. This is because the battery of lower voltage would be forced to work harder.
The most important thing to keep in mind when selecting your batteries is the amount of power you can draw from them. The total energy that a battery can supply is measured in amp hours (AH). You may think that an 18AH battery can produce a current of 18 amps for an hour, but this is not the case! You see, the slower you draw current from the battery, the more efficient it will be and the battery companies sort of cheat a little with their rating systems. The way that 18AH rating was achieved was like this: 0.9 amps was sustained for 20 hours and 0.9 X 20 gives you 18AH. However, as you draw current faster, more energy is lost due to the internal resistance of the battery. This same battery can only supply a current of 12 amps for an hour. You may have powerful motors drawing over a hundred amps and thus the efficiency of your batteries drops even further. So as a general rule of thumb, I suggest that you divide the AH labeled on the battery by 2 in order to provide a more realistic figure. It is also very important that you realize wiring batteries in series increases the voltage but does not increase the AH rating. You can wire batteries in series for additive voltage, or in parallel for additive AH but you can't have it both ways.
To complicate matters even further, you basically need to make an educated guess as to how much current your motors will be drawing. The most they can draw is based on the stall amperage of the motor. The least you can expect them to draw is their nominal continuous amperage. (You'll have to ask the manufacturer of the motor for these stats if it is not printed on the motor.) The actual amount of amps that the motors will draw is dependent on the load placed upon them. Thus a motor draws more amps when the bot is accelerating or pushing an opponent. My best advice is to take an average of the nominal and stall amperages of the motors to try to get an estimate. Naturally, if you used over-volting as mentioned above, you'll have to take this into account as well. If worse comes to worse, you may have to use a little trial and error or simply buy batteries that you know will provide much more power than you will need, but this again costs valuable weight. Once you're ready to buy your batteries, you may want to check out Powersonic at http://www.power-sonic.com. They have a good selection to choose from.
If you're going to buy high quality rechargeable batteries, you should get a high quality charger as well. Some cheaper chargers actually dump some AC current into the battery along with the DC. This will shorten the life of your batteries, and cost you more money in the end. If you are in doubt as to which charger to buy, simply ask the manufacturer of the battery you select to suggest one.
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Speed controllers are electronic components that do as their name implies, they control the speed of your motors. But a good quality modern speed controller performs many other functions as well. If a motor is put in reverse, the controller will be sure to stop the motor before reversing. This prevents damage to the motor. The controller can also put much of the energy of the spinning motor back to the batteries in a controlled fashion when braking. Remember, a spinning motor is also a generator. Some allow you to set various types of acceleration and deceleration curves so you can tweak the responsiveness of your bot. Failsafe mechanisms for short circuits and overheating may also be included. Speed controllers are complex pieces of electronics and come with an accordingly steep price tag. They are usually the most expensive part in a robot.
Speed controllers are usually rated according to amperage. The more amperage that they are rated to handle, the more they cost. They can cost up to $800 and depending on your method of control and steering, you may require two such controllers (for left and right drive) or perhaps even a third to control a weapon motor. If you use speed controllers with higher amp ratings than you require, no harm will be done other than to your wallet. Getting controllers that cannot handle the amps of your motors will result in controller shut down or even permanent damage if it is not equipped with some sort of temperature monitoring system. The amp rating of a speed controller is usually the amperage that it can sustain for about a minute or so without overheating. Again, you can add heat sinks or cooling fans to try to get longer sustained amperage from a controller. But either way, be sure the controller can handle at least three times the amperage of the nominal draw of your motors.
Some advanced controllers such as those offered by Vantec at http://www.vantec.com can plug directly into your radio receiver just like a servomotor. This can simplify your electronics. Vantec controllers can also perform channel mixing to allow a single 2-axis joystick to give you tank-like driving.
If you require high amp, high voltage (36 volts and up) supply, you want to consider using 4QD controllers, which can be found at http://www.4qd.co.uk/index.html. They are less expensive for a given amp rating but don't allow you to plug directly into your radio receiver. You can handle this in one of two ways. You can use standard servomotors to control a joystick-like potentiometer, which is in tern connected to the controller. This may be a bit cumbersome to set up but has the advantage of electronically isolating your controller from the receiver. Or you can use a 3rd party electronics adaptor to allow a 4QD controller to interface with the receiver such as the one found at http://www.teamdelta.com/products/prod2a.htm. This product will not allow for dual-channel mixing so you'll have to make further modifications if you wanted single joystick control.
You don't want to spend hundreds of hours building a robot only to lose a match because you lost radio contact with your machine. You may be tempted to use an inexpensive AM radio transmitter but these are very susceptible to interference. The last thing you want is an out of control BattleBot on your hands. Use a high quality FM transmitter, or better still, a PCM transmitter. It is also a good idea to keep your receiver antenna at least one inch away from metal surfaces. The biggest decision to make is how many channels you will need. You'll need at least two, one for each drive wheel. You then need channels for weapons and the like. A good 4-channel FM radio will cost you about $200. Some builders use a pair of 2-channel radios instead. This allows one person to drive the bot, while the other controls the weapon. This later option is probably what we will use to control Logan. You can find a good selection of radio controllers at http://www.towerhobbies.com.
This is probably the most exciting and fun aspect of building a combat robot. Just let your imagination run wild. Well, actually read over the rules of the tournament before you get too crazy. The chemist in me developed a plan to use a hollow spike to inject a liter of concentrated nitric acid into the opposing bot. Unfortunately for me, most tournaments don't allow for the use of liquid weapons. I was going to call him Venom.
Be creative but be sure your weapon is reliable and capable of inflicting real damage. There are many weapons out there that lack the ability to damage a well-armored robot. If you have a little weight left over at the end of construction, you may want a backup weapon as well to help give your robot the edge it needs to win. A modular weapons design would also be useful to keep your opponents guessing as you experiment with various blades and so forth.
I'll try to briefly discuss some of the advantages and disadvantages of the major weapon varieties. Saws are a fairly common choice, but they actually do very little damage. Your opponent is not going to stay still for you, so keep that in mind. Blades can also be easily damaged, especially by a side impact. The few effective saws that I have seen have been gas powered for more kick and mounted horizontally to avoid the problem of side impact damage.
Spinning disc weapons are sometimes confused with saw blades but they really work on a much different principle. A disc builds up a lot of kinetic energy and delivers all of its impact to the opponent in one fast blow. This energy is usually obtained via a combination of high rpm's and a large diameter, which together generate very fast speeds on the outer perimeter. They don't have a lot of sharp teeth for cutting, rather just a few teeth for ripping. This also imparts a great deal of shock damage to the electronics of the opponent. But for every action there is a reaction, so you had better have a sturdy system to absorb or allow for shock on your bot as well. Once it hits, the disc usually loses most of its momentum so it may take some time to rev up to speed again. Much like the blades, they can often be easily damaged as well. Long rotating cylinder drums can be used much like a disc, but they build up momentum using a larger mass with a much shorter radius. This can be more durable but I haven't seen one with the same knockout power as a well-designed disc.
Spikes are also common. Fixed position spikes make a great and very simple secondary weapon, allowing you to at least do something if your primary weapon breaks, but they rarely penetrate a well-armored bot. If they are too long they can become awkward as well. For a spike to do real damage, it needs to be able to retract and eject with a great deal of speed. This is usually accomplished with pneumatics. From what I've seen, they often fail to work properly and if used frequently, the expanding air cools the cylinder so much that later strikes have less force. (The volume of an ideal gas is directly proportional to temperature.) An ejection mechanism can also be achieved using a winch and some large springs to store the energy. I feel a design of this type has a lot of potential and we plan to build such a weapon for a future BattleBot that we will name Bond. Logan was actually going to get a spring loaded spike with 2,600 pounds of ejecting force, but it just got too expensive for a first-time construction attempt.
Flipping arms have increased in popularity. Some bots can be incapacitated when flipped upside down. But because no one wants to lose like that, many builders are using invertible designs such as Logan's. This renders an attack of this sort almost useless, except for the shock impact. Pneumatics or linear actuators are usually used to power flipping devices.
Swinging overhead pickaxes and hammers are found on many bots. They can strike on the top of a robot, where the armor is often lighter. It can be hard to hit a moving opponent with such a weapon though. They usually require many hits to be effective as well. Large blades have also been used, but I really never see them do much damage. Pickaxes can also be placed on the side of a bot and spun into the opponent with great force. The big problem with this is that the robot has no maneuverability when it's in this spinning offensive mode.
Clamp bots are very interesting. They are complex to build, but allow a bot to grab onto and control the opponent and perhaps lift it off the ground as well. Clamp bots can then better use arena hazards to their advantage. I like this concept a lot, but getting hold of the opponent when they are moving around and attacking you is probably harder than it sounds. I suppose the same sort of thing could be used for a crushing attack, but this would require a lot of power.
The final weapon type that I will discuss is the drill. Drills can do quite a bit of damage but they probably take too long to be effective under most circumstances. Perhaps a drill could be combined with a clamp bot to hold the opponent in place while the drill does its thing. Then again, this is probably a little too complex to be practical. Just a thought.
There is at least one other potential power source besides electric motors and internal combustion engines worth mentioning. The use of pressurized air can provide a bot with fast and powerful weapons. However, such systems can be very dangerous to work with if you are inexperienced. I've also seen some pneumatically powered weapons with reliability problems but it also works well for some bots. You can often achieve the same type of movement using an electric linear actuator, but it will be slower. For example, the lifting arm of Biohazard is powered by two powerful linear actuators. I really don't know much about this subject so I'll leave it at that. Perhaps in the future I'll want to build a pneumatic weapon and I'll learn more about the topic. You can check out http://www.hydraulics.com if you're interested.
You'll be surprised at the number of strange odds and ends you'll need to find to construct your BattleBot, especially if you're building a complex weapon. The best way to find such parts is online. I suggest trying Efunda, which has a huge engineering database of parts and suppliers. Let's say you are looking for a helical compression spring that is 10 inches long, 2 inches wide, and compresses to 6 inches. Good luck finding this right? Actually, it is easy. Just go to Efunda. Click on "springs" under mechanical components. Next click on helical compression springs. An entry form will now appear that lets you fill in various parameters with maximum and minimum values. Enter 2 for the max and min outer diameter, 10 for max and min free length, and 6 for max and min solid height. Now click find at the bottom and presto… one exact match and five close matches are found. The part numbers and names of the companies complete with online listings are made available.
Sometimes, even this huge database doesn't have what you want. You'll then have to make it yourself or have someone else custom make the part for you. This can be quite expensive, so try to keep the custom parts you need at a minimum. Consider altering your design slightly to allow for the use of a stock part. You can find companies that will make parts to your specifications online such as at (Sorry - Site is no longer around). This same company also builds titanium bike frames. These are light weight and strong and could be easily modified for use on a combat robot. Their bike page can be found at http://www.spicercycles.com.
Getting sponsors can be hard to say the least. You'll probably have to ask a hundred companies to get a single response. You can improve your chances if you have something to show them besides a drawing. Try to get your robot construction started before you contact them. This way they know you are serious. A web page couldn't hurt either. Be sure to explain that sponsoring can be a great way to get inexpensive advertising.
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