Battlebots Alumni
Knowledge From Experience
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Welcome
This web site was made by Alumni of the Battlebots program at Olathe Northwest High School. It is designed to pass on to future classes the the knowledge that has been gained from experience in Battlebots competitions. This is crucial because unlike other schools, our program can not be participated in for all four years of high school.
This is Derek Joseph and I am the one who started this web site. I was on Team EOM and designed the the flipper weapon of Spatha. Some of you may ask why I would build this web site. I mean after all, I already graduated and I wasn't even in the class in the first place (I joined after school started and worked each day before I went to my Internship). The reason is that I think our battlebots should be doing better than we have done in the past. I am not happy with our Aerospace & Engineering Program only getting 13th out of 44 teams, we need to strive to become the champions. Last year we did extremely better than the year before, and hopefully, with some help, your team can do the same. Use this web site as a resource during your research and review it often because there are many things which need to be remembered during testing and before the competition. Navigation
Design Process
Four Wheel Drive
Take a look at some of the 240lb. or 320lb. battlebots. Quite a few have decided to use six wheels to drive their robot. That is because they want to have as much traction as possible to push the other battlebot. Even Ziggy, the 320lb. flipper we modeled ours off of has six-wheel drive. The reason why fewer teams do this at 120lb. is because of weight. This does not mean that you should resort to two wheels, though, because a four wheel drive system can be done without sacrificing much weight.
Double RepetitivenessWhenever possible, back up each component that might malfunction with a duplicate. The probability of one component failing is high, but the probability of a component and its duplicate failing simultaneously is very low. This is why four-wheeled-drive is a good idea because you have two wheels for each side. Each wheel should have its own chain because if it shares the same chain and it breaks, then you are immobile and loose the match. If you have two, one can break and you will still be able to function properly. Most importantly, double repetitiveness should be applied to the electrical system. What are you going to do if one battery gets grounded or if a speed controller get fried? If you have two performing the same function, one of them is still going to work. Gyroscopic EffectMany builders of any kind of spinner robot do not realize or completely ignore the gyroscopic effect on their robot. Their excuse may be that their weapon not going fast enough to affect their battlebot, but think of it this way, when you go 5 mph on a bicycle, the gyroscopic effect is what's keeping you from tipping over. I'm not going to explain what it is, you have to look it up yourself, but no matter what, it greatly affects any spinner weapon. Just watch some videos of Copperhead, when they turn too fast, their bot completely flips over. To fix this, you need to have a wide enough base and a low center of gravity to support the tipping force on your robot when you turn. For any kind of robot you need to remember Newton's third law that states that for every action (force) there is an equal and opposite reaction. So when a flipper weapon actuates, its going to shove the front of the battlebot into the floor, and when a spinner spins up, its going to twist your battlebot the opposite direction. The design of the battlebot needs to minimize these unwanted effects in order to improve the effectiveness of the weapon. Anatomy of a Wedge
MaterialsIt is very important to do some research on what types of material you need. Important factors to keep in mind are tensile strength, weight, weldability, and workability. While Titanium is very strong, it has poor weldability and workability so it would not be a good material for some applications. Steel is very common but it is often unnecessary. The only place with a need for heat-treated steel is on the blades of spinning weapons. The frame should be made out of aluminum because it can be just as strong as steel and be lighter in weight. Using something such as 6061 would be a good idea for the frame because it can easily be welded together. Try making the frame out of sheets of 6061 aluminum that are about 3/8" thick and get a waterjet to cut out holes for mounting components and to lighten the frame. These vertical plates can then be welded together to braces that run the width of the robot to separate the plates. 7075 is what Spatha used for the weapon and it came out of the competition without a scratch. This aluminum alloy has double the tensile strength of 6061 and weighs about the same. The only downside is its higher price and that it can only be welded using a TIG welder. This still makes it an excellent candidate for a weapon such as a flipper, but not so easy to incorporate into the frame. In case you were thinking of mixing some different alloys in the frame, this can not be done because only identical alloys can be welded together. I am surprised how many robots did not use polycarbonate (Lexan) for their armor. I think it would make sense to use this since after all, it is bullet-proof glass. Our 1/4" Lexan worked very well because it never got bent and was able to absorb the 18 hammer hits we sustained in our first match. The couple of other robots that used Lexan got ripped to shreds because their armor was only 1/8" thick and was poorly fastened to the frame. With good fasteners and 1/4" lexan you should be able to handle any kind of enemy, it might crack under stress, but it will not get bent or punctured. 3d Design
Axles
SafetyBefore you start building you must understand all of the safety rules and have a solution for EACH requirement. You need to know the rules so well that you need to have the memorized. When you are talking to corporate sponsors, if they are going to get you the parts you need you will need to know the specifications off the top of your head of what will work and likewise, what will not meet the requirements. I assume that you will have some kind of moving weapon, so there needs to be a safety restraint to stop it from moving. If you power up the robot, the restraint needs to be able to stop the weapon when it is activated, preferably without breaking or bending something on your bot. You need to be able to power-up the robot with the restraints on, stand away, and then take them off without touching the robot or placing anything in the path of the weapon. For spinning weapons, put the restraint as far away from the point of rotation as possible because this is where there is less shear force. For flippers, slip a long rod through the side of the front wedge of your robot so it goes through holes towards the tip of the weapon. Since this is the area that travels the farthest, this is where the least amount of force is at. AggressionNo matter how good your weapon is, you are not going to win without a descent drive system that not only dependable, but can also be easily controlled. It is going to look very bad if you go in zigzags all over the arena when you are trying to attack your opponent. If you chase your opponent around in circles, the judges will not be able to figure out who is chasing who. To identify yourself as an aggressive battlebot, you need to be able to chase down your opponent and react quickly when they turn away (with a good weapon, they will try to run away). Battery Current
Web AuthoringTo get sponsors, it is very important to have an attractive web site where they can see your design goals and your progress. A professional looking web site shows that you are a legitimate team and expect to do well in competition. It takes Google and other search engines about two months to add a new web site to its search results so the sooner you get something posted the better. Then you can go back and make updates as you finalize the design. I built last years web site with only one semester of web authoring experience. If nobody on your team can do this, you will need to get someone from E-Comm who is nice enough to do this for you. Whoever does it should get started right away so you can have it up while you are trying to get sponsors. And you can't just tell them to make a web site, you need to provide a word document of paragraphs of information for them to post as well as some pictures. Have them teach someone on your team how to edit and add information so you do not have to rely on them to make updates. RESEARCH
It is extremely important to do you research. Do not just settle on a component just because it is what you have and what you think will work. Find all the different possibilities and then make your decision on what to use. Maybe even get two different ones and test them out yourself to see which one will do the best (because of the budget this will not work with more expensive items though). There is a lot you can learn from other robots that are similar to your own and even ones that are completely different. If you do not know exactly what you want to do, you need to do a lot more research.
Wheels
Battle KitsJust because you want to make your own custom robot, do not overlook the Battle Kits. The best part about these kits is the compact and lightweight drive system. It is built inside a strip of 3" square extruded aluminum. They can easily be bolted to your frame and more weight can be taken out if needed by cutting out some more of the aluminum. You can either go with the modular drive units or a complete middleweight (120lb) battlebot. If you get the modular drive units you will need four units and four motors to have enough torque for the standard speed ratio which actually is pretty fast. The benefit of the complete battlebot is that the drive systems for each side are in the same 3" piece of aluminum. Just remove the base-plate and the rest of the frame and use the chain drive system. You can get away with only two S28-150's with this because it should have a higher speed reduction. Compared to Spatha, if you decide to use the four motor configuration, it will only be a couple of pounds heavier than our configuration. You might need some more batteries to power the extra motors but if you get Lithium-Ion, you will have enough weight to spare. The reason why you should buy from this manufacturer is that they have the holes for the axles precision drilled out to meet the amount of slack that the chains gain over time. Tight chains allow them to get rid of chain tensioners which you will need if you made your own. |
The Design process is very important because you don't want to spend the whole year building a robot that is difficult to assemble, requires custom components, and might not work. Keep in mind that wasted space means wasted weight. The smaller and more compact your robot, the less armor you are going to need. Trust me, the armor you are wanting to use is going to add up to a large percentage of your weight. A compact battlebot also makes it easier to have a strong frame which has few weaknesses. Do not take this advice to far, though, because having too small of a robot (less than 18"X18") means that you will end up with armor that is unnecessarily thick for a 120 lb. robot. Titanium Knight last year had a wedge made out of 1/2" Titanium. Yes, nothing is going through that but it is also extremely unnecessary. Spatha used 1/4" of lexan which held up just fine. You are at a higher risk of the armor getting bent or pealed off your robot than a weapon penetrating the armor. This means that the fasteners that are used are just as important as your armor.
If you want your robot to be fast yet maneuverable (which you should), you consequently need the width between the wheels to be very large (THIS ALSO APPLIES TO A ROBOT WITH TWO WHEELS). It will be very difficult to make precise turns if the width of the robot is small because it will turn very quickly. You want to be able to make precise turns so you need to slow down the speed the bot can turn. Space out the width (not the length) between the wheels so that the circle the wheels follow on the ground has a large circumference, thus slowing down the speed the bot can turn. For a four-wheel-drive system , it is also important to have a large width because it will make your bot more nimble. Think of it this way, does a Drag racecar have a good turing radius? Of coarse not, it too long and narrow, a larger width AND A SHORTER WHEELBASE(length) is going to turn easier and be more nimble.
Spatha's flipping weapon could get underneath any robot. The wedgebots that we faced were, ironically, unable to get under us, yet we could effectively use our weapon because we could get our weapon under them. The reason for this was because it was made of two wedge shaped points, six inches apart and 1/2" wide. By minimizing the surface area in contact with the ground, the easier it was to keep it in contact with the ground without getting stuck. The key is to minimize the width of the wedge and reduce the surface area touching the floor. The floor of the arena is anything but flat and level making a wedge as long as a bot useless. A long straight wedge, will not be able to keep in contact with the ground along the whole tip. Make a sophisticated weapon that does not require a wedge that is the length of the battlebot.
Doing the Solidworks for 3d modeling is very time consuming and it is best to be familiar with the program before you start designing the battlebot. This will minimize the amount of errors you will run into and make it easier to meet deadlines. The team members assigned this task will have a very big role in the structure, size and shape of the battlebot. I had to do the frame and armor myself to meet a deadline before I could get any sketches from the rest of the team. Since doing the solidworks is such a big task, the rest of the team needs to get involved. Everyone needs to do their research and figure out exactly what parts they want. The information given to the drafters should include the size, type, number, layout, and dimensions of all the parts. You will be lucky if your robot is within a tenth of an inch to your 3d model, so there is no need to have a dimension tolerance of .001 inches. Create a 3d model that is as in-depth and accurate as possible because this will help down the road when you are trying to assemble the battlebot. Find a place for each component and do not leave too much open space. A well designed virtual battlebot will prevent a lot of confusion later.
They only effective way to support axles is by placing a bearing and pillow block on both sides of the wheel. When you get hit with the hammer, any other configuration will break something or bend the axle. Certainly do not put the wheels directly on the end of the output shaft of a gearbox. That is not what they are meant for. Side loads on the output shaft cause misalignment of the gears resulting in failure. Instead use a similar configuration using a shaft coupler to connect the output shaft to an axle supported by two pillow blocks.
Do not over-volt Magmotors because they will be inefficient an end up drawing more current than you can provide. Instead, add more batteries in parallel to give the motor double the amps. Take a look at Mrs. Metcalf's 2007 team's interview with Blender. They have at least ten battery packs crammed in their robot to supply enough power to their weapon. For two Magmotors you are going to need about 9.6 amp-hours of current. This means at least 3 battery packs with 3200mAh cells. I suggest using the Lithium-Ion packs that you can purchase from 
Also, go and talk to professionals that might be able to solve your problem. Bill Morse from Flo-Products helped us out tremendously with the pneumatic system last year. You should also look through the notebooks from last year because they have really good information about how we designed our battlebots. All in all, good research builds a good battlebot. As an assignment, email Mrs. Metcalf (bmetcalfonw@olatheschools.com) or Mr. Manbeck (kmanbeckonw@olatheschools.com) your name and let them know that you have read through this web site. This is for points so do it right now before points start getting deducted. You can not mention this to other members of the team, but you can try to persuade other team members to read through this WHOLE web site (because of the good information, of course!). Thank you for doing this miniscule amount of research so far, and wish you the best of luck for all the late nights you will be spending on this.
Before they are used, all wheels have a thin slick coating around the outside of the tire. It is important to wear this out so you can get to the softer center of the tire that has better traction. For Spatha, we thought we had a revolutionizing idea to lathe the outside of the tires so they are flat instead of rounded, creating a large contact surface. It turns out that it is expected for robot builders to do this when purchasing new wheels. Bill Goodman can to this for you an give you a professional-looking finished tire. Some teams add solvents to their wheels to soften them up before a match and creating better traction. The only down side to this is that they wear quicker and need to be replaced. Nevertheless, you are going to need replacement wheels anyway. The Colson wheels that we used work decently and do not wear quickly but they are kind of hard. Some better wheels are part number 2829T58 and sold at