How to Design the Best 150 Gram Combat Robot

Materials

The entire list of required materials for your specific project will differ from this, but this will provide a baseline for what components to look for.

  • TPU 95A 3D Printer Filament
  • 3D Printer Filament
  • Laser Cut Steel(for weapon and forks)
  • Malenki Nano
  • 2-cell battery(between 200 and 300 mAh)
  • 2 x N-10 drive motors
  • Hub-mounted Weapon Motor
  • Single Channel AM32 ESC
  • EVA Foam
  • Liquid Latex

    • Weapon

    Figure 1

    Figure 2

    Arguably the most important part of a combat robot is the weapon: it's the only way to do damage to the opponent and provides the most points in the event of a judge's decision. The best of these weapon designs is a vertical disk spinner with a hollowed-out core and 5-10 mm of bite.

    The reason you want to have the disk hollowed out in the interior is to maximize the potential kinteic energy of every hit and thus the potential damage your robot can deal. This is a result of the formula for the kintetic energy of a spinning mass(see figure 1) and the formula for the moment of Inertia(MOI)(see figure 2). Because the radius is squared and the mass is simply to the power of one, that means that having a lighter mass at a farther distance will provide more energy than a heavy mass concentrated on the inside. This is why the shape of your spinner should be hollowed out(see figure 3). This is further supported by Team Just ‘Cuz Robotics' video Combat Robotics Basics: Spinner System Design, where he says that “kinetic energy is simply a factor of how much energy is stored in the blade as it is spinning, and that is determined … by a function of the shape of the weapon known as the moment of inertia, or MOI [and] the MOI of a weapon is basically the average position of mass away from the center” (Team Just 'Cuz Robotics 2024).

    The next step in designing your robot's weapon is defining what amount of bite you want on your weapon. The bite of the weapon is the maximum insertion that the tooth can reach into your opponents robot, usually just the tooth height but it can be less. To see a good example of what a good amount of bite looks like see at figure 3. THe calculation for the tooths bite it perfectly explained in Marco Antonio Meggiolaro’s paper Riobotz Combat Tutorial, where he explained that “both robots would approach each other by dmax = (vx1+vx2)⋅∆t = (vx1+vx2)⋅π/ωb. So, the tooth bite could reach values up to dmax” (Meggiolaro 2009). Given that the average robot will move at 2.5 mph with a weapon speed of 4000 RPM, we can calculate the the max insertion will be 13.4 millimeters, but because we are making a fairly small For a small robot, 13mm of bite is pretty unreasonable, so we find that a good value for a bite on a 150 is about 10mm with some wiggle room up or down of about 5mm.

    Figure 3

    Spin: RPM Bite: mm
    Teeth: #
    Speed: mph

    Armor

    Figure 4

    Next to the weapon, the armor of your robot is one of the most impoartant parts of a combat robot due to how the fights are scorred(With 5 points for damge, 3 for control, and 3 for agression). As a result of this scoring and the need for your robot to survuve if you want to win in a KO situation, the armor is one of the most important parts of the robot and the construciton of it is vital to having a winning chance. The best way to design this armor is to make it out of TPU with a curved exterior and, where its needed, closed cell infil for lighter but slightly less durable armor.

    TPU is the best choice for the material of the armor due to its supreme impact absorbance durablility, and layer bonding when compared to almost every other 3D printer filament. Combinging the relativly cheap of cost TPU with those atributes it is the obvious choice for your robots armor. This is shown by MatterHackers, a 3D printer filament company, when they describe how “TPU is a flexible, highly durable filament that's perfect for parts that need to bend or flex without breaking. This makes it an excellent choice for shock absorption components in combat robots or parts that need to withstand high stress. TPU is also resistant to abrasion, wear, and tear, adding to its longevity” (Matter Hackers 2023). Due to this durability TPU is able to survive the high stress scenarios of a fight. Adding a curved surface(see figure 4) to this is able to further increase it durability by providing a more rigid shape to reduce bending and thus stresses on the armor as well as providing a sloped surface for the opponents weapon to slip off of.

    The infill of the armor can also be extrememely important to both meeting the weight requirment as well as adding armor thickness where necassary(see figure 6). This infill can come in 3 different categories, open cell, closed cell, or other. Other is generally only used for very specific cicumstances, so when printing parts for your robot it is sualaly best to use either closed cell or open cell. Of the two remaining geometries, Sergio De La Rosa’s article Design of Flexible TPU-Based Lattice Structures for 3D Printing: A Comparative Analysis of Open-Cell Versus Closed-Cell Topologies excellently explains the “substantial differences in the manufacturability of the topologies, with open-cell structures exhibiting more pronounced defects. Additionally, the unit cell size and the resulting density of the samples were found to provide design advantages, as closed-cell topologies demonstrated superior load resistance” (De La Rosa 2025). Because of the superior strength of closed cell topologies, it is better to use such infills in the armor and other parts. A good infil pattern to accomplish this(and what your robot should be printed in) is cubic(see figure 5).

    With all that said though It is still wise to try to minimize the infil in the armor possible because it decreases the strength of that section of armor, which while it might be getting directly hit, it will be taking resulting forces from other sections getting hit. Thats all just to say, design your robot to minimze the amount of infill necasary in almost all cases.

    Figure 5

    Figure 6

    Forks

    Figure 7

    Figure 8

    Including forks onto your combat robot will allow you to greatly increase both your control over the match and the otehr robot as well al provide you with a better angle to be able to deal more damage to the opponents robot. Forks are able to lift your oponent further off of the ground and give your weapon a better chance at making good contact with teh oponent robot by exposing their underside for your weapon to hit. This allows the weight of the oponent robot to counteract the force of the weapon better and allow the weapon to dig deeper; thusly doing more damage.

    Using Forks that have a relativly low angle to the ground will provide the optimal geometry for your forks, this is ecelently explain in The Organic Chemistry Tutor’s video Introduction to Inclined Planes, where he shows that the formula for the acceleration of a block down an inclined plane is “g*sinθ,” with theta being the angle between the ground and the surface of the inclined plane. This means that the force required to push a mass up the inclined plane is at least m*g*sinθ. This means that for a given mass, 150 grams, it will get easier and easier to push them up the slope, fork, as the angle relative to the ground becomes lower. This ease of pushing means that you will have a better time getting the oponent onto your forks and thus getting good hits. A good fork geonemtry also includes having a pivot point to get the best chance of getting under your oponnent as possible(see figure 7).

    When adding forks to your robot you should also make sure to limit their movement because it can cause many unforseen problems if they are not. This is explained in Team Cryptid Robotics’ video 7 Things I Wish I Knew Before Building My First Robot, where they say that “if they can rotate too far downwards, that's a pretty good way to end up high-centering your robot, [and] … if they rotate upwards too much … [then] they are basically not doing anything” (Team Cryptid Robotics 2025). When you high-center your robot you more likely than not out of that round because it almsot fully prevents you from driving your robot in any controlled manner and will often lead to you getting counted out and eliminated for not moveing. When the forks go to high then they do nothing and become a waiste of weight. A good range of motion for your forks is about 30-45 degrees

    Limiting your forks might sound like a daunting task, but it simply entails adding a larger flat portion to the back of your fork and a flat or angled area to your mounting point on the frame(see figures 7 and 8). When limiting your forks, ensure that they will never be able to pass under the robot and will never pass the vertical plane in either direction, this will almost ensure that your forks will stay where they should. Lastly, consider the flexiblness of TPU in your design and add extra room for wiggling that will still keep the fork in their correct position.

    Electronics

    The electronics selection for your robot is extremely important to the functionality and overall performence of your robot. Without proper electronics selected, you can burn out a motor, esc, or even your receiver. Chossing the right electronics can be the difference between losing because your drive motors die or winning because they refuse to give up no matter the damage. A good electronics selection for your 150 gram would be a Malenki Nano, a 2-cell battery of between 200 and 300 mAh, and an AM32 weapon motor ESC.

    The Malenki Nano is the best choice for any 150 gram no matter the weapon or drive varity for one simple reason: it only weighs 2.6 grams according to ITGresa, an online parts retailer. When compared to other popular receivers, like the Flysky FS2A which also weigh about 2 grams, but they dont have 2 integrated DC motor ESC and 3 servo controllers, meaning the actual weight to get an equivelent to the Malenki Nano would be upwards of 10 grams. The Malenki Nano provides a 3 in one fuinctionality while being lighter than most standalone receivers and should be the pick for your project.

    Using a 2 cell battery for your 150 gram combat robot is optimal because the normal 150 gram robot will only need 2 cells to spin the weapon motor up to an apropriate speed because they are usually around 2,000 kV meaning that with a 2 cell battey, about 7.4 operating voltage, the weapon has a theortical max speed of almost 15,000 RPM, but taking into acount air resistence as well as other factors, this dips down to about 6,000 RPM. 6,000 RPM is more than enough speed for your robot to deal very good damage. The battery you purchase should also be between 200 and 300 mAh because from my own experience I have found this to be enough to leave your bettery at about 30% by the end of the fight as long as the weapon isnt full throttled the whole time, which is the reocmended minimum charge for a liPo battery.

    Motors

    Figure 9

    Selecting the correct motors for your combat robot is extremely important to getting a robot that drives well and hits hard. Using 2 turnabot n-10 motors for the drivetrain and a brushless hub mounted weapon motor of about 2,000 kV (see link above for my personal pick) works extremely well for a combat robot.

    A high-gear-ratio n-10 motor usually only weight about eight to ten grams according to ITGresa, and it provides more than enough tourqe to shove around 150 gram robots from what I have seen in my years in the sport. When compared to most other options for the drive motors, it provides superior strength to weight ratio and should be used in your robot.

    Using a brushless hub motor is optimal for the 150 gram robot because it minimizes the weight by getting rid of a lot of mounting hardware and doesn't have the downside of hubmotors in bigg weight classes because the 150s don't do enough damage to destory the hub motor like it might in larger weight classes. Hub motors do not have to be dedicated to that purpose from the factory. They can be made by taking a simple outrunner brushless motor and putting the weapon either directly on it or onto a spacer which safely connects the weapon to the motor. The advantages of this are explained by Maker’s Muse in his video A Combat Robot Weapon that NEVER STOPS SPINNING, saying that they “are phenomenally powerful for their size and weight” (Maker’s Muse 2024). This superior strength-to-weight ratio is what makes them the best choice for 150 robots.

    Mounting the hub motor onto the weapon can be extremely challenging to figure out how to do it without interfering with the weapons windings and mainting their lightness advantage. The easiet way to mount them together is to simply press-fit them together so that they may not come back apart, but if you choose to create a weapon with a thinned material, like 3/32 inch steel, it is much stronger to design a washer to hold them together. Figures 9 depicts such a washer and how it mounts the weapon to the motor for refrence when you are designing your robot.

    Drive Train

    Figure 10

    Choosing the apropriate drive train and components is extrmemly important to having a reliable robot that can control the match. Using a geared drivetrain with foam wheels coated in latex provides the best relability, least weight, and best traction for your combat robot.

    Using eva foam wheels for your combat robot provides the best weight for your robot, while still having more than enough traction thanks to the thin layer of latex. In the community it is gnerally a choice between lego tires and foam wheels because the lego tires are very easy to use, you just buy and mount them, but the lego tires can weight up to about 2 grams whereas the foam wheel will generally weigh only 1 gram with the latex and will have the same if not better traction thanks to the latex. This is further supported by Damao’s article Understanding EVA Foam Density & Hardness: Shore A/C. Explained where they state that high-density EVA foam, the most popular choice of foam for combat robotics, has a density of “150–280 kg/m³ [and that it is] stronger and more rigid” (Damao 2025). Considering that the average tire on a 150-gram combat robot is only about a half inch in diameter and three-eighths of an inch thick, that means that it only has a volume of 4.8 * 10^-6 m^3 and a mass of only about 1 gram. Combining this low weight with the grippyness of the latex, it become obvious why foam wheels shoudl be the choice for your robot.

    Geared drivetrain is the obvious pick for your combat robot because of the simple fact that combat robots need to be extremely to survive getting wailed on for 3 minutes straight and for multiple rounds at a time. When compared to the other option, such as belts, gear are the best pick due to their reliability. Gears dont carry the risk of snapping, stretching, or flipping in the event of your robot getting hit like a belt would. Gears are also much easier to replace due to their printed nature, the belts have to be bought beforehand, but because the gears ar 3D printed, they can be made in bulk in the event of a snap. This increased reliability and ease of manufacture and rplacment clearly places gears above all other drivetrains for 150 gram robots.

    A sample design for a geared drive train is shown in figure 10.

    CAD Models to Reference

    Work Cited