Guide on Building Your Own Miniature BattleBot!

Hi everyone! My name is Alya, and I like to build cool stuff! As a simple intro into the world of battlebots, I decided to build my own miniature bot in Fusion 360.

For those who are not somehow aware what battlebots is, it's a TV show where robots of massive size and weight fight against each other. But, the world of combat robotics is not just limited to battlebots. There are hobbyist competitions all across the world, where anyone can compete in with their own bot.

On the lighter end of combat robots, there are three weight classes-

1. Fairy-weight bots - weighing under 150 grams and sometimes required to fit inside a 150mm cube
2. Antweights - weighing under one pound(453 grams)
3. Beetleweights- weighing under 3 pounds(around 1,360 grams)

These weight classes do change country to country, so google it up. These bots can have a variety of weapon attachments.

In this tutorial, I'll be focusing mostly on fairy-weights, but I'll provide a lot of info that might be useful to new builders like me. I'm sorry for how long this goes, but it is best you read it to make you life easier. If you want something concise, this is best. So, let's jump into it.

Before diving into the supplies, I'll explain some of the basic electronics used to operate a simple combat robot, and what they do. These explanation is quite non-technical due to my very limited experience. LET'S START!

So, in combat robotics, you need a transmitter, a receiver, motors, either a servo or a brushless motor for your weapon, and a LiPo battery.

A transmitter is basically a glorified RC gamepad or other device, similar to the ones kids use to control toy cars, but will contain way more knobs, switches, and buttons. Most transmitters are oriented towards drone makers, which is why they have so many of these. Each of the toggles, switches, and each of the x and y-axis of a joystick correspond to something that's called a channel. A channel controls the position/power of electronics such as your motors by providing a signal to the receiver(more on it later) based in the position of these input devices.

Before I explain more about channels, I want to talk about servos. For those who don't know, a servo is just a motor with gears that spin an "output axis". You can attach items to the axis, and instruct the servo to spin to a specific angle, usually between either 0 to 180/270 degrees. The servo, after reaching the target position, will stay at the same point. A servo uses a connector consisting of three wires, a power, ground, and signal wire. The signal wire will communicate the angle to the servo, while the power and ground cables will power the servo. The colors of the wires do differ, so do google it up.

Now, back to channels. So, a transmitter's channel can also provide a signal that controls the position of a servo. Some transmitter have as little as 4 channels, while some intended for drones can have up to 12! (I'll provide the link to the transmitter I bought, but I do not recommend it due to the price).

Next, I want to talk about receivers. So, when I explained transmitters, you might have wondered where we connect the electronics of the robot to so we can control then. A receiver serves this purpose for a robot. A receiver basically consists of a PCB with pins(which you might have to solder...) that allow you to connect the female ends of all your electronics to it. These pins are divided into "sections" of three pins vertically, corresponding to one channel. In these three pins, one corresponds to the channel signal provided by the transmitter, one gives out 5V power, and one serves as ground. This three pin layout uses something called PWM as the protocol to transmit the signal, but there are others such as s-bus, etc that use different layouts. These might be labeled on your receiver. You can either use the receiver included with your transmitter, but there are also standalone ones on Amazon that offer less channels and a lighter package. Servos can be directly connected to the receiver, but motors will require an ESC.

Additionally, I want to talk about ESC. ESC's(Electronic Speed Controllers), allow you to connect motors to a receiver. You need these because if you have ever looked at a traditional motor, they only have 2 pins used to supply power to spin the motor's shaft. For us to use the transmitter to govern the direction and speed of these motors, we require ESC's, which supply different amounts of voltage in different polarities to control the direction and speed of these motors. Some of these ESC's can control only one motor, while others can control two. ESC's that control one motor will take up one channel, while ESC's that support 2 will take up two channels.

Some things you will need to keep in mind while getting ESC's is if they support something called mixing, and the type of motor it is made for. Mixing basically uses the input from the two channels to control the directions of the drive motors. For example, let's say I use channel 1 and channel 2 on my receiver for my 2 motors. Moving the joystick up/down (which corresponds in Channel 1 in this case) will result in the robot moving forwards and backwards, while moving the joystick left/right(which corresponds to Channel 2 in this case) will result in the motors spinning in opposite directions (aka. rotating either clockwise or counterclockwise).

Additionally, the type of the ESC's matter. Essentially, there are two kinds of motors, brushed and brushless. I won't go much in detail(YouTube has good tutorials), but brushless motors are more expensive with higher torque, speed, efficiency, and overall lifespan compared to their brushed counterparts. These would usually be used to power the weapon on your combat robot, while brushed motors are often used for the motors on your drivetrain(aka. used to move your robot around). But, some robot's also use brushless motors instead of brushed motors in the higher weight classes for this purpose. When you are purchasing the ESC, you must keep in mind the type of motor. There are separate ESC's sold for brushless and brushed motors.

Finally, the last thing you will need to know about an ESC is something called a BEC(Battery Elimination Circuit). Basically, this allows you to connect the battery directly to the ESC, and not the receiver. Then, the ESC, which will use the same connector used by servos, to connect to the receiver and will power 5V to the receiver. If an ESC powers two motors, it will use two connectors to connect to one channel independently. One of these connectors will look similar to a servo connector, while the other will be one-pin and will connect to the channel pin only on your receiver.

Lastly, I must talk about LiPo Batteries. LiPo batteries are used to power your bot, but they're quite dangerous. They can explode, resulting in a fire that cannot be put easily, so be very careful with these.

I'll first start off by talking about the numbers on the cover of a LiPo battery. Basically, a capacity of a LiPo battery is rated in mAh, such as 5000 mAh. This basically means that I can pull 5 Amps of current total in one hour, 2.5 Amps total in 2 hours, etc. The battery will be fully empty after this (do not actually fully empty the LiPo, this will permanently damage it and render it useless). An S number is also provided, representing the number of cells the battery has. For example, a 2S battery will have 2 cells.

Finally, you have a C number which indicates the discharge rate. You multiply the (mAh number divided by 1000) • (the C number) to get the current that the battery will output. For example an 80C, 1300mAh LiPo can output 80*1.3 = 104 Amps. Make sure you treat your LiPo with respect, or it'll burn your house down. Seriously. Store it in a LiPo safe bag to minimize damage in case of a fire, and dispose it safely if it is fully dead. A LiPo is considered dead if its voltage drops below 3V per cell, at which point most chargers won't charge it. There are workarounds to restore it to a usable state. But, the usual rule of thumb is to stop playing with your bot and charge your battery if the voltage drops to around 3.7 volts per cell.

Check out this guide for even more info, plus an intro to Combat Robot Weapons!

You Will Require - Sourced from Amazon

Links are what I used for this project

1. A 3D printer (recommended), but a service such as JLCPCB is also fine
2. A Transmitter - An example (not recommended)
3. (Optional) A Lighter Receiver
4. Countersunk Screws - I recommend an assortment of M4 screws
5. TPU and PETG/PLA - I recommend this brand
6. A LiPo Battery - I recommend a 2S battery
7. A LiPo Safe Bag
8. A LiPo Charger - Better options are definitely available, but this is a simple, budget-friendly model.
9. Soldering Iron Kit - You can also get solder with lead, which is easier to use for beginners
10. A Multimeter / LiPo Charge Checker

Sourced from Combat Robotics Parts Retailers

For the parts here, I recommend you source them from online stores such as BBB or Turnabout, as they offer kits that contain all of these parts at a reasonable price. These kits might even include some of the above components. Amazon does not have ESC's that are suitable for combat robotics, so I would recommend you use another retailer.

1. An ESC
2. Wheels
3. 2 N20 Motors (Turnabot offers excellent N20's with exceptional specs. Please get them if you can).
4. (Optional) N20 motor mounts

Basically, CAD stands for Computer Aided Design, and software such as Fusion 360 and Onshape assist you in designing your robot with various features. If you are a newbie to all of this, I would recommend you check out YT tutorials to learn the basics, and do plenty of practice designing items, from simple keychains to working your way up to projects such as this one. Don't worry, it won't take too long, but will require 1-2 weeks of you maybe spending a hour a day to get the hang of CAD. Fusion 360 is the CAD program you should check out if you have good hardware at hand, and the one that use. There are plenty of tutorials to help you get started on YouTube. If you don't though, I recommend Onshape, a web-based CAD program that is less hardware and space intensive than Fusion. It also has plenty of tutorials to learn, but it has less than Fusion. These are just my personal recommendations, so make sure you do some research to check out different CAD programs online.

I would recommend you start off with a base sketch which draws out the layout of your bot, plus draw where you plan to place the various components. For the base of your bot, you can either divide it into a base(where the components go) and a top plate like my bot, or use two plates and sandwich the base in-between. What you pick usually depends on your weapon of choice, so pick wisely. MAKE SURE YOU LEAVE PLENTY OF TOLERANCE FOR THE SPACES IN WHICH YOU PLAN TO PUT ALL OF YOUR COMPONENTS!

One tip I have(I learned this the hard way...) is that you give around 3-5 mm additional space length-wise for where you plan to place your receiver. This is due to the connectors you will plug into it, which extend out outwards. Make sure you also give at least 1 - 1.5mm of tolerance on all sides for where you plan to place your wheels. For other components, I would recommend that you pick the most appropriate tolerance based on the wires that protrude out of it, and based on if the component should be either firm in place or allowed to move around slightly. Allowing components to move around slightly may help the robot distribute impact better if it is hit in any manner.

Screw holes also need to be toleranced. If you plan on using a material such as PLA(more on 3D printing materials later), make sure the screw hole is a bit smaller that the diameter of the screw, by about 0.2 millimeters, but this will change 3D printer to printer. If you plan on using TPU or something else, I find making the screw hole 0.5 - 0.6 millimeters smaller than the diameter of the screw does best.

For information on Combat Robot CAD Techniques and more example robot projects, please check out Maker's Muse on YouTube, who have excellent tutorials for beginners that go in detail explaining everything from the materials he used to 3D print the robot to more about tolerances for the different parts of the robot.

Then, extrude your walls and other parts of the top and the bottom of your base. For more experienced roboteers, I do not recommend that you pocket the top cover of your robot, as that will increase its weight. Maker's Muse has a good video explaining why.

Start drawing out your other external components for your weapon assembly or other needs on sketch, using mounts you added onto them from the previous stage. Then, extrude them all, and make them separate components. Make sure you use joints/mates to attach them to the base!

You can find the CAD of many common components online, and CAD a rough design yourself for the rest. I used this page for most of these components, and Grabcad for the ones remaining. This allows you to see how everything fits together, and adjust the dimensions of the robot to fit them better if something does not fit. My assembly of the components is quite rough, so y'all can definitely do better than me.

So, I want to kinda introduce you to the different materials you can use to 3D print the robot. For the robot body, I recommend TPU for your bottom/center body part. TPU is flexible, so it deals with impact well unlike other filaments such as PLA, which is a rigid type of 3D printable plastic. For your plate(s), to hold the TPU base together rigidly in place, I would recommend they be printed in PLA/PETG. PLA is the most commonly 3D printed material due to its ease of use(it almost always prints perfectly), so it is perfect for beginners. PETG is stronger than PLA, but it is harder to print, and can require the user performing calibrations to figure out the settings to get the best prints. There is more information available about 3D printing on YouTube about materials, calibrations, and other aspects so please do some research.

Here comes the most dreaded part...The soldering. If you don't know what soldering is, soldering is the process of joining two metal surfaces together using a metal called solder. You use solder to attach wires to components mainly in your, and for other processes to connect everything together. There are several good quality videos available on YouTube that explain this process, and specific soldering skills you will need to for working with electronics in general. This is the one I used. This is a guide I used to connect all the components together, and you can adapt it to put your respective components together.

Cut off much extra wire as you can to save weight, but if you can't you can even use thin rubber bands or small zip ties to wrap up the extra wire in a compact package.

I mean, this step is pretty self explanatory.

I don't have any videos of my bot driving unfortunately due to my negligence. The receiver I used(linked in supplies), does not support telemetry(aka. I couldn't see my battery voltage on my transmitter), and my battery voltage dropped to

I hope y'all enjoyed this guide. If you liked it, please leave a heart, and if you want me to fix anything, leave me a comment.