How to build a shitty robot

2026-05-30

"What is my purpose?"

Disassembly using violenceReverse engineering the PCB and mechanicsBig plansRewiring the electronicsCardboard engineeringThe boring softwareSpeech to textText to speechGetting the speech pipeline rightLLM and agentHow it started, how it's going

Last Friday I went to the toy store with my boy, and while he was rummaging through the Spider-Man section, my eyes caught sight of a section with very low-cost toy robots. As I'm playing with agents, LLMs, speech-to-text, and text-to-speech, I thought: why not buy myself one of these low-cost robots, take it apart, and turn it into a fun little LLM-powered toy for my kid and possibly the other kids in the hood? Or even better: turn it into a STEM learning project that the other parents in the hood and I can do with our kids. That means keeping the work super simple and only using materials that are readily available. There might be some soldering, but I can do that for everybody else. I went ahead and bought a Silverlit YCOO NEO OCTOBOT (also on Amazon) for 10 euros, which looks like this.

The box set. It has a full LED matrix.

The little robot came with a remote that lets you turn its head counterclockwise or move it forward in the direction it's facing. There was also a little dance button that just randomly turned its head and moved it forward, and some other buttons I didn't even try. The arms are non-functional. You can pose them, but that's pretty much it. Also, that LED matrix is actually not an LED matrix, but more on that later. First task, disassemble the thing and figure out how it works. Disassembly using violence Being the craftsman I am, I naturally didn't have the watchmaker screwdrivers I needed to unscrew the eight-ish or so screws. So instead I used violence.

As it turns out, the advertised LED matrix display was just a few RGB LEDs and a printed inlay on top of it. The inlay is a sort of translucent printed piece with a pixelated rainbow grid and two black eyes on it, with a clear plastic dome sitting in front.

The LEDs just shine through it from behind.

With the display removed I had access to the PCB's front side, which showed me a rather trivial layout and set of ICs.

I went ahead and ripped off the top of the robot, leaving me with just the legs, the motor driving them, and the battery bay sporting three triple A batteries. Then I started to trace out the PCB to understand it. Reverse engineering the PCB and mechanics The PCB turned out to be really, really simple. I suppose Chinese electronics toys all have this quality to keep costs down. And some of the design was kinda impressive to me as a layman who doesn't have a lot of experience with electronics or mechanical design. Here's the PCB.

In the top left you see the battery connector, which on the back is connected to two capacitors that just make sure the motor gets enough juice in case they stall or draw more power than expected. The big IC in the middle is the brain. It handles communication with the IR receiver on the middle right, controls the LEDs on either side, and drives the H-bridge, which is the tiny black chip at the bottom. Interestingly enough, the PCB is a single layer board. If you look closer, you can spot two zero ohm resistors used as little bridges over traces that would otherwise cross.

For me this meant I could just remove the stupid brain IC, which I didn't need, and basically just hijack the H-bridge. But there was one mystery left. There's only one motor in the robot, but the robot can either walk or turn its head. And the H-bridge only has two of its outputs connected to that motor. So how could the robot turn its head and move forward with just a single motor? Here's how.

The design is rather simple. There are two sets of gears, and depending on the direction the motor is turning, either one of them is engaged. In the back, a tiny gear rotates the top platform, which sets the walking direction via what I can only describe as a transmission. Then if you reverse the motor, the legs move in the direction set by that gear. I found this super genius. Of course, this also means the robot can only walk forward and can only turn in one direction. Big plans Now that I understood how the whole thing works, I started forming a plan.

Since I had promised my boy we'd try it out the next morning, I had to move fast. And since I don't have my 3D printer at home, any chassis would have to be built from whatever I had around. That means cardboard. The next decision was that I'm not going to use my trusty ESP32 boards or one of the dinky little displays I can drive with them, but instead just use my phone as the display and brain of the robot. With that as a constraint, I had to think of how the phone could control the motor for the rotation and the legs. Luckily enough, I have an Adafruit FT232H at home.

The FT232H can be connected to a phone or computer and gives it kind of the same capabilities that you have on a Raspberry Pi, for example. Specifically, you can use some of its pins as GPIOs, meaning you can send signals into a circuit programmatically. This is exactly what we need to drive the motor driver on the robot's PCB. That just leaves us with the software. I could have tried to cram everything into the phone with a native app, but having suffered through Android development in the 2010s, I really didn't want to do that. Instead, I opted for a client-server architecture. The server runs on my laptop and is the actual brain of the robot. It manages speech-to-text, text-to-speech, the LLM, and the agent itself. The ultimate goal here is to have all the machine learning models run locally, so any interactions of my boy with the robot stay private. The phone is then just a dumb renderer, exposing audio input and output to the server, as well as tools like taking a photo or driving the motor via USB. Both the server and client side run on TypeScript. On the server I use Node, and the client is just a website served by the server. That in theory makes the client run anywhere there's a browser, except Safari on iOS, because that obviously doesn't implement WebUSB. Because Apple hates the web. On the UX side, I wanted it to be a friendly, playful, non-sycophantic voice assistant my boy (and other kids in the hood) can talk to and have fun with. It doesn't take a lot to entertain young children, so I didn't want to add too many features.

The kids should just be able to speak to it naturally: ask questions, request jokes or stories, have it search the internet, take a photo to read text out loud, play music on Spotify, and obviously walk and turn. I also want the robot to have simple memory, so it can remember past conversations. I wanted the experience to be as seamless and intuitive as possible, so the speech-to-speech pipeline had to be as good as I can make it within the time constraints of one or two nights. Rewiring the electronics This part sounds kinda scary to the uninitiated, but if you have used a soldering iron and a heat gun before, it's actually really easy. First we need to decapitate the existing robot's PCB. That means getting rid of the big fat black mystery IC. For that I use my trusty heat gun with about 250 degrees Celsius.

It doesn't quite matter if the resistors and caps next to the chip go belly up as well during that process. You just need to make sure that nothing around the H-bridge at the bottom gets fucked up. Next I soldered two 10cm pieces of wire-wrapping wire to the two top pins of the motor driver.

This can be a little finicky. If you manage to bridge the pins, don't worry. You can use some solder wick, a piece of copper braid you put on top, to get rid of the excess solder. I use a standard soldering iron with leaded solder at 350 degrees Celsius. See my Boxie blog post on the exact gear I use. Next I soldered those two wires to pins D4 and D5 on the FT232H board. We can then bit-bang those pins via USB to drive the motor. And finally I soldered another piece of wire between the ground pin on the FT232H board and the ground pin on the robot's PCB for common ground.

The mystery IC is still on in this picture. Just ignore it.

And that's all the soldering you need to do. Once that was in place, I had my little coding agent write a single-page HTML file to test the full chain from WebUSB through the FT232H and H-bridge to the motor.

Great success. The wiring was correct and I could drive the motor from WebUSB.

Onwards to the chassis design. Cardboard engineering Time to construct the new upper body from cardboard. The first thing I actually did was use double-sided tape to create a sandwich of the battery bay I retained from the original robot, the PCB of the original robot, and the FT232H. So I have a snug little package I can put in whatever chassis I have.

I used some Kapton tape between the FT232H and the original PCB for isolation. You put it between boards to stop them shorting each other. I also used some tape to reel in the wires. But then I got stuck. The round base kinda didn't make sense to me as a chassis, and I couldn't figure out how to mount both the package and the phone on it.

That was until my wife burst in, looked at the thing for one second, and then did this.

I'm obviously married to a genius. It didn't occur to me that I could just put a cup on top of that. She then found a better fitting paper cup, slightly smaller, which I cut a hole into with a craft knife to fit the little package.

I also did a little cutout at the top of the paper cup so the USB port was accessible and through which I could thread the cable from the motor to the original PCB. I then stuck some double-sided tape onto the base of the robot as well as on the lower rim of the paper cup to stick them together.

For my final trick I just had to design the top of this abomination. Since the top rim of the paper cup was nicely horizontal, that was rather easy. I took some cardboard, made some measurements, and then cut to taste.

You can probably derive how this fits together from the images. I used some double-sided tape to secure the fold-ins. Then I put some double-sided tape at the top rim of the paper cup and at the bottom of the top part so those stick together nicely as well. And one more tiny piece of double-sided tape at the front of the top part where the phone sits, so it gets a little stuck there and doesn't fall off. Here's the result.

I'm very happy with this construction. The only part that requires parental help is the craft knife work, but everything else is totally child friendly, including wiring things up.