How to build a shitty robot

{ Mario Zechner }

developer • coach • speaker

How to build a shitty robot

2026-05-30

"What is my purpose?"

Table of contents

Disassembly using violence<br>Reverse engineering the PCB and mechanics<br>Big plans<br>Rewiring the electronics<br>Cardboard engineering<br>The boring softwareSpeech to text<br>Text to speech<br>Getting the speech pipeline right<br>LLM and agent

How 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...