After a run of wheeled and legged walkers, I wanted something that looked more like an animal. Something with four legs that could walk, dance, maybe even hop. I found MiniKame, an open-source quadruped designed by Javier Isabel back in 2016.

We built the newer Kame32 version, which swaps in an ESP32 and uses cheap SG90/MG90s servos instead of the expensive high-voltage servos from the original. The kids named it Kame — which, as they were delighted to learn, means "turtle" in Japanese. It doesn't look much like a turtle, but the name stuck.

Why this robot

MiniKame has been around for nearly a decade and has hundreds of replicas out in the wild. It was featured on Hackaday back in 2016, and the community around it is still active. That kind of track record matters when you're building with kids — you want a project where someone has already hit and solved every problem you're about to hit.

What makes MiniKame special is its leg design. Each leg uses a parallel leg mechanism (PLM), which means the feet stay parallel to the ground throughout the entire range of motion. It's the same idea used in some RC cars and Japanese humanoid robots. The result is a much smoother, more natural-looking walk than you'd get from simple two-joint legs.

The build

The Kame32 redesign is optimized for parts you probably already have. The body houses eight SG90 or MG90s servos — STL files are included for both — and an ESP32 dev board handles the brains and Wi-Fi. Javier also designed a custom PCB that makes wiring much cleaner, and you can order it from PCBWay for a few dollars. I didn't want to wait so I hand soldered a board using some buck converters. Since space inside the enclosure is very tight, Javier recommends right-angled pins for the servo connectors. I had to order these special for this project.

Printing took about four hours total. Everything fits on a standard build plate and prints in PLA with no supports.

Assembly is where this project really shines as a kids' activity. Each leg is its own little sub-assembly: two servos, a few printed linkage pieces, and some tiny screws. The kids can build a leg start-to-finish and see exactly how it articulates before moving on to the next one. There are optional F693ZZ bearings at the joints for smoother movement, but the design also works with printed bushings if you don't want to order bearings.

The trickiest part is fitting everything inside the body. Kame is small, and the wiring gets tight once you have eight servos, an ESP32, and a battery crammed in there. After multiple failed attempts to cram everything in, including some where the wires shorted due to my shoddy soldering job, I decided to cut a hole a the top of the body and used the excess servo wires as the robot's "hair". I'd recommend cutting servo leads to length rather doing what I did.

How it moves

This is where Kame gets really interesting. The walking gaits aren't pre-programmed sequences — they're generated in real time using oscillator-based algorithms. Each leg's motion is defined by a set of sinusoidal oscillators with different amplitudes, frequencies, and phase offsets. By tweaking these parameters, you get different gaits: walking, trotting, turning, and even hopping.

The kids don't need to understand the math to appreciate the result.

Control is over BLE and I used Claude Code to build and refine an iOS app to control the robot.

What you'll need

• 8x SG90 or MG90s servos or a mix
• 1x ESP32 dev board
• 1x 2S LiPo battery, I used the 300mAh battery often used in mini drones
• M3 screws

Total cost is around $20–25 if you order servos from AliExpress, or $35–40 from Amazon. This is one of the cheapest robot builds we've done that still feels genuinely impressive.

Tips for dads building this with kids

• Center all your servos before assembly. Flash the centering sketch to your ESP32 first, plug each servo in one at a time, and mark the center position on the horn. Skipping this step will haunt you.
• Let the kids build the legs — they're self-contained and satisfying. Save the body wiring for after bedtime.
• MG90s servos are worth the small price premium over SG90s. The metal gears are more forgiving when kids inevitably push the legs by hand while the robot is powered off.
• If a gait looks jerky or asymmetric, one of your servos is probably not centered correctly. Re-center it before you start debugging the code.

Recommendation

Here's my experience building the robot with the kids:

Concepts learned: Parallel linkage mechanisms, oscillator-based gaits, servo centering and calibration, Wi-Fi control, PCB assembly, inverse kinematics (conceptual)

Get started

Download the Kame32 3D files from Printables:

https://www.printables.com/model/1307752-kame32-next-gen-minikame-with-esp32

Firmware and source code:

JavierIH/kame32 (recommended — the newer ESP32 version)

JavierIH/miniKame (the original ESP8266 version)

And check out Javier's project page for background on the original design and videos of MiniKame in action.

You can check out my version of the firmware and iOS app here: phmagic/kame-robot