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YOU CAN BUILD A PALM-SIZED ROBOT DOG THAT DOES BACKFLIPS

A quadruped robot small enough to hold in one hand that walks, runs, balances on two legs, and does backflips — and you program every move.

by Petoi (Rongzhong Li and team)

FULL CAD BOM FIRMWARE DOCS

RoboticsOpen-hardware

Built withArduinoRaspberry Pi

difficulty
●●●○○
time
a weekend-plus
license
MIT
repo
repo ACTIVE5,414 stars

WHAT YOU’LL NEED

1
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COMPAREE VERDICT

Bittle is a serious robotics platform dressed as a toy dog. The OpenCat firmware lets you program gaits, reactions, and tricks in Arduino C++ or Python, and the community has already written skills for voice commands, object tracking, and remote control. The backflip is real — it is a pre-programmed sequence you trigger, not something you teach from scratch — but writing your own behaviours is where the weekend disappears. The kit build itself is straightforward if you have ever assembled a complex model, but calibrating eight servo motors so the legs move in sync is the part that will take longer than the instructions suggest. Most people underestimate how much trial-and-error goes into making a quadruped walk smoothly. If you want a platform to learn inverse kinematics and gait planning without building the chassis from scratch, this is it. If you expected to design and 3D print your own robot dog, you are in the wrong project — the mechanics are closed and you are buying them.

GOOD TO KNOW

  • —OpenCat is the firmware framework, not mechanical files — Bittle itself is a commercial kit you buy assembled or unassembled
  • —This repo holds the Arduino (NyBoard) firmware, module tests, calibration tools, Python API and Raspberry Pi support; firmware for the current ESP32-based Bittle X lives in the separate OpenCatESP32 repository.
  • —No STL files — the mechanical design is proprietary to Petoi, the software stack is open
  • —Licence is MIT for the firmware, which permits commercial use with attribution.
  • —Active repo with a large community: Petoi reports 30,000+ robots shipped in 60+ countries and 20+ academic papers citing the platform.
  • —You can also buy a fully assembled version if you want to skip mechanical build entirely and go straight to programming

Parts to buy

2 items

From our check of the build. Exact quantities and part numbers are in the creator’s BOM.

  • Bittle kitFind
  • Arduino IDE or Raspberry Pi for programmingFind

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Can I build this?

Printnothing required — Bittle is a purchased kit, mechanical files are not open
BuyBittle kit (unassembled or assembled versions available from Petoi), plus Arduino IDE or Raspberry Pi for programming
Toolssmall screwdriver set for kit assembly, USB cable for firmware upload, computer for calibration and code upload
Skillsintermediate — assembly is model-kit level, programming requires Arduino/Python comfort and patience for servo calibration
TimeA weekend-plus: kit assembly, then IMU and joint calibration, which is iterative and usually takes longer than people expect; custom behaviours take as long as you want.
Cost$$ — kit price dominates, no additional hardware needed unless you add sensors or a Raspberry Pi for advanced features
SafetyNone beyond ordinary electronics care — low-voltage servos, no sharp edges, safe for a desk. Keep small screws away from young children during assembly.

Build at your own risk. Projects involve tools, electronics and sometimes mains voltage — follow the creator’s safety notes.

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Start here

Navigation into the creator’s own docs — we don’t rewrite the guide, we route you to the source.

  1. 1.Read the OpenCat README, then pick the right codebase: this repository covers the original NyBoard Bittle, while the current Bittle X (BiBoard/ESP32) uses the OpenCatESP32 repository (firmware and API are all here, but mechanical files are not — you buy the kit from Petoi)
  2. 2.Order the Bittle kit (assembled or unassembled) directly from Petoi(Not sold through the GitHub repo. The original NyBoard Bittle is discontinued; new kits are the Bittle X, which uses the OpenCatESP32 firmware. Check Petoi's site for current availability.)
  3. 3.Follow the assembly guide if you bought the unassembled kit, then upload the calibration sketch(calibration takes longer than assembly — every servo needs individual tuning for smooth movement)
  4. 4.Install the Arduino IDE or set up the Python API, upload the OpenCat firmware, and start with the example gaits(the backflip is one of the included skills — you trigger it, you do not write it from scratch)

KNOWN ISSUES

  • Bittle is a commercial kit with open firmware, not a fully open design — you cannot 3D print the body or source the servos separately at the same cost
  • Servo calibration is the single longest part of the build and the instructions make it sound faster than it is — expect to iterate
  • The backflip and other flashy moves are pre-programmed — writing your own complex gaits requires solid understanding of inverse kinematics
  • If a servo arrives misaligned or drifts after assembly, recalibration is fiddly — keep the calibration sketch and notes handy
  • The Python API requires a serial connection and is slower than direct Arduino control — pick your control method before you start coding
  • Community support is active but scattered across Discord, forums, and GitHub issues — finding answers takes patience

Can I 3D print my own Bittle instead of buying the kit?

No — the mechanical design is proprietary and the STL files are not published. The OpenCat firmware is open, the chassis is not.

Do I need a Raspberry Pi or can I use just Arduino?

The robot's own board is enough for all the core gaits and skills — an Arduino-compatible NyBoard on the original Bittle, an ESP32 BiBoard on the current Bittle X. A Raspberry Pi adds computer vision and other extras, but it is optional.

How hard is it to make Bittle do something custom, like fetch a ball?

Object tracking requires a camera and significant coding — the framework supports it, but you are writing the behaviour from scratch. Simpler tricks like sit, roll over, or play dead are easier starting points.

What happens if I break a servo during assembly or testing?

Petoi sells replacement servos, but they are specific to Bittle — generic hobby servos will not fit without modifying the frame, which is not designed for it.

Community builds

No community builds yet — be the first, we feature the best ones.

Discussion1

FROM THE COMPAREE TEAM

OpenCat runs on Arduino-based boards with Raspberry Pi as an optional AI co-processor, and the backflip is the skill everyone tries first. What would you teach yours to do after that?

CompareeTEAM2mo agoedited

Practical notes from our verification: OpenCat is the open-source framework (MIT licence) — firmware, calibration tools, Python and app control — while the Bittle and Nybble robots themselves are Petoi's commercial kits. Note that this repo now covers the legacy NyBoard (ATmega328P) platform; for current hardware such as Bittle X and Nybble Q, the README points you to OpenCatESP32. The time everyone underestimates is calibration — IMU calibration plus joint calibration via the serial monitor or the Petoi app — it is not hard, just iterative. The backflip is a pre-built skill, so you get it working quickly, but writing your own gaits from scratch is where the learning curve lives. If you want to program robot behaviour without fabricating the chassis, this is a solid choice. Correction (4 October 2026): we re-checked this page line by line against the project's own repository, documentation and videos, and fixed errors in earlier versions.

Petoi (Rongzhong Li and team)

Rongzhong Li started OpenCat in his dorm at Wake Forest University in 2016 to make agile quadruped robots affordable and hackable. Petoi later funded its kits through Kickstarter and Indiegogo, and the framework grew into a widely used teaching platform for schools, universities and hobbyists.

GitHub

Star the project on GitHub

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