That old phone in your drawer already has a camera, a motion sensor and a processor. Researchers at UCLA used exactly those parts to run a walking humanoid robot. It's called PhoneBot, the hardware costs about $400 (phone not included), and the designs and code are open.
If you've wondered how real robots walk, or why humanoid robots cost as much as a car, this video explains it in under two minutes. You'll see what the phone does, what the legs do, how the robot learned to walk, and where it still falls short.
CHAPTERS
0:00 Meet PhoneBot: 48 cm, 1.8 kg, about $400
0:13 How the phone runs the robot
0:39 Learning to walk in simulation
0:58 Walking, following a person, getting back up
1:09 Old and $50 phones are enough
1:22 Limits, open source, and what comes next
WHAT PHONEBOT IS
PhoneBot is a small open-source humanoid from the Robotics and Mechanisms Laboratory (RoMeLa) at UCLA, the lab led by Dennis Hong. It stands 48 cm tall and weighs 1.8 kg with the phone. There is no separate robot computer for vision or balance. An ordinary Android phone sits on the hips and does that work.
WHY THE PHONE IS THE ROBOT
- Balance: the phone's IMU (its motion sensor) tells the robot how it is tilting.
- Eyes: the phone's camera runs on-device person detection and pose estimation, so the robot can see people and follow them.
- Brain: a neural network runs on the phone's CPU (TensorFlow Lite) and picks the next joint positions 50 times a second.
- No cable: the phone is not wired to the robot at all. Commands go over Wi-Fi (UDP) to a small onboard computer, which drives the motors. Because of that, you can swap in a different phone without touching the electronics.
THE LEGS: 13 SERVOS
Each leg has six servos: three at the hip, one at the knee and two at the ankle. A thirteenth servo turns the waist, so the phone can look around while the feet stay planted. All 13 are DYNAMIXEL XL430-W250-T servos, about $23.90 each, which makes them the biggest part of the bill.
HOW IT LEARNED TO WALK
The walking controller was trained in simulation (MuJoCo / MJX) with reinforcement learning (PPO). The simulator includes a model of how weak these low-cost servos really are, so the robot doesn't learn moves its motors can't make.
Early versions limped: one leg did most of the work. The fix was simple. Every training example was mirrored, so left became right. The gait balanced out, and the left-right joint mismatch dropped from 0.254 to 0.003 radians, about 99% lower. Training also got faster and more consistent.
The trained controller then went straight onto the real robot. In the paper's hardware tests, PhoneBot walks, tracks a person with its camera, and stands back up after lying face-down.
DO YOU NEED AN EXPENSIVE PHONE?
No. The team tested four Android phones: a used 2017 Honor 9 and three prepaid budget phones that cost about $50 to $80 (moto g 2025, Galaxy A16 5G and moto g 2024). All four ran sensing, control, vision and interaction on the phone itself.
For comparison, the paper lists other small research humanoids at about $3,500 to $13,800: HighTorque Mini Pi ($3.5K), Berkeley Humanoid Lite ($5K), ToddlerBot ($6K), BRUCE ($9K) and ROBOTIS OP3 ($13.8K).
THE HONEST LIMITS
- No arms yet, so it can't pick things up.
- It was trained to walk on flat floors only.
- The cheap servos limit how much it can carry and how dynamic it can be.
- Conversation (speech-to-text, the language model and the voice) still runs on a laptop, not on the phone.
The researchers say their next steps are uneven ground, lightweight arms, and running the language model on the phone itself.
WHO IS THIS FOR?
Students, teachers, makers, and anyone who wants a real walking robot to learn on without a five-figure budget. If you have an old Android phone in a drawer, you already own the most expensive-to-design part.
SOURCES
- Paper: Hou, Wang, Koh and Hong, "PhoneBot: A Low-Cost Open Humanoid Robot Platform Reusing Smartphones", arXiv:2610.08737 (2026): https://arxiv.org/abs/2610.08737
- Project page, hardware and code: https://phonebot.dev
- TechXplore: https://techxplore.com/news/2026-10-phonebot-smartphones-job-legs.html
- Hackster.io: https://www.hackster.io/news/don-t-throw-away-your-old-phone-build-a-robot-instead-392de07d053a
- heise online: https://www.heise.de/en/news/PhoneBot-Humanoid-open-source-robot-based-on-an-old-smartphone-11481931.html
ABOUT THIS VIDEO
The robot you see is our own 3D illustration based on the published joint layout. It is not footage of the real robot; you can see the real one on the project page. All numbers come from the paper. The narration is an AI voice (Gemini TTS), and the background music is AI-generated (Lyria).
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#PhoneBot #Robotics #HumanoidRobot #OpenSource #AI
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Your Old Phone Can Run a Walking Robot (PhoneBot, the $400 Open-Source Humanoid)
Humanoid Home News October 12, 2026 1:53 pm