Geeks Build Cabbage-Priced Biped Robot for Under 3,000 Yuan, with Old Phones as Key Contributors

UCLA's RoMeLa lab recently introduced PhoneBot, a biped robot 483 mm tall, weighing 1.8 kg, with 13 degrees of freedom. Each joint uses a servo that costs $23.9. A smartphone is fixed to the torso and serves as the sensor suite, onboard computer, and user interface. The robot can walk, stand up, follow people, take photos, and hold conversations. Testing used older models such as the Moto G2025 and Samsung Galaxy A15, which sell secondhand for about $100 or less. Even including the phone, total materials cost is under $500, or roughly 3,000 yuan. Motion control works as follows: an Android app reads the phone's gyroscope and accelerometer along with the current angles of the 13 motors, and a pre-trained small model computes the target position of each leg, then sends commands over Wi-Fi to a small converter board that drives the motors. Walking, standing up, and turning are all handled this way. Image recognition and localization run entirely on the phone, using the rear camera and sensors. Speech-to-text and large-model inference are handled by a laptop placed nearby. CPU load on the phone is about 6-10% for gait calculation, 16-18% for person and object recognition, and 25-34% for localization. PhoneBot is an experimental platform with no arms, no payload capacity, and no stair-climbing ability. Still, treating old phones as replaceable robot brains with a durable body could lower barriers for developers and create a modular model. As on-device AI chips improve, the reliance on external PCs for speech processing may also decline.