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PhoneBot is an open-source humanoid robot platform that uses an Android smartphone as its main sensing, vision, and onboard computing unit. The design has 13 degrees of freedom: six actuated joints in each leg and a torso yaw joint. A 2026 arXiv preprint by Ruochen Hou, Quanyou Wang, Daniel Koh, and Dennis W. Hong presents it as an affordable, reproducible way to build a legged robot without designing a separate sensor and computing stack. It is a platform for education, research, and prototyping that readers can reproduce or adapt. It is not a finished consumer robot, and the sources do not show that it solves electronic waste.
What PhoneBot is
The project’s central idea is that a modern phone already contains most of the parts a small robot needs: an inertial measurement unit, a camera, a processor, a display, and a microphone. Instead of wiring these up separately, PhoneBot mounts the handset on the torso and lets it do the thinking. The authors state the goal directly in the paper’s abstract: “With fully open-source hardware and software designs, PhoneBot provides an affordable, reproducible platform for education, research, and rapid prototyping.” That quotation comes from the author group, not from an interview with any one author.
The preprint was posted to arXiv on 6 October 2026. A report by Ingrid Fadelli for Tech Xplore / Phys.org followed on 8 October 2026. The PhoneBot project website links to the preprint and contains little additional text, so the paper is the place to check technical details.
The body: 13 degrees of freedom on two legs
According to the preprint, the assembled robot measures 483 × 183 × 125 mm and weighs 1.8 kg. That mass includes the phone, actuators, structure, electronics, and battery. An independent report published on 8 October 2026 describes the robot as about 48 cm tall.
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- Dimensions: 483 × 183 × 125 mm assembled (Hou, Wang, Koh, and Hong, 2026).
- Mass: 1.8 kg, including the handset, actuators, structure, electronics, and battery (same source).
- Degrees of freedom: 13 in total, all of them servo-driven joints except where the paper says otherwise.
- Actuators: the paper specifies the DYNAMIXEL XL430-W250-T servo motor for all 13 joints.
Leg joints
Each leg has six actuated joints. Together they give the robot the range it needs to walk, track a person, and rise from a fallen position, the three behaviours the authors demonstrate on hardware.
The torso yaw joint
The thirteenth joint is a torso yaw joint. It rotates the upper body, and with it the phone camera, without turning the feet. A robot with this joint can look toward a person while its legs keep a stable stance, which matters for the person-tracking demonstration.
How the phone and the robot share the work
The split of responsibilities is the key design choice. The phone is not a remote control; it runs the control logic and reads the sensors that the robot depends on. The sequence the paper describes runs as follows:
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- The phone reads its own inertial measurement unit and captures frames from its camera.
- The phone runs the locomotion policy and the vision functions of the application.
- The phone sends joint-position targets over Wi-Fi to a small onboard computer.
- The onboard computer forwards those commands to the servos.
- In the current setup, speech recognition and language processing run on an external laptop, not on the phone or the onboard computer.
This arrangement keeps the phone’s sensors close to the controller while leaving the actuator electronics on a separate board. It also means the robot depends on a wireless link between the phone and the onboard computer, so Wi-Fi quality is part of the control loop.
Build cost and parts
The reported hardware estimate
Tech Xplore / Phys.org, citing the researchers, reports a hardware cost of roughly $400. That figure is an estimate and excludes the smartphone. It is not a current price quote, and it does not account for shipping, tax, tooling, or the cost of a laptop for speech processing. Readers should treat it as a rough order of magnitude for the parts in the paper’s design.
The actuators are the main expense
The paper identifies the servo motors as the platform’s primary expense. Readers who want to reproduce the robot should use the DYNAMIXEL XL430-W250-T specified for all 13 joints and follow the project’s own design and compatibility details. The sources reviewed do not establish that a complete PhoneBot kit is sold, so assume you will be sourcing parts yourself.
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Which phones were tested
The paper’s application was tested on four Android phones. It reports that all four handled the core application functions. Only one phone is named in the sources reviewed, and the results for the others are limited to the summary above.
| Phone | Core application functions | ARCore SLAM |
|---|---|---|
| Honor 9 (2017) | Handled | Did not work in the United States, because Google services were unavailable on this Huawei device there |
| Three low-cost Android phones (not named in the sources reviewed) | Handled | Not stated |
Four phones is a small test set. It shows that the application can run on more than one handset, but it does not establish that every Android phone will work. Check ARCore support and Google services availability on your own device before you build around it.
What the demonstrations and tests show
Physical demonstrations
The paper reports three physical demonstrations: walking, tracking a human, and standing up from a fallen position. These are hardware results, and they are the strongest evidence for the platform working as a whole.
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Locomotion training with mirroring
The authors compared locomotion training with and without sagittal mirroring, which reflects the training data left to right. Each condition used five independent random seeds. In simulation, the authors report that mirroring improved learning speed and consistency and reduced simulated gait asymmetry. They also report deploying the resulting controls on the physical robot.
The simulation results describe how the training behaved in a virtual environment. They are not measurements of real-world gait on the physical robot, and the paper does not present a side-by-side physical comparison of mirrored and non-mirrored controllers in the sources reviewed.
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- Terrain: the reported locomotion training was on flat ground. Uneven-terrain walking is listed by the authors as future work.
- No arms: the current robot has no arms and does not manipulate objects.
- Payload and speed: the independent report notes that the inexpensive motors limit payload and the vigor of movement.
- Speech: spoken interaction is supported, but recognition and language processing run on an external laptop in the current setup.
- Not an autonomous helper: nothing in the sources supports describing PhoneBot as a household robot that performs tasks independently.
How it compares with OpenBot
OpenBot, described by Matthias Müller and Vladlen Koltun in a 2020 arXiv preprint, is an earlier smartphone-powered platform. It is a wheeled robot, and its paper reports a $50 body and demonstrations of person following and real-time autonomous navigation. The comparison is useful because both projects use a phone as the robot’s brain, but their mechanical and control problems are very different.
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| Attribute | PhoneBot (Hou, Wang, Koh, and Hong, 2026) | OpenBot (Müller and Koltun, 2020) |
|---|---|---|
| Body type | Biped with 13 degrees of freedom | Wheeled platform |
| Reported body cost | About $400 hardware estimate, excluding the smartphone (reported in 2026) | $50 body (2020 paper) |
| Demonstrated tasks | Walking, human tracking, standing up from a fallen position | Person following, real-time autonomous navigation |
| Mechanical and control demands | Higher: the robot must balance and stand on two legs | Lower: wheeled locomotion |
The two cost figures should not be compared directly. They come from different years, different robot configurations, and different scopes, so a dollar difference between them says little about which design is cheaper to build.
Who should look at PhoneBot
PhoneBot is most useful for students, teaching labs, and prototypers who want a legged robot with onboard sensing and do not want to design a separate sensor and computing stack. Its open-source hardware and software designs are the main reason to study it. Before you start, confirm that your phone supports the features you need, plan for a separate laptop if you want speech interaction, and design your experiments for flat ground and a robot without arms.
Quick Recap
Sources
- Ruochen Hou, Quanyou Wang, Daniel Koh, and Dennis W. Hong, “PhoneBot: A Low-Cost Open Humanoid Robot Platform Reusing Smartphones,” arXiv preprint, posted 6 October 2026. This is the primary technical source.
- Ingrid Fadelli, “PhoneBot gives old smartphones a new job on two legs,” Tech Xplore / Phys.org, 8 October 2026. The cost figure is a reported estimate.
- PhoneBot project website, accessed 9 October 2026. It links to the preprint.
- Matthias Müller and Vladlen Koltun, “OpenBot: Turning Smartphones into Robots,” arXiv preprint, posted 24 August 2020. This is the source for the historical comparison.
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