What Is PhoneBot? UCLA's Smartphone-Powered Walking Robot
PhoneBot from UCLA's Dennis Hong lab uses a $50-80 used smartphone as the robot's brain. Here is how it works, how it recovers from falls, and what it costs.
What is PhoneBot?
PhoneBot is a small walking robot from Dennis Hong's robotics lab at UCLA that uses an old smartphone as its brain. The phone is not a remote control. It is the robot's controller and sensor package: the camera acts as the eyes, the motion sensors handle balance, and the walking AI runs on the phone itself. The phones cost roughly $50 to $80 used. The body costs about $400, and the team is open-sourcing the parts list and 3D print files.
TL;DR
- PhoneBot comes out of Dennis Hong's lab at UCLA and treats a used smartphone as the whole robot brain, not a remote.
- The phone's camera and motion sensors supply vision and balance, and the walking AI runs on the device with no outside computer described.
- The AI was trained in simulation first, and early versions walked with a limp before the team moved to real hardware.
- The robot can get back up on its own after being laid flat on its face.
- The phone runs about $50 to $80, the body about $400, versus roughly $3,500 to $14,000 for comparable research humanoids.
- The parts list and 3D print files are being open-sourced, though the robot is tiny and has no arms yet.
How does an old smartphone work as a robot's brain?
A modern phone already packs most of what a small robot needs into one cheap, mass-produced package. It has a camera, motion sensors, a processor capable of running neural networks, a battery, and wireless connectivity. Researchers usually buy and wire these pieces separately. PhoneBot's pitch is that you can skip that step by reusing hardware people already throw into drawers.
In PhoneBot, each part of the phone maps to a robot function:
| Phone component | Robot role |
|---|---|
| Camera | Eyes, used for seeing the environment and following a person |
| Motion sensors | Balance and sense of body orientation |
| Processor | Runs the walking AI on the device |
The body supplies the legs and the structure. The phone supplies the intelligence. That split is why the phone price and the body price are quoted separately.
How was PhoneBot's walking AI trained?
The team trained the walking policy in simulation before putting it on a real phone. This is a common approach in legged robotics. A simulated robot can fall thousands of times at no cost, and learning happens far faster than it would on physical hardware.
Simulation is not perfect, though. The early versions of PhoneBot's AI walked with a limp, which shows the gap between a simulated body and a real one. Real motors, real friction, and real sensor noise all behave differently from their virtual versions. After the team iterated, the policy was loaded onto an actual phone, and the robot was shown walking around a living room.
The sources do not specify the training method, the model size, or the phone models used, so those details are best left to the lab's own release.
Can PhoneBot recover from a fall?
Yes. In the demonstration, the robot was laid flat on its face and got back up by itself. For a low-cost walker, that matters more than it sounds.
Cheap robots fall constantly. If a person has to pick the robot up after every stumble, it is hard to run long experiments or use it anywhere outside a controlled setting. Self-righting lets the robot keep going, and it makes the platform more practical for students and hobbyists who cannot babysit a prototype.
The motion sensors are the likely enabler here, since the robot needs to know which way it is oriented before it can decide how to move. The sources only confirm the behavior, not the exact mechanism.
How much does PhoneBot cost compared with research humanoids?
Cost is the headline. The numbers from the demonstration are:
| Item | Approximate cost |
|---|---|
| Used smartphone (the brain) | $50 to $80 |
| PhoneBot body | About $400 |
| Comparable research humanoids | $3,500 to $14,000 |
Adding the phone and body puts a full PhoneBot somewhere around $450 to $480, assuming you source a used phone at the quoted price. That is a fraction of the low end of the research humanoid range and a small share of the high end. These figures are rough, and they do not include tools, printing time, or any parts not listed in the lab's release.
The comparison also has limits. The research humanoids in that price range are not the same machines. PhoneBot is tiny and has no arms. It trades capability for accessibility.
What can PhoneBot do right now?
Today, PhoneBot walks, recovers from falls, and can follow a person around while filming them. That follow-and-film behavior comes straight from using the phone's camera as the robot's eyes.
What it cannot do yet is manipulate objects. It has no arms. It is small, and the demonstrated tasks are locomotion and tracking. Treat it as a platform for research and learning rather than a general-purpose helper.
Is PhoneBot really open source?
According to the demonstration, the team is releasing the parts list and the 3D print files, "everything" as the creator put it. That means someone with a 3D printer, a used phone, and the listed components should be able to build one. The exact license, repository location, and whether the training code and simulation setup are included were not stated in the sources. Check the lab's official release before planning a build.
Why does a phone-as-brain design matter?
Three practical reasons stand out:
- Low barrier to entry. A $50 to $80 brain and a $400 body put legged robotics within reach of classrooms, clubs, and individual builders.
- Reuse of existing hardware. Old phones are abundant. Turning them into robots gives that hardware a second job.
- Integrated sensing and compute. One device covers vision, balance, and inference, which simplifies the build.
The tradeoff is that a phone is not designed to drive motors or survive repeated falls, so the body has to handle that interface and protect the electronics.
Frequently Asked Questions
Who built PhoneBot?
PhoneBot comes from the robotics lab of Dennis Hong at UCLA. The sources identify the lab but do not list individual team members or a paper.
Does the phone just act as a remote control?
No. The phone is the robot's brain. Its camera provides vision, its motion sensors provide balance, and the walking AI runs directly on the phone rather than on a separate computer.
How much does it cost to build one?
The phone runs roughly $50 to $80 used, and the body is about $400. Together that is around $450 to $480, based on the quoted figures. Actual cost depends on your printer access, parts sourcing, and which phone you use.
Can PhoneBot pick things up?
Not yet. The current version is tiny and has no arms. It can walk, get up after a fall, and follow a person while filming.
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