UCLA researchers developed PhoneBot, a small humanoid robot that uses an Android smartphone as its brain to walk on two legs. (Ruochen Hou et al./UCLA RoMeLa)
Got an old Android phone collecting dust in a drawer? You might want to hang on to it. Researchers at UCLA have figured out how to turn an aging smartphone into the brain of a small walking robot. It's called PhoneBot, and it can walk on two legs, follow people and even get back up after falling face down.
The most surprising part? The researchers estimate the robot's hardware costs about $400, excluding the phone. So, that forgotten smartphone could have a pretty interesting second life. Here's how the researchers pulled it off and what it would take to build one yourself.
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How UCLA turned an old Android phone into a walking robot
PhoneBot comes from UCLA's Robotics and Mechanisms Laboratory, also known as RoMeLa. The team built a miniature humanoid robot that stands about 19 inches tall and weighs roughly four pounds, including the smartphone attached to its body.
Instead of developing an expensive custom computer, researchers used technology already inside an Android phone. The robot has 13 motorized joints, with six in each leg and another that lets its upper body rotate. That extra movement allows the smartphone's camera to turn toward someone while the robot's feet stay planted.
A box filled with electronic waste and broken devices. (Getty Images)
The researchers’ goal is to make humanoid robotics more affordable for schools and research teams that cannot spend thousands of dollars on specialized machines.
Your old Android phone becomes the robot's brain
Think about everything your smartphone already does. It can recognize objects through its camera and detect movement using built-in sensors. It also has enough processing power to run sophisticated software. PhoneBot puts those capabilities to work. An Android app uses the phone's motion sensors to help the robot maintain its balance. Meanwhile, the camera helps it recognize and track people. The phone also runs an artificial intelligence-powered walking controller that tells the robot how to move. Those instructions travel over Wi-Fi to a small computer inside the robot, which communicates with the motors. The smartphone has no physical electrical connection to the robot's hardware. That design makes it easier to swap phones without rewiring the machine. Researchers trained PhoneBot's walking system in computer simulations before testing it on the actual robot. They also developed a way to improve how evenly it uses both legs. As a result, PhoneBot can walk on flat surfaces and stand up from a face-down position. For something powered largely by an old smartphone, that's quite an accomplishment.
Even a nearly 10-year-old Android phone can work
Here's something I found especially interesting. UCLA didn't need the latest expensive smartphone to make PhoneBot work. In fact, the researchers successfully tested its core functions on four different Android devices, including an Honor 9 released back in 2017. The other models included a Samsung Galaxy A16 5G and two Motorola Moto G phones from 2024 and 2025.
Researchers purchased the three prepaid models for roughly $50 to $90 each. Those were the prices reported during testing, rather than guaranteed prices today. All four phones handled the essential functions, including movement control and camera-based recognition. However, the older Honor 9 could not run one of the robot's mapping features because the required Google services were unavailable on that device in the United States. That means you cannot assume every Android phone will work. Still, the tests suggest you may not need an expensive new phone to run a capable little robot.
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UCLA's PhoneBot demonstrates its ability to walk, track a person using its smartphone camera and stand back up after falling face down. (Ruochen Hou et al./UCLA RoMeLa)
Can PhoneBot follow you around?
Yes, at least within the limits of what UCLA has demonstrated. PhoneBot can use its smartphone camera to identify a person and adjust its movement to follow them. It can also rotate its upper body to keep someone in view. The robot supports conversational interaction, too.
However, there's an important limitation. Its current system uses a separate laptop to process speech and generate AI responses. The smartphone records your voice and plays the response through its speaker. Before you start thinking about having PhoneBot clean your house, there's something else you should know. It doesn't have arms. That means it cannot pick up your laundry or carry groceries.
Researchers also trained its walking system on flat ground, so navigating stairs and uneven surfaces remains a challenge. For now, PhoneBot is best viewed as an experimental platform. UCLA has demonstrated what it can do under research conditions, but it hasn't established that the robot can independently navigate a typical home.
Could you build a walking robot with your own Android phone?
If you're comfortable with electronics and robotics, PhoneBot could become a pretty interesting project. UCLA has developed it as an open-source research platform and published hardware designs and building resources. The official PhoneBot website at phonebot.dev/ provides information about the robot's design, components and assembly process. The published hardware materials are available for noncommercial use under a Creative Commons license.
There's an important distinction, though, between having the hardware plans and being able to build a fully working robot. The project website provides hardware designs and assembly resources but does not clearly offer a download for the complete Android app and trained walking software. Although UCLA describes PhoneBot as an open-source platform, anyone hoping to reproduce its capabilities should first confirm that the necessary software is available.
And there's another consideration: the $400 price tag. It's an approximate hardware cost, and it doesn't include the smartphone. Depending on what equipment you already have, you may also need access to a 3D printer and tools for assembly. Shipping and other expenses could push the total higher. You'll also need the technical skills to put everything together and configure the software. So, don't expect to download an app and watch your old phone suddenly sprout legs. There's real engineering involved.
Why PhoneBot could make walking robots more affordable
Humanoid robots are getting a lot of attention, but building one remains expensive. Some small research models cost several thousand dollars. More advanced systems can cost considerably more. PhoneBot takes advantage of hardware that millions of people already own. By letting a smartphone handle much of the sensing and computing, researchers can avoid buying some specialized components. That helps bring the overall cost down.
The approach could also make robotics more accessible to students. Instead of requiring a large research budget, a smaller team could experiment with a relatively inexpensive walking machine. They could test new software or explore ways to improve movement without building every electronic component from scratch.
The UCLA team already has ideas for what comes next. Researchers want to improve PhoneBot's ability to handle uneven terrain and eventually give it lightweight arms. They're also exploring ways to run more conversational AI directly on the smartphone, which could reduce the need for a separate computer. Those improvements are still future goals. Even so, PhoneBot offers a promising starting point for building more affordable humanoid robots.
PhoneBot combines a smartphone with 13 motorized joints to create a walking robot that costs approximately $400 in hardware, excluding the phone. (Ruochen Hou et al./UCLA RoMeLa)
What this means to you
You probably won't see PhoneBot on store shelves anytime soon. But this research shows how much useful technology may still be inside a smartphone you've stopped using. A phone that feels outdated for daily use could still handle surprisingly demanding tasks.
If you're interested in robotics, PhoneBot could eventually offer a more affordable way to experiment with walking machines. Meanwhile, for families with kids who love technology, an accessible version of this project could make for a fascinating hands-on learning experience.
And if you've been thinking about getting rid of your old Android phone, this research offers another reason to consider what it might still be capable of. Of course, building a robot won't be for everyone. You can also sell, donate or recycle your old phone. Before you do, check out our article on securely getting rid of your old cell phone to make sure your personal information doesn't go along with it.
Kurt's key takeaways
I love the idea that a smartphone sitting forgotten in a drawer could become the brain of a walking robot. We've gotten so used to replacing our phones every few years that we sometimes overlook how powerful these devices still are. What UCLA has done with PhoneBot makes me wonder how many other uses we're missing. Now, let's be realistic. This little guy isn't ready to take over household chores, and putting one together requires some serious know-how. But the price is what caught my attention. When researchers can build a walking robot with roughly $400 in additional hardware, it opens the door to possibilities that once seemed out of reach. I'd love to see someone turn this into an affordable kit that families could build together. That could be a great way to get kids excited about engineering.
Would you spend a few hundred dollars to turn your old Android phone into a walking robot? Let us know by writing to us at CyberGuy.com.
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