Bridging the divide between deterministic physics-based control and policy-driven adaptation, Boston Dynamics released a video today showing its Atlas humanoid using wheels to move around. The “experiment” combined classical model-based motor control with whole-body reinforcement learning to maintain dynamic stability across unstructured, real-world terrain.
In the video, Andy Wu, controls engineer for Atlas at Boston Dynamics, highlights some recent experiments that he executed by attaching wheels to Atlas’ legs. Boston Dynamics said “a wheeled Atlas isn’t a product. It’s a research testbed.” Wu’s intention was to push the actuation to its limits.
Another goal of the experiment was to understand unstructured environment adaptability. Wu addresses the limitations of purely model-based control when navigating unpredictable, real-world conditions that are difficult to model or simulate.
Through a whole-body reinforcement learning (RL) policy, Atlas demonstrates that it can process real-time proprioceptive feedback and velocity commands. The experiment also outputs dynamic pose and force adjustments to mitigate unmodeled disturbances and non-ideal contact states.
Boston Dynamics attached wheels to the feet of the Atlas humanoid for a set of controls engineering experiments. | Credit: Boston Dynamics
Atlas moves like a skater
In addition to learning how to move with wheels for feet, Atlas also performs pirouettes and various aggressive actuation maneuvers.
This demonstrates that Atlas can smoothly switch between fast rolling on flat terrain and articulated legged motion over obstacles or irregular surfaces.
Wu trained the system in sim. The system learned all of the behaviors in sim and executed them in real life, with surprising accuracy, according to Wu.
Wu said converting Atlas’ locomotion style was “wonderfully simple.” A single custom adapter mounts an off-the-shelf scooter rim onto Atlas’ existing ankle actuator, and that’s the only new part in the whole build. Because Atlas was designed from the start to be produced at high volume and to be easy to service, Wu said the retrofit was about as involved as swapping a wheel on a bicycle.
The software side was just as straightforward, he said. Each wheel is modeled as an “ankle” that can spin continuously, so all Wu had to do was take the baseline robot model and swap the feet out for wheels.
Real-world implications for humanoid operation
The next question that Wu intends to answer is the policy response to failed actuators. This is key to safety and to understanding how the system will respond to a system failure.
The primary takeaway for Wu and the controls engineering team at Boston Dynamics is to understand control synergy. The video demonstrates that merging classical motor controls (for baseline stability) with whole-body RL (for reactive adaptation) yields superior real-world agility compared to using either method alone.
Wheels vs. legs debate continues
Boston Dynamics’ latest Atlas experiment adds another interesting data point to the ongoing wheels-versus-legs debate in humanoid robotics. While many companies are developing wheeled humanoids, others are committed to legs for navigating environments designed for people.
Agility Robotics recently said it is also exploring wheeled robots as part of a broader family of human-centric, multipurpose platforms. Co-founder and Chief Robot Officer Jonathan Hurst said Digit likely won’t get wheels, but the company is exploring other wheeled configurations.
Again, Boston Dynamics said a wheeled Atlas is a research testbed, not a product. Still, experiments like this raise an interesting question about how much of the humanoid form factor needs to be human-like to be commercially useful. We’ll be watching to see where the industry goes next.
The experiments come as Boston Dynamics prepares to ramp up Atlas testing at Hyundai facilities and continues developing the humanoid’s capabilities, including its new four-fingered gripper. The Robot Report will be watching how these developments translate into real-world deployments.
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