Walking, when you really think about it, is controlled falling. We lean forward, but before it gets too dangerous and we lose our balance, our legs stop us from falling. Science fiction author Douglas Adams would have loved this, because in his satirical book The Hitchhiker’s Guide to the Galaxy, one of the protagonists explains how to learn to fly:
“The Guide says there is an art to flying”, said Ford, “or rather a knack. The knack lies in learning how to throw yourself at the ground and miss. … Clearly, it is the second part, the missing, which presents the difficulties.”
Marvin, the paranoid android from this science fiction series, never really thinks about whether walking might be a controlled fall or something else—his own problems keep him too preoccupied. But humanoid robots—or, more accurately, the manufacturers of humanoid robots—must ask themselves this question. In the list I compiled of more than 200 companies that are developing a total of around 300 humanoid robot models, a clear division stands out. On the one hand, there are humanoids that move on wheels, and on the other, those that fall in a controlled manner on two legs.
The list also shows that about 40 percent of humanoids have a wheeled platform, while the rest rely on two legs. Some manufacturers offer their robots with both wheels and legs, leaving the choice up to the customer. But how should one decide? Which option is better?
First, there is the question of where the humanoid robot will be operating. Will it move on flat surfaces without unevenness, thresholds, or obstacles? Will it need to navigate steps or thresholds? Are there bottlenecks such as narrow doors, or can obstructions from parked or moving objects in tight spaces or hallways be expected on a regular basis? Is the robot’s speed of movement a factor? Do vibrations or shaking caused by the robot’s movement affect the cargo it is carrying? Is the noise level generated by the humanoid a concern? What are the robot’s range and energy consumption? Where will the robot be deployed, and in which processes will it be integrated with humans? How does the choice between wheels and legs affect the robot’s stability? How complex and maintenance-intensive is the robot?
A clear advantage of a wheeled platform is its stability. No algorithms or processor time are required to continuously stabilize the robot. Even in the event of a power outage, the robot simply comes to a stop and does not tip over. It can also move much faster on flat surfaces without jostling its payload too much. Its movement is quieter; only the sound of rolling can be heard. In contrast, robots with legs often produce a lot of mechanical and hydraulic noise, as well as the sounds generated when their feet touch the ground.
Bipedal robots offer other advantages. For one thing, they can navigate almost any terrain, no matter how flat it is or how many obstacles are present. They can climb steps and even ladders, jump over obstacles, and do somersaults. Their legs also allow them to pass through or climb over narrow gaps on the ground. This makes them more versatile and not limited by the terrain. However, there are some drawbacks to having two legs. They are more expensive and require more maintenance because they have more mechanical components. Stabilizing the robot is a challenge, especially during sudden stops, malfunctions, or power loss. A 60-kilogram robot cannot simply fall over and endanger people. In addition, they consume more energy and are noisier.
I have summarized the pros and cons of the two platforms in the following list
| Requirement | Wheels | Legs |
| Flat Plain | very well suited | very well suited |
| Unevenness | not well suited | very well suited |
| Bottlenecks | It usually can’t be passed | can weave through or climb over it |
| Stairs | barely to impossible | very well suited |
| Stabilization | simply | complex |
| Processor Power for Stabilization | low | high |
| Stabilization During a Power Outage | simple | Safety measures are required |
| Speed | slow to fast | slow to moderate |
| Shaking | low | hoch |
| Noise Level | low | moderate to high |
| Energy Consumption | low | moderate to high |
| Range | hoch | medium to low |
| Mechanical Complexity | low | hoch |
| Maintenance | simply | time-consuming |
| Integration into Workflows Involving People | limited | almost unlimited |
| Applications | limited | almost unlimited |
This is an excerpt from my book Homo Syntheticus: How Humans and Machines Are Merging, published in German in 2026.Ho
