Hello friend
If you have been following the progress of robotics over the decade you might have noticed something interesting: quadruped robots reached really good performance in the real world much earlier and more reliably than humanoid robots.
Quadruped robots like Boston Dynamics Spot, ANYbotics ANYmal, Unitree Go2 and others became useful in the world years before humanoid robots like Optimus or Figure 01 reached similar performance. Why did this happen?
The answer is in biomechanics, stability and the challenges of bipedalism.
1. Stability: The Big Difference
The obvious advantage quadruped robots have is that they are stable when they stand still.
- A quadruped robot can stand still with a stable base.
- Even if three legs are on the ground it can still balance.
- It can stay in one place without moving.
In contrast a humanoid robot has a small base when it stands on one foot. It has to be very careful with its balance all the time. It will fall. This means humanoid robots have to use stability. They have to keep moving to stop themselves from falling.
This one difference makes *quadruped robots much easier to control.
2. Biomechanics and Center of Mass
Quadruped robots have some advantages:
- They have a lower center of mass which means most of their weight is closer to the ground. This makes them more stable.
- They have support so if one leg fails or slips the other three can help.
- They can use their spine and tail to balance and manage their momentum.
Humanoid robots on the hand have a high center of mass and only two legs. This makes every step a balance. It’s like they are always falling and then recovering.
3. Locomotion and Energy Efficiency
Quadruped robots can use ways of moving like walking that don’t need much balance control. They can also use energetic ways of moving like trotting or galloping when they need to.
Humanoid robots have to use ways of moving right away. Every step needs planning, momentum management and balance control. This makes it harder to control them. Uses more energy.
4. Control Complexity
Controlling a quadruped robot is simpler because:
- Each leg can move more independently.
- The quadruped robot doesn’t need to adjust its body to balance.
- It’s easier to place the feet.
Humanoid robots need whole-body control. Moving an arm affects balance turning the head changes the center of mass slightly and every motion must be coordinated with the legs.
5. Real-World Performance
Quadruped robots can recover from mistakes easily. If a *quadruped robot slips on one leg the other three can keep it upright. If a humanoid robot slips on one foot it has to react quickly to stop itself from falling.
This is why quadruped robots were used in the real world first for things like inspection, logistics and working in difficult environments. Humanoid robots are now getting to the same level of performance.
Why We Still Build Humanoid Robots
though humanoid robots are harder to build we still work on them because they have some unique advantages:
- They can use the same tools and spaces as humans.
- They can manipulate things in spaces better.
- They are more accepted by people. Can interact with them more naturally.
- They could be very useful in roles that are meant for humans.
My Personal Opinion
Quadruped robots taught us how to build legged robots. They were like the “training wheels” for the robotics community. The great progress we’ve seen in robots over the last 10-15 years has given us valuable lessons in dynamics, contact mechanics, control and sim-to-real transfer. All of which are now helping us develop humanoid robots.
Humanoid robots are harder to build. Much harder.. That’s exactly why they’re so valuable. Solving the challenge forces us to push the boundaries of control, materials, energy efficiency and intelligence.
It’s really great to see humanoid robots getting closer, to the performance of robots from just a few years ago.