Why can some humanoid robots walk lightly, while others walk heavily?
What are the secrets of lightweight materials that enable robots to move from the laboratory to our lives?
Lightweighting is not simply about reducing weight; it’s about finding a balance between making robots more agile and having longer battery life, and it’s also a crucial hurdle for the industry to take off.
01 | Lightweight
1. How can reducing the weight by one kilogram increase a robot’s battery life by 30%?
The battery life and weight of a humanoid robot are directly related.
It’s not a simple addition or subtraction; it’s more like a car being able to travel a much longer distance with less luggage.
The robot’s joint motors need to move the entire body. For every bit of weight added, the motors need to consume more electricity to support the weight.
According to some data, with the same battery capacity, a device that is one kilogram lighter can have its battery life increased by nearly 30%.
This is because with a lighter motor load, not only does it consume less power and generate less heat, but it also uses less energy.
Just like a person carrying a heavy backpack gets tired easily, but unloading the burden allows them to go further and more easily.
2. How can seemingly ordinary materials withstand the extreme movements of robots?
Many lightweight materials may seem insignificant, such as commonly used aluminum alloys, but they can withstand repeated twisting and impacts to robot joints.
The mechanical properties of the material are at play here.
These materials not only need to be lightweight but also have sufficient strength and toughness, just like an athlete’s muscles, which need to be both flexible and powerful.
The aluminum alloy used for the leg bones has undergone special treatment, which greatly improves its fatigue resistance and enables it to withstand the maximum load during robot movement.
What’s even more interesting is that some composite materials can have their composition ratios adjusted to find the perfect balance between hardness and softness, adapting to the needs of different parts.
3. Why can’t lightweight materials be used interchangeably in different parts?
The material requirements for different parts of a humanoid robot vary greatly, so it is difficult to use the same materials interchangeably.
The head needs to be fitted with sensors, so the material must not only be lightweight but also not interfere with the signal, so engineering plastics are commonly used; the legs need to bear weight and resist impact, so high-strength aluminum alloy or carbon fiber composite materials are selected.
To make your hands soft enough to grip things, you need to use flexible polymer materials.
Just like different parts of the human body have different bones and muscles, each doing its own job.
If you use high-strength materials for the legs on the hands, the hands will become stiff and unable to operate flexibly; if you use plastic for the head on the legs, it won’t be able to support the entire body.
02 | Aluminum Alloy
1. Logic Preparation
Aluminum alloys are the basic material for lightweighting humanoid robots, and the key to their preparation lies in precision melting and modification.
During smelting, temperature and impurities must be strictly controlled. Too high a temperature will reduce the material’s properties, and too many impurities will affect its strength.
Companies often use vacuum melting technology to reduce the amount of impurities from the air that gets mixed in.
The subsequent modification process is even more crucial. Adding small amounts of elements such as magnesium and silicon can double the strength of aluminum alloys while maintaining their lightweight characteristics.
Lizhong Group uses this process to produce ultra-high-strength cast aluminum alloys that can just meet the stringent requirements of robot leg joints.
2. Vacuum high-pressure casting
Vacuum high-pressure casting is the core processing method for aluminum alloy parts.
This process involves injecting molten aluminum alloy into a mold under high pressure in a vacuum environment, which reduces porosity and defects inside the casting, making the parts denser and stronger.
The robot leg bone parts made by CITIC Dicastal using this technology are not only 15% lighter, but also 50 times more efficient in manufacturing and 60% cheaper.
This process is particularly suitable for mass production of high-precision aluminum alloy structural components, such as leg bones and joint shells.
The subsequent precision machining is also very important. CNC equipment is used to control the dimensions, and the error cannot exceed a few micrometers to ensure that the joints move smoothly.
3. Leg load-bearing
In component assembly, aluminum alloys are mainly responsible for the load-bearing structure of the components.
Legs support the entire body and are where aluminum alloys are most commonly used. Ultra-high-strength aluminum alloys are typically used for the skeleton and joint shells.
During assembly, it must be precisely matched with components such as motors and gears, and the overall weight must be controlled.
The limb structure solution provided by Lizhong Group to Weijing Intelligent uses aluminum alloy as the core component of the leg. By optimizing the structural design and assembly process, it achieves lightweighting while ensuring load-bearing capacity.
In addition, aluminum alloys are also used in parts such as arms and are combined with other materials to balance flexibility and strength.
4. Fatigue resistance and precision
The inspection of aluminum alloy components focuses on two aspects: mechanical properties and dimensional accuracy.
Mechanical performance testing includes tensile strength, fatigue resistance, etc., especially for aluminum alloy components in the legs, which must be able to withstand the maximum load during exercise.
CITIC Dicastal conducts rigorous fatigue tests on the aluminum alloy parts it produces to ensure they will not break down over a long period of time.
A coordinate measuring machine is used to inspect the shape and size errors of components to ensure dimensional accuracy.
Each aluminum alloy part must pass these two tests before it can proceed to the next step of assembly, in order to avoid affecting the robot’s motion performance.
5. Home and industrial scenarios
Aluminum alloys are suitable for different scenarios with distinct differences.
Home service robots are cost-sensitive and will choose conventional high-strength aluminum alloys that offer good value for money, balancing lightness and affordability; industrial robots, which require higher load-bearing capacity and wear resistance, will use specially modified ultra-high-strength aluminum alloys.
Regardless of the scenario, aluminum alloys can become the main material for limb structures due to their mature processes and stable performance.
Lizhong Group will provide different aluminum alloy materials and parts solutions according to the different needs of different manufacturers.
03 | Carbon fiber composite materials
1. Raw silk
The preparation of carbon fiber composite materials involves two steps: first, making the precursor fibers, and then compounding them.
The raw yarn is the foundation, made from acrylic or viscose fiber as raw material, and produced by high-temperature oxidation and carbonization, with a carbon content of over 90%.
The temperature control during this process is extremely strict; a difference of tens of degrees can affect the strength and toughness.
The subsequent composite molding process combines carbon fiber and resin and other materials to create a lightweight and strong composite material.
Guoneng Group combines carbon fiber and PEEK materials to create components that make robots more than 30% lighter and also improve their load-bearing capacity.
2. 3D printing + integrated molding
The core advantages of carbon fiber composite material molding and processing, 3D printing, and one-piece molding are its core strengths.
For complex parts with special shapes, such as joints and sensor brackets, traditional machining is difficult, but 3D printing can easily complete them.
In particular, printing with carbon fiber reinforced PEEK material can take advantage of the material’s lightweight and strong characteristics, and can also create customized complex structures.
Research from Hangzhou Dianzi University shows that 3D-printed carbon fiber composite components can meet the load and transmission requirements of robot joints.
Integrated molding can combine multiple parts into one, reducing connecting parts and further reducing weight.
3. High-load components
Carbon fiber composite materials are mainly used in critical components of robots that bear high loads, such as leg joints and chassis frames.
These parts need to be lightweight yet able to withstand heavy loads and impacts.
During assembly, the connection between carbon fiber composite materials and metal parts needs to be addressed. Special glue or mechanical connections are usually used to ensure a strong bond without adding weight.
Guoneng’s robot composite skeleton is made of carbon fiber composite material. Through integrated design, it is more than 30% lighter while ensuring strength.
4. Ultimate strength
The testing of carbon fiber composite components focuses on rigorous testing of strength and durability.
Because it is used in high-load applications, it is necessary to test indicators such as tensile strength, flexural strength, and impact resistance.
During testing, the sample is subjected to maximum load using specialized equipment to observe deformation and fracture.
Long-term durability tests are also required, simulating the long-term movement of a robot to check whether the material will suffer fatigue damage.
Only components that pass these rigorous tests can be used in the core structure of the robot.
5. High-end scenarios
Carbon fiber composite materials are relatively expensive and are mainly used in high-end humanoid robot applications.
For example, scientific research robots and heavy-duty industrial robots have extremely high requirements for lightness and load-bearing capacity, and are willing to bear higher costs.
When Tesla Optimus Gen2 was iterated, it used carbon fiber composite components, achieving the effect of being 10 kg lighter and increasing walking speed by 30%.
With the maturation of technology and the reduction of costs, it is expected to be used in mid-to-high-end home service robots in the future.
04 | Engineering Plastics
1. Polymerization reaction
The core of engineering plastics preparation is a precise polymerization reaction, and different types of engineering plastics have different reaction requirements.
Taking conventional engineering plastics as an example, by controlling the reaction temperature, pressure, and catalyst, the monomers are polymerized into polymer materials, and then modified, and filled or reinforced with fibers, they can have wear-resistant and temperature-resistant properties.
Kingfa Science & Technology produces ultra-high temperature resistant PPA materials in this way, which are already being used in common robot sensor brackets, joint shells, and other components, and are being supplied in batches.
2. Precision injection molding
The molding and processing of engineering plastics mainly uses two methods: precision injection molding and 3D printing.
Precision injection molding is suitable for mass production of simple structural parts, such as sensor brackets and decorative housings, ensuring dimensional accuracy and surface quality.
3D printing is suitable for customized complex parts, such as specially shaped joint liners and flexible gripping parts.
Regardless of the method used, it is essential to control the processing temperature and cooling rate to prevent a decline in material properties.
3. Signal-friendly materials
In component assembly, engineering plastics mainly serve the functions of signal compatibility and flexible adaptation.
The standard sensor bracket for the head is usually made of engineering plastic because it does not interfere with electromagnetic signals and can ensure that the sensor can detect signals normally.
The flexible gripping components of the hand are also made of flexible engineering plastic, enabling a soft grip without damaging the object.
During assembly, it is necessary to solve the connection problem between engineering plastics and materials such as metals and carbon fibers, while controlling the weight.
When Everbright Tongchuang and Dilos Intelligent collaborated, they specifically optimized the assembly technology of engineering plastics and other materials.
4. Temperature and wear-resistant
The testing of engineering plastic components focuses on temperature resistance, abrasion resistance, and dimensional stability.
When a robot is running, components such as motors will generate heat, and engineering plastic parts must be able to withstand certain high temperatures without deformation; plastic parts at the joints must have good wear resistance due to long-term friction.
During testing, the sample is aged in a high-temperature environment or subjected to long-term friction testing to check for changes in performance.
We also need to test dimensional stability to ensure that the parts do not deform under different environments, which would affect the precision of the parts fitting together.
05 | Magnesium Alloy
1. Inert gases
Magnesium alloys are lighter than aluminum alloys, and the challenges in their preparation lie in smelting, purification, and forming.
Magnesium is chemically reactive and easily oxidizes and burns during smelting, so the process must be carried out under the protection of an inert gas.
Purification requires the removal of impurities such as iron and silicon; otherwise, the material’s performance will be severely affected.
Nowadays, many companies use electro-vacuum melting technology, which can prevent oxidation and improve the purification effect.
After smelting, it needs to be modified by adding alloying elements to increase its strength.
Companies such as CITIC Dicastal are increasing their R&D efforts in magnesium alloy preparation processes to improve the stability of material properties.
2. Die casting
Magnesium alloys are mainly formed and processed using die casting, where molten magnesium alloy is poured into a mold and rapidly cooled to form the final shape.
This process is suitable for the mass production of complex magnesium alloy parts, such as small joint shells and internal support structures for robots.
During die casting, temperature and pressure must be carefully controlled to avoid defects such as porosity and shrinkage cavities.
After molding, it still needs to be precision-machined to correct dimensional errors and ensure a precise fit with other components.
Currently, the cost of magnesium alloy die casting is still relatively high, which is one of the key factors restricting its large-scale application.
3. Corrosion resistance and precision
The key to inspecting magnesium alloy components is to control both corrosion resistance and mechanical properties.
Magnesium has poor corrosion resistance and is prone to rusting. It is necessary to test the corrosion under different environments to verify the effectiveness of the surface treatment process.
Mechanical properties must be tested for tensile strength, flexural strength, and fatigue resistance to ensure that the components meet the requirements for use.
During testing, samples are placed in humid or salt spray environments for corrosion testing or subjected to long-term fatigue testing to check for changes in performance.
Only magnesium alloy components that pass rigorous testing can be used in practical applications.
06 | PEEK Material
1. High-temperature polymerization
The synthesis of PEEK materials mainly follows a nucleophilic substitution route, using 4,4-difluorobenzophenone and hydroquinone as raw materials, and polycondensing at around 320°C under nitrogen protection with diphenyl sulfone as a solvent.
This process has high technical barriers. First, the molecular weight and distribution must be precisely controlled because the reactants are volatile at high temperatures and will be lost with the gas, making it difficult to control the proportion of monomers participating in the reaction. Second, temperature control is difficult. The high temperature of 330℃ places strict requirements on the material of the reactor, and it is even more difficult to ensure the temperature uniformity inside a large reactor.
It is also necessary to strictly control impurities and gel formation and stabilize the product color, as any deviation in any step will affect performance.
Currently, global production capacity is concentrated in companies such as Vigus in the UK and Synesqo in Belgium, while domestic companies are still breaking through the technological bottlenecks of mass production.
2. Carbon fiber composite properties
Pure PEEK material has good performance, but it is brittle and easily cracks when subjected to external impact. Combining it with carbon fiber to form CF/PEEK material can perfectly solve this problem.
The high strength and high modulus of carbon fiber allow the composite material to retain the advantages of PEEK, such as high temperature resistance and corrosion resistance, while significantly improving its strength and resistance to deformation.
For example, PEEK material reinforced with 30% carbon fiber has a modulus of 15 GPa and a density of only 50% that of aluminum alloy. When used in harmonic reducers, it can increase the load-bearing capacity by more than 30% and also solve the resonance problem of metal materials.
Domestic companies such as Guangwei Composites have developed composite products, such as PEEK prepreg yarn, and are currently promoting the construction of pilot production lines.
3. Extreme environments and precision performance
Testing of PEEK materials focuses on their adaptability to extreme environments and precision performance.
The high temperature resistance test verifies the strength stability at 260℃ for 5000 hours to ensure long-term high-load operation without failure; the wear resistance test controls the gear wear rate to be below 0.01 mm/1000 hours to ensure precise and long-lasting joint transmission.
For CF/PEEK materials, tensile strength, flexural modulus, and other indicators must also be measured to ensure that the strength is comparable to that of titanium alloys, while the density is only 36% of that of titanium alloys.
In practical application verification, extreme working conditions such as a robot falling from a height and temperatures ranging from -40°C to 220°C are also simulated to test the impact resistance and temperature adaptability of the components.
