As humanoid robots approach mass production, heat dissipation increasingly resembles a &#34;hard threshold&#34;—it's not just about lowering the temperature; it directly affects how much torque the joints can output, whether the chips will experience thermal throttling, and if the batteries can safely fast charge. This report from Guohai Securities elevates thermal management from a &#34;supporting role&#34; to the forefront, dissecting where the heat in humanoid robots comes from, where it gets stuck, and how engineering might circumvent these issues.
Zhang Yuying, the chief analyst for machinery at Guohai Securities, wrote in the report, &#34;In the energy generated by the robot, 90% is directly converted into heat, accumulating in confined spaces such as motor windings, gearboxes, and chips,&#34; and in extremely compact structures like the joints of dexterous hands, &#34;the gap inside the cavity may be less than 2mm,&#34; making it impossible to fit traditional 5mm centrifugal fans.
The trouble with heat is not just &#34;burning.&#34; It can trigger thermal throttling in chips, leading to a &#34;snowball&#34; decline in efficiency; high temperatures can also reduce signal transmission stability, even pushing the robot's continuous operating capability to the edge of protection mode. The report dedicates considerable space to discussing copper losses, iron losses, and wind losses in joint motors, as well as the temperature constraints of drivers, reducers, and encoders, ultimately addressing the trade-offs between air cooling, liquid cooling, and chip control.
More notably, heat dissipation does not only occur at the joints. The battery and computing power stacked in the torso are also heat sources, with patents from Tesla and Figure AI focusing on &#34;how to route airflow, where to place air inlets and outlets, and how to share a cooling interface between the computer and the battery.&#34;
<h2>Low Energy Efficiency, Dexterous Hands as the Ultimate Test for Heat Dissipation</h2>
The report compares &#34;humanoid robots (estimated) vs. humans,&#34; concluding that at the same power level, robots have significantly lower energy conversion efficiency, making heat accumulation more likely in confined spaces. Once heat builds up, the first issues often arise not from the outer shell temperature but from the junction temperature of the chips and drive losses.
The report provides a typical positive feedback loop: once thermal throttling is triggered, the on-resistance RDS(ON) of the drive chip has a positive temperature characteristic; for every 10°C rise in junction temperature, its resistance increases by about 4%. The increased resistance further raises I²R losses, generating heat more quickly, and system efficiency subsequently declines in a &#34;snowball&#34; effect.
Two additional consequences are also highlighted: electromagnetic interference misalignment in high-heat environments and decreased signal transmission stability; as well as the robot's weak capability for sustained high-speed operation, frequently entering protection mode, directly suppressing its application potential.
Among these, the heat dissipation challenge is greatly amplified at the joints of dexterous hands: space is extremely limited, with the report noting that the gap inside the cavity may be less than 2mm. Traditional 5mm centrifugal fans cannot be physically installed—this means that the mature air cooling solutions used in industrial equipment fail here. Meanwhile, dexterous hands require high power density output, lightweight, and compact size, which are inherently conflicting requirements.
The motor layout of dexterous hands also affects heat dissipation. Current mainstream solutions are categorized into three types: built-in (motors placed within the palm or fingers), external (all drivers in the forearm), and hybrid. The report predicts that Tesla's next-generation dexterous hands may adopt a hybrid layout: wrist motors combined with palm motors, driven by tendon ropes
This structure moves the densely heated motor to the wrist area with more space, which also loosens the internal space of the fingers.
<h2>The essence of copper loss is &#34;triangular trade-off&#34;: volume, torque, and temperature rise must be considered together</h2>
The report breaks down the losses of joint motors in detail. In typical proportions, copper loss (stator winding) 40%-60%, iron loss (stator core, hysteresis + eddy current) 20%-30%, mechanical loss (bearings/gap) 5%-10%, permanent magnet loss (rotor permanent magnets) 5%-10%. The switching/conduction losses of power devices (such as MOSFETs) in the drive module can account for 30%-60% of the &#34;total drive loss.&#34;
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These losses ultimately fall on a set of &#34;temperature red lines&#34;: winding &lt;155°C; encoder &lt;100°C-120°C; the reducer may only be &lt;65°C (the report gives an example: if the rated temperature of the reducer is 65°C, and the nearby motor winding temperature is at most 15°C higher, then a maximum winding temperature of 80°C would completely limit the design space of the motor). Heat dissipation is not just about making the motor stronger; it is often locked in by neighbors such as reducers, feedback devices, and bearings.
The report's approach to copper loss resembles a combination of &#34;structure + materials + algorithms.&#34; Under high dynamic conditions, the compact module has insufficient heat dissipation area, leading to excessively high natural convection thermal resistance; the temperature gradient can also introduce asymmetric thermal deformation, resulting in multi-degree-of-freedom pose errors. Thus, the engineering problem becomes: how to coordinate the volume, torque, and heat of the motor.
The directions it provides include:
<blockquote>
<ul>
<li>Structure: Develop high heat dissipation structures and improve heat transfer efficiency. The report cites a patent for a flattened rotating joint module from XinJian Transmission as an example, using a &#34;parallel&#34; structure of the motor and reducer to alleviate thermal accumulation in compact structures.</li>
<li>Materials: For example, using low thermal expansion alloys to manufacture screws to reduce thermal deformation; the XinJian Transmission plan also mentions using high thermal conductivity carbon fiber composite materials for housing components.</li>
<li>Algorithms: Real-time temperature compensation to suppress temperature drift errors; heating-sensitive sensors to allow the control system to reduce current/speed/stop when necessary.</li>
</ul>
</blockquote>
<h2>Iron loss and rotor eddy currents: suppress harmonics first, then discuss heat sinks</h2>
In the iron loss section, the report focuses on rotor eddy current losses: the rotor of a high-speed permanent magnet motor is in a complex magnetic field environment, where the harmonic magnetic field rotates asynchronously relative to the rotor, inducing electromotive force in the conductive components of the rotor and forming eddy currents, leading to eddy current losses. It emphasizes a premise: if eddy current losses are underestimated, overheating of the rotor during actual operation can pose safety hazards, and cooling design can fundamentally go wrong.
The suppression approach is summarized into two lines:
<blockquote>
<ul>
<li>Suppress asynchronous magnetic fields from the source: the goal of spatial harmonics is to make the air gap magnetic field more sinusoidal; the goal of temporal harmonics is to make the phase current of the winding more sinusoidal. Methods include optimizing the stator tooth slot structure, optimizing winding forms, increasing the carrier ratio of power devices, adding filter reactors between the motor output and the controller, and improving stator inductance from the design perspective of the motor, but each method has its costs (such as volume weight, dynamic response, losses, and costs)</li>
<li>Shielding from the transmission path: Use a shielding layer to isolate alternating magnetic fields in positions such as the sheath; or cut the eddy current loop on the metal sheath by creating grooves/holes on the surface of the sheath.</li>
</ul>
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</blockquote>
<h2>Air Cooling is the Cheapest, Liquid Cooling is More Effective</h2>
The report does not label air cooling as an &#34;outdated solution,&#34; but rather emphasizes that it remains one of the economically reliable routes: Natural convection is suitable for devices with a heat flow density not exceeding 0.8 W/cm²; forced air cooling can achieve a cooling effect 5 to 10 times that of natural cooling. The problem is that air cooling is sensitive to ambient temperature, increasing airspeed can lead to noise, and the selection of fans and duct design can directly affect failure rates.
A more realistic bottleneck comes from the structure: the gap between the joints of the dexterous hand is less than 2mm, making it impossible to install traditional 5mm centrifugal fans. The report provides two cases focused on &#34;fitting&#34;:
<ul>
<li>UBTECH's joint structure patent: Simplifying the joint module structure, setting up a hollow structure, and installing cooling devices (such as cooling fans) on the outer wall of the casing for air cooling.</li>
<li>MEMS micro fans: With a thickness that can fit into spaces of &lt;1.5mm, they can be mounted on hotspots such as chips and motor drivers to generate micro-jets for localized cooling using piezoelectric drive; the report mentions that their heat flow density handling capability can exceed 100 W/cm².</li>
</ul>
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Compared to air cooling, circulating liquid cooling introduces cold plates, fluid circuits, pumps, and expansion tanks, making the structure more complex; however, the thermal conductivity and heat capacity of liquids are high, allowing for coverage of higher heat flow density scenarios. The report lists common liquid cooling methods such as circulating flow, immersion, and jet cooling.
In the &#34;oil cooling&#34; section, it cites the oil cooling solution of New Sword Transmission's planetary roller screw: By designing oil passages and oil holes, hydraulic oil forms a static pressure oil film on the meshing surface, reducing the friction coefficient and wear; hydraulic oil also carries away heat, reducing thermal deformation. This type of solution addresses both heat dissipation and lifespan, but also introduces engineering challenges such as sealing, circuits, and maintenance.
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Thermal management is not just a structural and fluid issue; there is also room at the chip level.
The report separately highlights &#34;chip control,&#34; with the core focus being: using better control to reduce the driving current, thereby naturally reducing heat. It cites Peak Technology as an example, mentioning that high-performance stepper motor control chips can enable stepper motors to transition from open-loop to closed-loop drive, achieving high reliability under smaller driving currents, alleviating power consumption and heating issues; it also mentions that its products cover main control chips MCU/ASIC, driver chips HVIC, power devices MOSFET, etc., with the FU75xx series MCU being used in control scenarios such as robotic joints and dexterous hands
<h2>Batteries and Computing Power in the Torso: Tesla and Figure Use Air Ducts to Bind Two Heat Sources Together</h2>
In the battery section, the report first presents a reality trade-off: there is a balance between &#34;standardization vs performance premium&#34; in the application path of robot batteries. It lists two industry trends:
<ul>
<li>LG Energy Solution: will launch a 2170 cylindrical cell product line for robots/drones at InterBattery 2026, with performance grading; among them, the H52A supports a maximum output of 8C ultra-high power, completing fast charging in about 15 minutes.</li>
<li>XPeng: will release the humanoid robot IRON in November 2025, emphasizing the application of all-solid-state batteries: weight reduced by 30%, energy increased by 30%, with a goal of mass production by the end of 2026.</li>
</ul>
On the patent level, the report uses patents from Tesla and Figure AI to illustrate the design trend of &#34;torso thermal management&#34;:
<ul>
<li>Tesla's solution revolves around forming a conduit path between the energy storage device shell and the computer system, using fans to drive airflow. The conduit is equipped with heat sinks for both the energy storage device and the computer, simultaneously dissipating heat from the battery and computer; it also describes that the robot can be configured with multiple fans/ventilation openings/heat sinks, with materials that can balance structural support and thermal management.</li>
<li>Figure AI's solution places the air intake and exhaust openings on the lower edge of the waist and the side of the arm tubes, with fans in the upper torso area drawing in fresh air, which is expelled from the lower torso/waist ventilation openings after heat exchange; airflow can be used to cool computing devices (GPU, CPU) during task execution, and during charging, it is used to cool the battery to shorten charging time and allow for larger currents. Its patent also provides a design range for battery capacity and endurance: the battery can be 1.5–5 kWh (preferably 2–3 kWh), with a range of 2.5–8 hours (preferably at least 3.5 hours)</li>
</ul>

The latest research report from Guohai Securities reveals that 90% of a robot's energy is directly converted into heat, and the gap between the joints of dexterous hands is less than 2mm, which is the limit for heat dissipation. Among them, air cooling is one of the economically reliable routes, with forced air cooling achieving 5 to 10 times the effectiveness of natural cooling. Circulating liquid cooling introduces cold plates, fluid circuits, pumps, and expansion tanks, making the structure more complex; however, the liquid's thermal conductivity and heat capacity are high, allowing it to cover scenarios with higher heat flux density

90% of energy is converted into waste heat! The heat dissipation problem of humanoid robots is a "fatal bottleneck" for commercialization