Heat Dissipation, Integration, And Cost Challenges for Robot Frameless Torque Motors

In the surging wave of humanoid robotics, frameless torque motors have become the core choice for joint actuation, thanks to their compact size, high power density, and high torque at low speeds. Unlike conventional motors, frameless torque motors dispense with the housing, bearings, and base, retaining only the stator and rotor as their two main components, allowing them to be directly embedded into the overall system. However, this “houseless” design, while offering great flexibility for high integration, also gives rise to three major pain points—heat dissipation, integration, and cost—which have become critical bottlenecks limiting the large-scale commercialization of humanoid robots.

Pain Point 1: Heat Dissipation – High Temperature Is the “Invisible Killer” of Motors

The heat dissipation issue of frameless torque motors stems from their inherent structural characteristics. Lacking an independent housing and fan, the heat generated by the motor cannot be quickly dissipated through housing-based air cooling as in traditional motors. When the robot works continuously, the motor generates significant heat. Prolonged exposure to high temperatures accelerates aging of winding insulation, degrades bearing lubrication, leads to frequent motor faults, and severely undermines operational stability.

Even more severe are burst heat scenarios. When the robot executes high-dynamic motion commands, the instantaneous current surges, and the cooling system often cannot remove the heat quickly enough, causing the internal temperature to spike. Once the temperature exceeds the motor’s thermal limit, it can easily cause winding short circuits, insulation damage, or even motor burnout and robot loss of control. Academic studies have also pointed out that temperature rise caused by Joule heating and eddy-current effects is a major challenge in the application of frameless torque motors.

To address this pain point, the industry is making breakthroughs from two angles: materials and processes. Magnetic circuit optimization reduces heat generation at the source—by improving magnetic field design, using high-grade neodymium-iron-boron (NdFeB) materials and low-loss magnetic conductors, hysteresis losses, eddy-current losses, and copper losses can be significantly reduced. Through magnetic circuit optimization, overall losses are cut by 20%, while torque is increased by 10% under the same input current. Potting technology makes a breakthrough on the heat-dissipation path—vacuum potting fills the internal gaps of the motor with ultra-high-thermal-conductivity potting compound, efficiently conducting heat from the heat source to the external cooling structure. In addition, directly “soldering” the stator windings to the joint’s metal housing via thermally conductive media, and using housing fins or built-in liquid-cooling channels to expel heat, has also become an effective means to improve continuous output capability.

Pain Point 2: Integration – “Making the Most of a Tiny Space”

The “houseless” design of frameless torque motors was originally intended to enable high integration, but integration itself has become a new challenge. The joint space in robots is extremely limited, requiring high torque density output within a very small volume, while also accommodating harmonic reducers, brakes, sensors, drivers, and many other components.

The integration challenge is first evident in cabling. The cramped internal space of the joint makes it impossible for traditional solid-shaft motors to route cables internally; cables must be routed externally, taking up space and compromising aesthetics and reliability. To address this, the industry has introduced large-hollow-shaft designs—reserving a through-hole in the motor center so that power cables, signal lines, and even fluid pipes can pass through the motor interior.

Another challenge is assembly precision. Since frameless motors lack a housing as a positioning reference, the stator and rotor must be directly embedded into the robot structure, imposing micron-level requirements on assembly concentricity and coaxiality. The traditional “eye + hand” assembly approach is no longer sufficient. Furthermore, while new technologies such as axial-flux motors offer higher power density, their system-integration maturity on robotic platforms is still lacking, and the industry supply-chain capabilities remain to be strengthened.

The industry is lowering the integration barrier through standardization and modularization. Standardized mechanical interfaces and plug-and-play drive modules are helping customers reduce integration complexity. At the same time, integrated joint modules that pre-assemble the motor, reducer, sensors, and other components allow robot manufacturers to purchase complete modules rather than assembling them in-house.

Pain Point 3: Cost – The “Hefty Price” of High Performance

Cost is the most tangible hurdle standing in the way of widespread adoption of frameless torque motors. Currently, a single frameless torque motor costs over RMB 2,000, accounting for 15% of the total robot cost. With about 30 joints in a humanoid robot, motor costs alone exceed RMB 60,000, not including drivers and ancillary components.

The high cost stems from multiple factors. Material costs—high-performance NdFeB permanent magnets are the core of the motor, and their rare-earth composition and grain-boundary diffusion processes directly determine torque density, but fluctuations in the rare-earth supply chain often keep prices high. Manufacturing processes—the winding, potting, and assembly steps of frameless motors require extremely high precision, and traditional production methods rely heavily on manual labor, leading to inconsistent cycle times and yield fluctuations, further driving up unit costs.

Cost-reduction pathways are being pursued in several directions simultaneously. Process improvement is the most direct path—by optimizing rotor manufacturing processes and adopting large-ratio hollow-shaft designs, costs have been effectively reduced; products have seen a 30% reduction in volume and a 20% increase in torque, with performance on par with international brands. Automated production lines are the key to cost reduction at scale—fully automatic intelligent lines achieve an output of “one motor wound per minute” with a yield of 98.6%, completely breaking the efficiency bottleneck of traditional manual methods. High-precision automated equipment and intelligent inspection systems ensure consistent performance parameters for every motor. Material innovation is also advancing—heavy-rare-earth reduction technologies have lowered the cost share of rare-earth magnetic materials to 18%; integrated die-casting processes have cut production costs by 18%.

Conclusion

Heat dissipation, integration, and cost constitute the three checkpoints on the road from laboratory to mass production for frameless torque motors. Dissipation affects reliability, integration determines feasibility, and cost impacts commercial viability—they are interwoven, and any weakness in one link drags down the entire process. Fortunately, the industry is systematically tackling these challenges from multiple dimensions, including magnetic circuit optimization, potting processes, hollow-shaft design, and automated production lines. In the future, with the application of new materials such as embedded micro-channel cooling and amorphous alloy cores, and as large-scale production continues to advance, frameless torque motors are expected to truly become the “reliable core” that drives humanoid robots into every household.