Servo & Frameless Torque Motors

What a servo motor and a frameless motor are

A servo motor is a permanent-magnet motor that works inside a closed loop. As Kollmorgen explains, an encoder, Hall sensor or resolver reports rotor position to a drive, which keeps correcting the rotor's position and speed. The motor is only one part of the system; the drive and the feedback device matter as much.

Most servo motors are sold housed: stator, rotor, shaft, bearings, encoder and connector in one finished unit. A frameless motor is the same machine with almost everything but the working parts removed. Kollmorgen describes it as a kit of just a stator with copper windings and a rotor with rare-earth magnets mounted on a hub, which the customer builds into their own housing and bearings.

That is why robot makers use them. Without a housing, shaft and couplings, a joint can be smaller and lighter, and the large hollow centre lets cables pass through. Kollmorgen says frameless motors can drive a load directly or be combined with compact harmonic, planetary or cycloidal gears. It also notes that torque motors are the short, wide form of frameless motor, which gives the highest torque for a given volume.

How it fits into a robot joint

At Tesla AI Day 2022, Tesla said its Optimus rotary actuator pairs a bespoke permanent-magnet motor with a strain wave gear, a clutch and an output bearing. The usual joint is therefore a frameless motor feeding a harmonic reducer, with a driver and encoder alongside. Linear joints use a motor with a planetary roller screw. The motor is the part that sets the joint's torque and, with the reducer, its weight.

The rare-earth magnets are a direct cost input. Inovance's report says higher prices for magnetic steel, enamelled wire and power semiconductors weighed heavily on the profitability of its electric vehicle business in the first half of 2026 (2026 interim report, p. 23). Motors for robots draw on the same supply chain.

Where China stands

The two markets need to be kept apart.

Housed servo systems for factory machines. Inovance (汇川技术, 300124.SZ) says that in the first half of 2026 it held about 35.2% of China's general-purpose servo system market by revenue, ranking first, citing industry data provider MIR Databank (睿工业). Its servo revenue was about ¥4.8bn in the period, and it says its edge over foreign brands is customised industry solutions, value for money and fast delivery (2026 interim report, pp. 11, 23). The share is for servo systems across all industries, not for robot joints.

Frameless joint motors for robots. This is earlier, and three listed companies show different positions:

• Kinco (步科股份, 688160.SH) is the only one that discloses volumes. It shipped 113,600 frameless torque motors in the first half of 2026, up 422.9%, and has built a humanoid joint platform around frameless motors in sizes from 25mm to 120mm. Robots made up 54.4% of its revenue, including mobile robots, and it says it has made batch deliveries to several leading humanoid customers without naming them (2026 interim report, pp. 15, 16).
• Inovance lists frameless torque motors, low-voltage drives and roller screws among its humanoid parts. It says frameless motors are in small-batch use at leading humanoid makers, which it does not name (2026 interim report, pp. 13, 25).
• Haozhi (昊志机电, 300503.SZ) makes a frameless direct-drive motor for humanoid, collaborative and robot-dog joints and a frameless torque motor for collaborative and light robots. All of its robot core components, which include harmonic reducers, earned ¥17.3m in the first half of 2026, 1.5% of revenue (2026 interim report, pp. 14, 15, 25).

Others are moving the same way. Leadshine (雷赛智能, 002979.SZ) lists frameless torque motors, harmonic and planetary joint modules and dexterous hands as its mobile-robot components, but gives no robot revenue or volume (2026 interim report, pp. 9, 11).

The foreign incumbents are the motion-control specialists such as Kollmorgen, which publishes frameless catalogues for exactly these joints. The Chinese filings do not compare themselves with named foreign suppliers on frameless products, so we do not rank them.

Volumes and who buys

MIR Databank figures cited by Inovance put China's humanoid robot shipments at about 20,000 units in the first half of 2026, up 314% and already more than the whole of 2025 (2026 interim report, p. 18). Kinco's 113,600 frameless motors are therefore not all humanoid demand, since the same filing counts collaborative robots, mobile robots and other machines in its robot business. It does not say how many went into humanoids.

Our view: the filings describe two businesses. Housed servo is mature and domestic suppliers already lead their home market. Frameless joint motors are young: one listed company reports meaningful volume, another reports small batches, and a third reports robot parts as a small share of sales. The prize is large per robot, because a humanoid carries many joints, but the evidence that any Chinese supplier has locked in a leading humanoid maker is still thin and unnamed.

What to watch

• Named customers. None of the three filings names a humanoid maker for frameless motors. A named programme would be the first hard evidence of share.
• Humanoid share of motor volume. Kinco's unit growth is large, but a breakdown by robot type would show how much is humanoid.
• Magnet and material costs. Inovance reports raw material cost pressure and Kinco reports tight material supply that led it to build stock (2026 interim report, p. 8).
• Integration. Both Leaderdrive and Inovance are widening from single parts into joint modules, which would put pressure on stand-alone motor suppliers.