A frameless motor is only the stator and rotor. You build the rest of the actuator around it, which gives the most compact joint possible.
What you provide
- Housing and shaft that hold the stator and rotor concentric with a small, even air gap.
- Bearings sized for the joint’s loads, since the motor has none.
- Encoder, often a magnetic or optical ring on the output, for field-oriented control and position.
- Driver (FOC motor controller) matched to the motor’s voltage, current and pole count.
- A heat path: the stator is the hot part, so bond or press it into a housing that can shed heat.
Inrunner or outrunner
- Inrunner: the rotor sits inside the stator. A large hollow center leaves room for cables, a shaft or a gear stage, and the stator is easy to cool through the housing.
- Outrunner: the rotor turns outside the stator. For the same outer diameter it gives more torque, which suits flat quasi-direct-drive joints.
Reading the numbers
- KV is speed per volt with no load. Lower KV means more torque per amp and less speed per volt.
- Peak torque is limited by current and magnet saturation; rated torque by heat. Your housing’s cooling decides how close you get to the rated figure.
- Hall sensors, where offered, make start-up commutation simpler before the encoder is aligned.
Adding a reduction
Most custom joints add a planetary or cycloidal stage inside the rotor or beside it. See quasi-direct drive or high ratio for how the ratio changes the joint’s behavior.
Browse frameless torque motors and ask us for drawings and datasheets when you request a quote.