Frameless Torque Motors for Robotics

Advanced Material Selection Guide

Frameless torque motor material selection directly determines achievable torque density, thermal stability at continuous rated load, and long-term magnetization retention.

• Magnet Grade — N50SH vs. N52 vs. N48UH: N50SH is the standard selection for frameless torque motors, providing high flux density (Br ~1.43 T) with a 150 °C operating temperature limit. N52 offers slightly higher Br but only a 60–80 °C temperature limit — unsuitable for motors embedded in thermally constrained machine frames. N48UH extends the operating temperature to 180 °C at a small flux density penalty, specified for high-ambient applications such as motors mounted adjacent to heated process equipment.
• Stator Lamination — 0.2 mm vs. 0.35 mm Silicon Steel: High-pole-count frameless motors operate at high electrical frequencies even at low mechanical speeds; 0.2 mm laminations are required above approximately 200 Hz to keep core losses below 5% of rated power. At low pole counts and low speeds (below 100 Hz), 0.35 mm laminations are adequate and provide better mechanical rigidity for large-diameter stators.
• Winding Wire — Round vs. Rectangular (Litz) Wire: Standard round magnet wire is used for most torque motor programs. Litz wire (multi-strand individually insulated conductors) reduces AC winding resistance at high electrical frequencies, beneficial for large-diameter motors with high pole counts where skin effect in standard round wire would increase resistive losses at rated speed.
• Stator Core Material — Silicon Steel vs. Cobalt-Iron Alloy: Silicon steel (M19) is the standard. Cobalt-iron alloy (Vacoflux 50) provides saturation flux density approximately 20% higher than silicon steel, enabling higher torque density in the same stator OD — specified for the highest-torque-density programs where frame size is an absolute constraint.
• Winding Insulation — Class H (180 °C) Standard: Class H is the minimum insulation class for frameless torque motors due to the embedded installation environment and high winding current density at peak torque. Class H epoxy varnish (rather than polyester-imide) is specified for additional chemical resistance in motors potted into aluminum machine structures where galvanic and thermal stress can degrade standard varnish over time.