Frameless torque motor FMK series

for roboticslow-noiselow-vibration

Introduction
Frameless torque motors consist only of stator and rotor assemblies, offering flexible configuration and simplified integration compared with framed servo motors. As drive systems trend toward higher integration, frameless motors eliminate the need to account separately for motor interfaces in system design, minimizing the space occupied by the power output unit and enabling greater overall system integration. HONPINE FMK frameless torque motors are used across J1–J6 joints of collaborative and dual-arm robots, walking joints of quadruped robots and flexible joints of humanoid robots.

Designer speaking
To meet rising customer demands for core joint components, HONPINE introduced the fourth-generation FMK series frameless torque motor. The FMK series refines stator welding and improves stator roundness to maintain performance while reducing motor length. The design adopts a larger split ratio and an increased hollow section with an optimized rotor manufacturing process, better supporting embodied intelligent products and helping to reduce customers' total cost of ownership (TCO). Size coverage has been expanded to match mainstream joint-module specifications on the market.

Features

• Expanded size coverage: available outer diameters include 25/38/43/50/60/70/85/115/140/160 mm.
• Large split ratio and enlarged hollow design with increased rotor inner diameter to facilitate wire routing and PCB layout for humanoid robot mechanisms.
• Process optimizations reduce motor weight and increase power density, supporting lightweight embodied intelligent products.
• Improved potting and electromagnetic optimization deliver better temperature-rise performance.
• Low noise and vibration to enhance motion coordination in embodied intelligence systems.

Specification — Sheet 1 (values per model)
Model | Rated power Pn(W) | Rated speed Nn(rpm) | Mechanical time constant tm(ms) | Torque constant Kt(Nm/A) | Rated torque Tn(N.m)
FMK02509-0004-5511-7DP02 — Pn: 36 W; Nn: 5500 rpm; tm: 0.576 ms; Kt: 0.041 Nm/A; Tn: 0.063 N.m
FMK03807-0005-3518N-7DP02 — Pn: 50 W; Nn: 3500 rpm; tm: 0.95 ms; Kt: 0.089 Nm/A; Tn: 0.135 N.m
FMK04311-0008-3725N-7DP02 — Pn: 77 W; Nn: 3700 rpm; tm: 0.068 ms; Kt: 0.099 Nm/A; Tn: 0.2 N.m
FMK05008-0016-5030N-10DP02 — Pn: 157 W; Nn: 5000 rpm; tm: 0.61 ms; Kt: 0.089 Nm/A; Tn: 0.3 N.m
FMK06018-0020-2028N-10DP02 — Pn: 209 W; Nn: 2000 rpm; tm: 0.51 ms; Kt: 0.172 Nm/A; Tn: 1 N.m
FMK06018-0026-3628N-10DP02 — Pn: 264 W; Nn: 3600 rpm; tm: 1.91 ms; Kt: 0.103 Nm/A; Tn: 0.7 N.m
FMK07011-0025-3642N-10DP02 — Pn: 252 W; Nn: 3650 rpm; tm: 0.48 ms; Kt: 0.116 Nm/A; Tn: 0.66 N.m
FMK08513-0037-2952N-10DP02 — Pn: 370 W; Nn: 2950 rpm; tm: 1.1 ms; Kt: 0.14 Nm/A; Tn: 1.2 N.m
FMK08523-0073-3542N-10DP02 — Pn: 732 W; Nn: 3500 rpm; tm: 1.02 ms; Kt: 0.134 Nm/A; Tn: 2 N.m
FMK11525-0117-3260N-10DP02 — Pn: 1173 W; Nn: 3200 rpm; tm: 1.15 ms; Kt: 0.127 Nm/A; Tn: 3.5 N.m

Specification — Sheet 2 (mechanical dimensions by model)
Frame (mm) / Stator / Coil / Rotor / Total height H
Header: Frame(mm) — Outside diameter D1; Stator: Iron core height H1 / Outside diameter D2; Coil: Inside diameter d1 / Inside diameter d2; Rotor: Iron core height H2 / Total height H
FMK02509-0004-5511-7DP02 — D1: 25; H1: 9.2; D2: 24.5; d1: 15.8; d2: 11.6; H2: 10.3; Total height H: 16.35
FMK03807-0005-3518N-7DP02 — D1: 38; H1: 7; D2: 36.6; d1: 24; d2: 18; H2: 8.1; Total height H: 13.8
FMK04311-0008-3725N-7DP02 — D1: 43; H1: 11; D2: 42.3; d1: 31.3; d2: 25.5; H2: 12.1; Total height H: 20
FMK05008-0016-5030N-10DP02 — D1: 50; H1: 8.6; D2: 49; d1: 36.5; d2: 30; H2: 11.5; Total height H: 16
FMK06018-0020-2028N-10DP02 — D1: 60; H1: 18; D2: 58.5; d1: 46.2; d2: 39.2; H2: 22; Total height H: 29.2
FMK06018-0026-3628N-10DP02 — D1: 60; H1: 18; D2: 58.5; d1: 46.2; d2: 39.2; H2: 22; Total height H: 29.2
FMK07011-0025-3642N-10DP02 — D1: 69; H1: 11; D2: 66; d1: 49.6; d2: 42; H2: 15; Total height H: 19.6
FMK08513-0037-2952N-10DP02 — D1: 85; H1: 13; D2: 83; d1: 61.6; d2: 52; H2: 15; Total height H: 23.35
FMK08523-0073-3542N-10DP02 — D1: 85; H1: 23.5; D2: 83; d1: 61.6; d2: 52; H2: 25; Total height H: 33.8
FMK11525-0117-3260N-10DP02 — D1: 115; H1: 26; D2: 112; d1: 87; d2: 60; H2: 26; Total height H: 45

Characteristics / technical specifications

• Series name: FMK series frameless torque motors (4th generation).
• Applications: J1–J6 joints of collaborative and dual-arm robots; walking joints of quadruped robots; flexible joints of humanoid robots.
• Available outer diameters: 25, 38, 43, 50, 60, 70, 85, 115, 140, 160 mm.
• Design highlights: large split ratio, enlarged hollow design and increased rotor inner diameter to facilitate wiring and PCB layout.
• Electrical/mechanical sample data: rated power from 36 W up to 1173 W (models listed above); rated speeds ~2000–5500 rpm; rated torques ~0.063–3.5 N.m in listed models.
• Manufacturing improvements: optimized stator welding and roundness, rotor process optimization, potting and electromagnetic improvements for thermal control.
• Performance benefits: increased power density, reduced weight, improved temperature-rise control, low noise and vibration.