Frameless torque motor
Kollmorgen KBM / KBMS frameless torque motor
Frameless brushless rotor-and-stator kits for building the motor directly into a machine axis, with large through-bores and optional factory-fitted Hall sensors (KBMS).
Key specifications
| Bore (max) | 85 mm |
|---|---|
| Outer diameter | 60–190 mm |
| Peak torque (max) | 218 Nm |
| Continuous torque (max) | 54.6 Nm |
| Supply | 120-480 Vac windings (H insulation required above 240 Vac) |
| Feedback | digital Hall sensors (KBMS models) |
Summarised in our own words from Regal Rexnord Corporation's published data; series maxima, individual models vary. Last checked 2026-10-29. Source 1
Notes on this data
Only KBM 10 to KBM 45 data could be read from the selection guide; sizes KBM 57 to KBM 260 are listed in the guide but their data was not extracted, so the torque, OD and bore maxima here cover KBM 10-45 only and understate the full range. Peak 218 Nm row partly truncated. OD values rounded from 59.96 / 189.96 mm.
Specify Motion is not affiliated with Regal Rexnord Corporation. Kollmorgen and KBM / KBMS are used only to identify the product. Comparisons use published figures; always confirm against the current datasheet.
Typical applications
Alternatives that meet or exceed these figures
Engineers often come to us with a Kollmorgen part number and leave with an alternative that is easier to source, quicker to deliver or a better fit for the machine. These 3 series from our supply network are the closest match on published figures.
High-voltage (600 VDC) frameless torque motor kits from 110 to 360 mm with large through-bores and integrated Hall sensors; the high-torque end of the Akribis frameless range.
| Published maximum | KBM / KBMS | ADR-P |
|---|---|---|
| Continuous torque | 54.6 Nm | 365 Nm meets or exceeds |
| Peak torque | 218 Nm | 985.5 Nm meets or exceeds |
In-runner frameless torque motors from 65 to 410 mm stator OD with 8-64 poles, low profile and large through-holes; windings tailored to target speed.
| Published maximum | KBM / KBMS | TI Series In-Runner Frameless Direct D… |
|---|---|---|
| Continuous torque | 54.6 Nm | 70 Nm meets or exceeds |
| Peak torque | 218 Nm | — |
Housed iron-core direct drive rotary motors with bearings and optical encoder, 110-360 mm frames, up to about 1 kNm peak at 600 VDC.
| Published maximum | KBM / KBMS | ADR-A |
|---|---|---|
| Continuous torque | 54.6 Nm | 407.2 Nm meets or exceeds |
| Peak torque | 218 Nm | 1,017.9 Nm meets or exceeds |
| Speed | — | 2,000 rpm |
Figures are the highest published for each series and are not always measured the same way. A higher figure is not automatically a better choice: mounting, duty cycle, feedback, connectors and approvals matter too. An engineer will check the fit against your application before recommending anything.
What a frameless torque motor is
A frameless torque motor is a permanent-magnet brushless motor supplied as two parts, a rotor and a stator, with no housing, bearings or shaft. The machine builder mounts the rotor directly on the driven shaft and the stator in the machine structure, so the motor becomes part of the mechanism. Many have large through-holes and high pole counts, giving high torque at low speed with no gearbox. They need separate feedback, typically an encoder, and a servo drive.
When engineers choose a frameless torque motor
Choose a frameless motor when you want direct drive in a compact, integrated design, such as robot joints, gimbals, rotary tables and medical devices. Removing the gearbox eliminates backlash and improves stiffness and smoothness. The trade-offs are integration work and size: the builder supplies bearings, alignment, cooling and feedback, and torque per volume is lower than a geared solution. For off-the-shelf installation, a housed direct-drive motor may be simpler.
How to specify the Kollmorgen KBM / KBMS
Send these with your enquiry and an engineer can confirm the right KBM / KBMS variant or an equivalent:
- Continuous and peak torque (Nm)
- Speed (rpm)
- Outer diameter, bore and stack length (mm)
- Bus voltage and current (V, A)
- Thermal mounting and cooling
- Feedback type and resolution
- Air gap and concentricity tolerance (mm)
Common mistakes to avoid
- Leaving air gap and concentricity tolerances undefined
- Ignoring heat conduction from the stator into the housing
- Using an encoder with too low resolution for direct drive
- Forgetting rotor magnet attraction during assembly
Kollmorgen KBM / KBMS: frequently asked questions
What is the Kollmorgen KBM / KBMS?
Frameless brushless rotor-and-stator kits for building the motor directly into a machine axis, with large through-bores and optional factory-fitted Hall sensors (KBMS). Published series figures include bore 85 mm, outer diameter 60 mm, outer diameter 190 mm, peak torque 218 Nm. It is made by Regal Rexnord Corporation; Specify Motion can help source it or propose an equivalent.
Who makes the Kollmorgen KBM / KBMS?
The Kollmorgen KBM / KBMS is made by Kollmorgen (Regal Rexnord Corporation) and is listed here for engineers comparing options. Specify Motion is not affiliated with Regal Rexnord Corporation; brand names are used only to identify the product.
What is the bore of the Kollmorgen KBM / KBMS?
The published series maximum bore is 85 mm. Individual models and sizes in the KBM / KBMS range vary, so check the exact variant against your duty cycle, mounting and environment, or ask our engineers to confirm the right size for you.
Is there an alternative to the Kollmorgen KBM / KBMS?
Yes. On published figures, Akribis Systems ADR-P and TI Series In-Runner Frameless Direct Drive Torque Motors are the closest match from our supply network. An engineer confirms the fit against your application before recommending anything.
What is the difference between a frameless and a housed torque motor?
A frameless motor is only a rotor and stator; the machine provides bearings, shaft, housing and feedback. A housed direct-drive motor adds bearings, housing and encoder in a ready-to-install unit. Frameless suits compact, integrated designs where the machine already has stiff bearings; housed suits faster installation and simpler alignment.
Why use a frameless motor instead of a gearbox?
Direct drive removes backlash, wear and compliance in the gear train, giving smoother motion and stiffer control. It also allows a large hollow shaft for cabling. The trade-off is that torque must come from the motor alone, so it is larger for a given torque.
Further reading: How to select a frameless torque motor · Frameless motor sizing robot joints · Frameless and torque motors
Other frameless torque motor series
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