Frameless torque motor
ETEL TMKi frameless torque motor
High-speed, high-torque frameless torque motors in six frame sizes (198 to 1,050 mm OD) with 76.3 to 11,600 Nm continuous, up to 20,600 Nm peak and up to 5,200 rpm, on a 600 V DC bus.
Key specifications
| Voltage (max) | 600 V |
|---|---|
| Outer diameter | 198–1,050 mm |
| Peak torque (max) | 20,600 Nm |
| Continuous torque (max) | 11,600 Nm |
| Speed (max) | 5,200 rpm |
| Cooling | Water cooling channels |
Summarised in our own words from DR. JOHANNES HEIDENHAIN GmbH's published data; series maxima, individual models vary. Last checked 2026-10-30. Source 1
Notes on this data
Mechanical interface compatible with TMB.
Specify Motion is not affiliated with DR. JOHANNES HEIDENHAIN GmbH. ETEL and TMKi are used only to identify the product. Comparisons use published figures; always confirm against the current datasheet.
Typical applications
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Our experienced engineers are on hand, ready to help with your project. Whether you need the ETEL TMKi itself, help sourcing it, or a modified or custom design built around your load, speed and space, tell us what the machine has to do and we'll come back with the right option.
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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 ETEL TMKi
Send these with your enquiry and an engineer can confirm the right TMKi 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
ETEL TMKi: frequently asked questions
What is the ETEL TMKi?
High-speed, high-torque frameless torque motors in six frame sizes (198 to 1,050 mm OD) with 76.3 to 11,600 Nm continuous, up to 20,600 Nm peak and up to 5,200 rpm, on a 600 V DC bus. Published series figures include voltage 600 V, outer diameter 198 mm, outer diameter 1,050 mm, peak torque 20,600 Nm. It is made by DR. JOHANNES HEIDENHAIN GmbH; Specify Motion can help source it or propose an equivalent.
Who makes the ETEL TMKi?
The ETEL TMKi is made by ETEL (DR. JOHANNES HEIDENHAIN GmbH) and is listed here for engineers comparing options. Specify Motion is not affiliated with DR. JOHANNES HEIDENHAIN GmbH; brand names are used only to identify the product.
What is the voltage of the ETEL TMKi?
The published series maximum voltage is 600 V. Individual models and sizes in the TMKi 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 ETEL TMKi?
Yes. Our engineers can propose an equivalent built around your load, speed and environment. 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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