Frameless torque motor
ETEL TMB+ frameless torque motor
ETEL's main water-cooled frameless torque motor range: 62 models from 160 to 1,288 mm outer diameter, 21.6 to 22,300 Nm continuous and up to 42,900 Nm peak, and up to 4,590 rpm on the smallest size.
Key specifications
| Outer diameter | 160–1,288 mm |
|---|---|
| Peak torque (max) | 42,900 Nm |
| Continuous torque (max) | 22,300 Nm |
| Speed (max) | 4,590 rpm |
| Cooling | Water cooling channels (open or closed versions) |
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 · Source 2
Notes on this data
Up to 20% more torque density and 30% lower losses than TMB, mechanically compatible.
Specify Motion is not affiliated with DR. JOHANNES HEIDENHAIN GmbH. ETEL and TMB+ 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 TMB+ 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 TMB+
Send these with your enquiry and an engineer can confirm the right TMB+ 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 TMB+: frequently asked questions
What is the ETEL TMB+?
ETEL's main water-cooled frameless torque motor range: 62 models from 160 to 1,288 mm outer diameter, 21.6 to 22,300 Nm continuous and up to 42,900 Nm peak, and up to 4,590 rpm on the smallest size. Published series figures include outer diameter 160 mm, outer diameter 1,288 mm, peak torque 42,900 Nm, continuous torque 22,300 Nm. It is made by DR. JOHANNES HEIDENHAIN GmbH; Specify Motion can help source it or propose an equivalent.
Who makes the ETEL TMB+?
The ETEL TMB+ 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 outer diameter of the ETEL TMB+?
The published series minimum outer diameter is 160 mm. Individual models and sizes in the TMB+ 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 TMB+?
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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Tell us about your project and how you use the ETEL TMB+: the load, speed, duty and environment. An experienced engineer will review it and reply, normally within one working day.
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