DC servo motor
FAULHABER BXT DC servo motor
Flat outer-rotor brushless motors with a high torque-to-length ratio, offered with or without housing.
Key specifications
| Outer diameter | 22–42 mm |
|---|---|
| Rated torque (max) | 0.134 Nm |
| Speed (max) | 10,000 rpm |
| Power (max) | 100 W |
| Voltage | 6-48 V |
Summarised in our own words from Dr. Fritz Faulhaber GmbH & Co. KG's published data; series maxima, individual models vary. Last checked 2026-10-29. Source 1
Notes on this data
Faulhaber lists 'torque up to' per series without saying whether it is continuous or peak; stored as torque_Nm_rated_max (converted from mNm). 4221 BXT R (unhoused) 134 mNm / 100 W. Page length figures inconsistent for 4221 BXT H (21 vs 22 mm).
Specify Motion is not affiliated with Dr. Fritz Faulhaber GmbH & Co. KG. FAULHABER and BXT 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 FAULHABER 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.
A single 110 mm, 1.2 kW, 48 VDC servo motor giving 4 Nm at 3000 rpm for higher-power low-voltage systems, paired with Kinco FD1 and OD drives.
| Published maximum | BXT | SMH Series Low-Voltage DC Servo Motor … |
|---|---|---|
| Rated torque | 0.13 Nm | 4 Nm meets or exceeds |
| Speed | 10,000 rpm | — |
| Power | 100 W | 1,200 W meets or exceeds |
Leadshine low-voltage PMSM servo motors from a 25 mm 33 W unit up to a 130 mm 2 kW unit, wound for 24-60 V DC buses. Fully published data covers torque to 6.4 Nm rated / 16 Nm peak, 17-bit absolute or 2500 ppr incremental encoders and IP65. Designed for ELD2, 2ELD2 and ELD3 drives.
| Published maximum | BXT | ELVM Series Low-Voltage DC Servo Motors |
|---|---|---|
| Rated torque | 0.13 Nm | 6.4 Nm meets or exceeds |
| Peak torque | — | 16 Nm |
| Speed | 10,000 rpm | 6,000 rpm |
| Power | 100 W | 2,000 W meets or exceeds |
Low-voltage brushless DC servo motors for 48 or 96 VDC systems, with a 12-slot/10-pole design, matched to the Kinco FD1X5 drive and aimed at robotics, CNC and automated lines.
| Published maximum | BXT | SMK Series Low-Voltage DC Servo Motors |
|---|---|---|
| Rated torque | 0.13 Nm | — |
| Speed | 10,000 rpm | — |
| Power | 100 W | 5,000 W meets or exceeds |
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 DC servo motor is
A DC servo motor, in current usage, is usually a low-voltage brushless permanent-magnet motor designed to run from a DC bus, typically 24 to 96 V, under closed-loop servo control. Electronically it works like an AC servo, with a three-phase stator commutated by the drive and encoder or Hall feedback on the shaft. The lower voltage means higher current for the same power, but suits battery-powered and safety-extra-low-voltage machines. Small precision brushless servomotors also fall into this group.
When engineers choose a DC servo motor
Choose a low-voltage DC servo for mobile robots, AGVs, battery equipment, medical devices and compact machines where mains voltage is impractical or unsafe. It allows simple power distribution and safe access. The trade-offs are current and power range: high current means thicker cables and higher losses, so power is typically limited to a few kilowatts. For mains-powered machines above that, an AC servo is usually simpler.
How to specify the FAULHABER BXT
Send these with your enquiry and an engineer can confirm the right BXT variant or an equivalent:
- Bus voltage (V DC) and battery range
- Continuous and peak torque (Nm)
- Rated and maximum speed (rpm)
- Continuous and peak current (A)
- Feedback type and resolution
- Brake, IP code and frame size (mm)
- Drive and network interface
Common mistakes to avoid
- Sizing at nominal battery voltage without checking the low-charge end
- Undersizing cables for the higher current
- Ignoring regenerative energy into a battery or supply
- Mixing motor and drive feedback types that are not compatible
FAULHABER BXT: frequently asked questions
What is the FAULHABER BXT?
Flat outer-rotor brushless motors with a high torque-to-length ratio, offered with or without housing. Published series figures include outer diameter 22 mm, outer diameter 42 mm, rated torque 0.134 Nm, speed 10,000 rpm. It is made by Dr. Fritz Faulhaber GmbH & Co. KG; Specify Motion can help source it or propose an equivalent.
Who makes the FAULHABER BXT?
The FAULHABER BXT is made by FAULHABER (Dr. Fritz Faulhaber GmbH & Co. KG) and is listed here for engineers comparing options. Specify Motion is not affiliated with Dr. Fritz Faulhaber GmbH & Co. KG; brand names are used only to identify the product.
What is the outer diameter of the FAULHABER BXT?
The published series minimum outer diameter is 22 mm. Individual models and sizes in the BXT 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 FAULHABER BXT?
Yes. On published figures, Kinco SMH Series Low-Voltage DC Servo Motor (SMH110D) and Leadshine ELVM Series Low-Voltage DC Servo 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 an AC servo and a DC servo motor?
Both are typically brushless permanent-magnet motors under closed-loop control. The main difference is the supply: AC servos are wound for drives fed from mains voltage, while DC servos are wound for low-voltage DC buses. DC servos suit battery and low-voltage machines; AC servos suit higher-power mains machines.
How does battery voltage affect a DC servo motor?
Motor speed is roughly proportional to available voltage, so as a battery discharges the top speed falls. Size the motor at the lowest working battery voltage. Also allow for regenerative energy during braking, which raises bus voltage and must be absorbed by the battery or a braking circuit.
Further reading: How to select a servo motor · How to select a dc motor · Servo and stepper motors
Other dc servo motor series
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