| 20KG·CM STALL | 0.030S/60° NO-LOAD | 12V RATED |
| 78G WEIGHT | StainlessGEARTRAIN | 360°TRAVELCustomizable |
Overview
The BLS8120H is a tail servo, and the spec sheet reads like one: a 510–1010 µs pulse window with 760 µs neutral rather than the usual 1000–2000 / 1500. That narrow window is what lets a tail gyro command fine corrections without the resolution loss of a full-range channel.
The case is the standard 20 × 40 × 38 mm aluminium block at 78 g, with a stainless steel geartrain on two ball bearings and a 25T-φ5.96 mm spline. Built-in motor is brushless, and the lead is 300 mm of 22 AWG.
This page covers the PWM build: a standard 50–333 Hz pulse input, 1500 µs neutral and a 3–4 µs dead band. It is the version to pick when the servo hangs off a receiver or a flight controller and you want nothing between the two.
Performance at each supply voltage
| Supply | No-load speed | Peak stall torque | Idle current | Stall current |
|---|---|---|---|---|
| 7.4 V | 0.050 s/60° (1200 °/s) | 12.5 kg·cm (1.23 N·m / 174 oz·in) | 320 mA | 2.8 A |
| 8.4 V | 0.044 s/60° (1364 °/s) | 15 kg·cm (1.47 N·m / 208 oz·in) | 370 mA | 3.5 A |
| 12 V | 0.030 s/60° (2000 °/s) | 20 kg·cm (1.96 N·m / 278 oz·in) | 440 mA | 4.0 A |
Control specification
| Item | Specification |
|---|---|
| Command signal | PWM |
| Amplifier | Digital controller |
| Pulse width range | 510–1010 µs |
| Neutral position | 760 µs |
| Dead band | 1 µs |
| Rotating direction | CCW (510–1010 µs) |
| Travel | 360°, customizable |
Mechanical specification
| Item | Specification | Item | Specification |
|---|---|---|---|
| Dimensions | 20 × 40 × 38 mm | Case material | Aluminium, CNC |
| Weight | 78 g | Geartrain | Stainless steel |
| Bearings | 2 × ball bearing | Motor | Brushless |
| Output spline | 25T-φ5.96 mm | Horn | Plastic, POM |
| Lead / connector | 300 mm, 22 AWG | Mechanical limit | 210° |
| Operating temperature | −15 °C to 65 °C | Storage temperature | −20 °C to 70 °C |
| Ingress protection | Splash resistant (customizable) | Travel | 360°, customizable |
What’s in the box
- 1 × XQ-BLS8120H servo
- 1 × POM horn set
- 1 × mounting screw pack
Optional: metal horn, sold separately.
How to size it
The pulse window is not the standard one. 510–1010 µs with 760 µs neutral means a default 1000–2000 µs output will drive it to one end stop — set the radio or gyro to the narrow tail window before the first power-up.
Torque at 8.4 V is 15 kg·cm at 0.044 s/60°; on 12 V it is 20 kg·cm at 0.03 s/60°. Stall current stays at or under 4 A, so a 5 A BEC is enough for one, but not for a tail plus three swashplate servos on the same rail.
FAQ
Why is the pulse range 510–1010 µs?
It is a tail-servo window, not a standard channel. Set the gyro or radio to the narrow tail pulse range — feeding it 1000–2000 µs will drive the output against the mechanical limit.
What is the neutral position?
760 µs, i.e. the centre of the 510–1010 µs window. Do not assume 1500 µs.
What pulse range does it accept?
The inspection sheet specifies a 500–2500 µs window (800–2200 µs on the 9130/9150) with 1500 µs neutral, both customizable at order. Feeding it outside that window is out of spec.
Can I drive it from a normal receiver?
Signal-wise yes, but check the supply. This servo wants 8.4–16.8 V, not a 6 V receiver pack, so the power rail has to be separate from the receiver’s.
Other interfaces
Downloads
- XQ-BLS8120H inspection specification (PDF, 845 KB)
Torque, speed and current at each supply voltage, mechanical data, control specification, mounting dimensions. - 2D dimension drawing (image)
Mounting hole positions, case depth and overall height; the same drawing is inside the datasheet.
