Smart servo actuator
Feetech STS series (TTL serial bus) smart servo actuator
TTL serial-bus smart servos with 360° magnetic encoders (4,096 steps per turn), from the 6 kg·cm (0.59 Nm) STS3045M at 6 V to the 200 kg·cm (19.6 Nm) brushless ST-3200 at 12 V (series maximum).
Key specifications
| Voltage (max) | 12 V |
|---|---|
| Data / bus | TTL half-duplex serial bus |
| Peak torque (max) | 19.6 Nm |
| Speed (max) | 170 rpm |
| Supply | 6 V, 7.4 V and 12 V models |
| Feedback | 360° magnetic encoder, 4,096 steps per turn |
| Weight | 210 g |
| Stall torque | 6 to 200 kg·cm (0.59 to 19.6 Nm) by model |
| Motor | cored, coreless and brushless versions |
Summarised in our own words from Shenzhen Feetech RC Model Co., Ltd.'s published data; series maxima, individual models vary. Last checked 2026-10-30. Source 1
Notes on this data
Stall torques are published in kg·cm and converted here (1 kg·cm = 0.0981 Nm). weight_g is the heaviest listed model (ST-3200). Page 2 of the STS list was not read.
Specify Motion is not affiliated with Shenzhen Feetech RC Model Co., Ltd.. Feetech and STS series (TTL serial bus) 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 Feetech 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.
Kinco's current-generation AC servo motor line, matched to the JD2 and FD5P PRO drives. Small-inertia 40-80 mm frames run at 3000 rpm on 220 V; large-inertia 130 and 180 mm frames are 1500 rpm machines reaching 47.8 Nm rated and 7.5 kW, with 23-bit multi-turn absolute encoders as standard.
| Published maximum | STS series (TTL serial bus) | SMK Series AC Servo Motors (SMK40S/60S… |
|---|---|---|
| Rated torque | — | 47.8 Nm |
| Peak torque | 19.6 Nm | 119.5 Nm meets or exceeds |
| Speed | 170 rpm | 6,000 rpm meets or exceeds |
| Power | — | 7,500 W |
Brushed permanent-magnet DC servomotors in 82 mm and 102 mm frames with a 9.5 V/krpm tachogenerator on every model. Continuous stall torque runs 0.5-4.5 Nm with peaks to 22 Nm, and the motors work with most brushed servo drives on the market.
| Published maximum | STS series (TTL serial bus) | BDS Series DC Brushed Servomotors (82B… |
|---|---|---|
| Rated torque | — | 4.3 Nm |
| Peak torque | 19.6 Nm | 22 Nm meets or exceeds |
| Speed | 170 rpm | 5,000 rpm meets or exceeds |
| Power | — | 964 W |
A complete AGV drive wheel combining servo motor, drive, reducer, brake and polyurethane tyre in one unit on 24-60 VDC with CANopen. Three published sizes (150, 165 and 180 mm wheels) give 3.6-40 Nm rated and up to 99 Nm peak at the wheel, for mobile robots carrying up to 1 tonne.
| Published maximum | STS series (TTL serial bus) | iWMC Integrated Servo Wheel |
|---|---|---|
| Rated torque | — | 40 Nm |
| Peak torque | 19.6 Nm | 99 Nm meets or exceeds |
| Speed | 170 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 smart servo actuator is
A smart servo actuator packages a small DC or brushless motor, a gear train, a position sensor and a microcontroller with motion control in one compact module. Each module is addressed on a shared serial bus, typically TTL or RS485, and can be commanded in position, velocity or current modes, with feedback on position, load, voltage and temperature. Units daisy-chain so multiple joints share one cable. They are widely used for robot joints in research, education and light service robots.
When engineers choose a smart servo actuator
Choose a smart servo for lightweight robot arms, grippers, humanoids and research platforms where quick integration and many networked joints matter more than industrial ratings. They are compact and simple to wire. The trade-offs are torque, precision and life: plastic or small metal gearing has backlash and limited torque, and duty cycles are lower than industrial servos. For production machines with heavy duty, an industrial servo with a gearbox is more appropriate.
How to specify the Feetech STS series (TTL serial bus)
Send these with your enquiry and an engineer can confirm the right STS series (TTL serial bus) variant or an equivalent:
- Stall and continuous torque (Nm)
- No-load speed (rpm)
- Supply voltage (V)
- Communication bus and protocol
- Position resolution and range
- Gear material and backlash
- Mass and form factor (g, mm)
Common mistakes to avoid
- Designing to stall torque instead of continuous working torque
- Ignoring gear backlash and compliance at the end of an arm
- Daisy-chaining too many joints on one power line
- Assuming industrial duty life from hobby-grade gearing
Feetech STS series (TTL serial bus): frequently asked questions
What is the Feetech STS series (TTL serial bus)?
TTL serial-bus smart servos with 360° magnetic encoders (4,096 steps per turn), from the 6 kg·cm (0.59 Nm) STS3045M at 6 V to the 200 kg·cm (19.6 Nm) brushless ST-3200 at 12 V (series maximum). Published series figures include voltage 12 V, peak torque 19.6 Nm, speed 170 rpm, weight 210 g. It is made by Shenzhen Feetech RC Model Co., Ltd.; Specify Motion can help source it or propose an equivalent.
Who makes the Feetech STS series (TTL serial bus)?
The Feetech STS series (TTL serial bus) is made by Feetech (Shenzhen Feetech RC Model Co., Ltd.) and is listed here for engineers comparing options. Specify Motion is not affiliated with Shenzhen Feetech RC Model Co., Ltd.; brand names are used only to identify the product.
What is the voltage of the Feetech STS series (TTL serial bus)?
The published series maximum voltage is 12 V. Individual models and sizes in the STS series (TTL serial bus) 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 Feetech STS series (TTL serial bus)?
Yes. On published figures, Kinco SMK Series AC Servo Motors (SMK40S/60S/80S, SMK130G, SMK180G) and BDS Series DC Brushed Servomotors (82BDS, 102BDS) 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 smart servo and an RC servo?
An RC servo is controlled by a pulse width signal and gives no feedback. A smart servo has an onboard controller on a digital bus, so it can report position, load, temperature and voltage, accept different control modes and be daisy-chained. This makes smart servos much better suited to robotics.
Are smart servos suitable for industrial machines?
Smart servos are typically designed for robotics research, education and light service robots. For heavy-duty production machines, industrial servo motors with gearboxes and drives give higher torque, precision and life, along with recognised safety functions. Smart servos can still suit light industrial tasks with modest duty.
Further reading: How to select an integrated servo motor · How to select a servo motor · Servo and stepper motors
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