Futaba S-A400 Low Profile Digital Servo PWM/S.BUS2 8.0kg 0.08s 4.8V - 7.4V FUT05102741-3

Overview

The Futaba S-A400 Low Profile Digital Servo PWM/S.BUS2 is a precision-engineered aircraft servo designed for RC enthusiasts who demand high performance and compact dimensions. This coreless digital servo represents the pinnacle of Futaba's servo technology, offering exceptional speed, reliability and control for radio-controlled aircraft of all types. Whether you're flying aerobatic planes, scale models or high-speed jets, the S-A400 delivers the responsiveness and accuracy you need for smooth, precise flight control.

Built with a low profile case measuring just 40.5 × 20.0 × 25.4mm, this servo is perfect for tight installation spaces where traditional servos simply won't fit. The compact dimensions don't compromise on performance—this is a servo engineered for serious RC pilots who require professional-grade components. At only 46 grams, the S-A400 keeps your aircraft's weight to a minimum whilst delivering the torque and speed needed for demanding manoeuvres. Whether you're a seasoned RC aircraft pilot looking to upgrade your setup or a keen hobbyist building your first serious model aircraft, the S-A400 is a trusted choice from Futaba, a name synonymous with quality in the RC community since 1948.

Available from RC Model Shop, this servo comes fully supported with genuine Futaba components, expert advice and ongoing customer care. The S-A400 represents outstanding value for pilots seeking reliability and precision in their RC aircraft control systems.

Key Features

• S.BUS2 and PWM Protocol Support — The S-A400 supports both PWM and S.BUS2 command protocols, making it compatible with a wide range of RC transmitters and receivers used in the UK and across Europe, ensuring flexibility in your radio system choice.
• Coreless Digital Motor — The servo features a coreless motor design that provides superior efficiency and faster response times compared to traditional coreless motors, resulting in quicker command execution and smoother control inputs during flight.
• Metal Gears with Bearing Support — Precision-engineered metal gears with bearing support ensure durability and longevity, even during intensive use and demanding aerobatic manoeuvres, whilst maintaining consistent performance over time.
• Ultra-Fast Speed at 0.08 Seconds per 60° — At 7.4V, this servo achieves an impressive 0.08 seconds per 60 degrees of rotation, ensuring rapid response to pilot inputs and enabling precise control during high-speed flight and aerobatic routines.
• Exceptional Torque Output of 8.0kgf·cm — With 8.0 kilogram-force centimetres of torque at maximum voltage, the S-A400 delivers powerful, precise control authority suitable for control surfaces on aircraft ranging from small trainers to larger scale models.
• Low Profile Case Design — The compact, low profile case is engineered to fit into confined spaces within aircraft fuselages, allowing builders to optimise weight distribution and aerodynamic design without sacrificing servo performance.
• Wide Voltage Range 4.8V to 7.4V — The servo operates reliably across a broad voltage range from 4.8V up to 7.4V, providing flexibility in battery selection and allowing pilots to optimise performance and speed for their specific flying requirements.
• 25-Tooth Metal Spline (Ø6mm) — The standard 25-tooth spline with 6mm diameter shaft accepts a wide range of compatible servo horns and arms available from RC suppliers throughout the UK, simplifying setup and customisation.

Technical Performance

The Futaba S-A400 Low Profile Digital Servo represents a masterclass in servo engineering, combining cutting-edge technology with proven Futaba reliability. The coreless digital motor provides smooth, linear power delivery with minimal cogging, ensuring precise control inputs are translated faithfully to your aircraft's control surfaces. The motor design minimises vibration and noise whilst maximising efficiency, allowing longer flight times and reducing electrical noise that could interfere with receiver performance. The servo's aluminium final stage gear is paired with a 2-4 stage metal gear arrangement that distributes load evenly, reducing wear and extending the operational lifespan of the servo even under demanding use conditions. At 7.4V, the S-A400 achieves its maximum torque specification of 111.1 ounces-force per inch (8.0kgf·cm) and lightning-fast 0.08 second per 60 degree response time, making it suitable for high-performance aircraft and complex aerobatic routines. Even at the lower 6.0V operating point, performance remains excellent with 0.09 second response and 100 ounces-force per inch of torque available. The servo's digital circuit provides enhanced precision compared to analogue alternatives, enabling smoother transitions and more responsive control authority. The bearing-supported gear train reduces friction and ensures consistent performance across thousands of flight cycles, whether you're flying locally at UK airfields or competing in RC aircraft championships.

What's in the Box

• 1× Futaba S-A400 Low Profile Digital Servo
• Servo horns for standard applications
• Complete mounting hardware including brackets and fasteners

Frequently Asked Questions

• Is the Futaba S-A400 suitable for beginner RC aircraft pilots? — Whilst this servo is capable enough for beginner aircraft, it is truly designed for pilots who already have experience with RC flying and understand servo selection. Beginners may find it better value to start with more basic servos and upgrade to the S-A400 as they progress and build more advanced models. However, if you're committed to building quality aircraft from the start, this servo is absolutely suitable and will reward you with exceptional performance.
• What is the difference between PWM and S.BUS2 protocols on this servo? — PWM (Pulse Width Modulation) is the traditional analogue servo control method that has been used for decades in RC hobby applications and is supported by virtually all RC receivers. S.BUS2 is a modern digital protocol developed by Futaba that reduces wiring complexity (one signal wire instead of three), provides telemetry feedback, and allows more servos to be controlled with fewer receiver output channels. This servo supports both, giving you maximum compatibility.
• What battery should I use with the S-A400 servo? — The S-A400 operates across the range of 4.8V to 7.4V, making it compatible with 2-cell (2S) LiPo batteries at fully charged voltage, or conventional 4-cell NiMH receiver battery packs. For maximum performance, 7.4V (2S LiPo) is recommended, which will deliver the full 8.0kgf·cm torque and 0.08 second speed specifications. Many RC pilots power their servos from the same receiver battery that powers the receiver itself.
• How fast is the S-A400 compared to other aircraft servos? — At 0.08 seconds per 60 degrees at 7.4V, the S-A400 is exceptionally fast by aircraft servo standards. This speed is comparable to, or faster than, most standard aircraft servos on the market and makes it ideal for aerobatic flying where rapid control response is essential. The coreless motor design contributes significantly to this impressive speed without sacrificing torque.
• Can I use the S-A400 in an older RC aircraft with a standard receiver? — Yes, absolutely. The S-A400 supports traditional PWM control signals, so it will work with any standard RC receiver and transmitter combination currently in use in the UK. Simply connect the three servo wires (signal, power, ground) to your receiver in the normal way. You don't need a modern S.BUS receiver—the S.BUS2 capability is there if you want to use it in the future.
• What makes the metal gears in the S-A400 better than plastic alternatives? — Metal gears provide superior durability, reduce wear during intensive use, and maintain consistent performance over thousands of operating cycles. The bearing support on the gears further reduces friction, allowing smooth operation and extending the servo's lifespan significantly. This investment in quality materials is why Futaba servos are trusted by professional RC pilots worldwide.
• Is 46 grams a light servo for the torque it provides? — Yes, 46 grams is quite light for a servo delivering 8.0kgf·cm of torque. This low weight-to-power ratio is achieved through the coreless motor design and precision engineering, making the S-A400 excellent for weight-conscious aircraft builders who still need powerful control authority.

Why Buy from RC Model Shop?

RC Model Shop is a trusted UK RC retailer and authorised dealer for all the brands we stock, including Traxxas, ARRMA, Losi, FTX, Hobbywing, Spektrum and more. Based in Walsall, we have a physical store where customers are welcome to come in, view products and purchase in store. Whether you are a seasoned competitor, a weekend basher, or just discovering the world of RC for the first time, our team of experienced RC enthusiasts is here to help you find the perfect setup and provide ongoing support. Order the Futaba S-A400 Low Profile Digital Servo PWM/S.BUS2 8.0kg 0.08s 4.8V - 7.4V FUT05102741-3 today with confidence, knowing you are buying from an authorised retailer with genuine products, expert knowledge and a commitment to customer satisfaction. Shop online or visit us in Walsall — we look forward to helping you get the most out of your RC experience.