FUT05102678-3

Overview

The Futaba S-U400 Standard Digital Servo PWM/S.BUS2 is a versatile and reliable servo solution designed for RC aircraft, helicopters, and surface vehicles. This compact standard-size servo delivers impressive performance with a maximum torque of 7.9kgf·cm at 7.4V and lightning-fast response times of just 0.13 seconds per 60-degree movement. Whether you're piloting a high-performance RC plane, managing rotor control on a helicopter, or fine-tuning surface vehicle steering, the S-U400 provides the precision control and robust engineering that serious RC enthusiasts demand. Built by Futaba, the pioneers of RC radio control since 1962, this servo represents decades of expertise in servo technology and control systems.

The S-U400 is engineered for UK RC hobbyists who demand reliability without compromise. Its dual-protocol compatibility with PWM and S.BUS2 command systems means it integrates seamlessly with modern Futaba radio systems and compatible aftermarket receivers, making it an excellent choice whether you're upgrading existing models or building new RC projects from scratch. The servo's compact dimensions of 40×20×38.1mm and lightweight construction at just 39 grams make it ideal for weight-sensitive applications where every gram counts. This is the servo for builders and pilots who understand that precision servo performance directly translates to better flight characteristics, faster lap times, and more predictable handling in all conditions.

Available through RC Model Shop, this is a genuine Futaba product backed by authorised dealer support and warranty protection. The S-U400 brings professional-grade servo technology to RC enthusiasts across the UK, whether you're a competition pilot, weekend flyer, or dedicated RC engineer.

Key Features

• S.BUS2 and PWM Protocol Support — This servo accepts both traditional PWM pulse width modulation commands and modern S.BUS2 digital protocols, giving you maximum compatibility with Futaba transmitters and receivers. This dual compatibility means you can use the S-U400 with both legacy systems and the latest Futaba radio technology, protecting your investment as you upgrade equipment over time.
• Exceptional Speed Performance — Delivering 0.13 seconds per 60-degree movement at 7.4V, the S-U400 responds with incredible quickness to control input. This rapid response time is critical for high-speed aerobatic flight, precision helicopter hovering, and sharp steering response in surface vehicles where millisecond-level responsiveness directly improves flight control and handling.
• Powerful Torque Output — Maximum torque reaches 7.9kgf·cm at 7.4V (equivalent to 109.7 oz/in), providing substantial power to move control surfaces even under high aerodynamic loads. Whether you're commanding large control surfaces on a high-wing aircraft, managing aggressive helicopter manoeuvres, or steering a heavily-loaded RC crawler, this torque ensures the servo never struggles or stalls.
• Wide Voltage Operating Range — Operating safely between 4.8V and 7.4V, the S-U400 performs reliably whether powered by four-cell NiMH packs, two-cell LiPo batteries, or three-cell LiPo systems. This flexibility means you can integrate this servo into virtually any RC platform you build, from vintage aircraft to modern high-voltage systems.
• 3-Pole Cored Motor — The servo features a sophisticated 3-pole cored motor design that delivers superior efficiency and heat dissipation compared to simpler motor configurations. This advanced motor construction ensures consistent performance throughout extended flying or operating sessions, maintaining speed and torque even during demanding use.
• Plastic Gearing with 6mm/25-Tooth Spline — The servo uses precision-engineered resin composite gearing coupled with a standard 6mm diameter spline shaft with 25-tooth configuration. This gearing arrangement balances durability with smooth operation, whilst the standard spline size ensures compatibility with a vast range of commercially available servo horns and control linkages across UK RC retailers.
• Compact Standard-Size Housing — Measuring just 40mm length, 20mm width, and 38.1mm height, and weighing merely 39 grams, the S-U400 fits standard servo mounting bays found on virtually every RC aircraft, helicopter, and vehicle platform. This standardisation makes retrofit and upgrades straightforward, whether you're working on kit builds or modifying existing models.
• Digital Circuit Technology — Unlike older analogue servos, the S-U400 employs full digital control electronics. This delivers more precise position control, better endpoint management, and easier integration with modern Futaba radio systems that support servo programming and diagnostics.

Technical Performance

The Futaba S-U400 represents the pinnacle of standard-size servo engineering, combining a robust 3-pole cored motor with precision digital control electronics. At 7.4V operating voltage, the servo achieves its maximum specified torque of 7.9kgf·cm with a phenomenally quick transit time of 0.13 seconds per 60-degree movement. Even at the lower 6.6V voltage, the servo still delivers respectable 0.14-second response time and 7.1kgf·cm torque, making it suitable for wider range of power systems. The servo's plastic resin gearing with 6mm/25-tooth spline provides an excellent balance between durability and smooth operation; whilst lighter than all-metal gearing, resin composite construction reduces servo weight significantly—crucial for aircraft where every gram impacts flight performance and battery endurance. The 39-gram overall weight places this servo among the lightest standard-size options available, making it perfectly suited to foam and balsa model aircraft, foam-tube helicopters, and weight-critical RC vehicles. The servo's operating voltage window from 4.8V to 7.4V is particularly clever, allowing integration into battery systems ranging from aged four-cell NiMH packs through modern two-cell and three-cell LiPo configurations. This flexibility, combined with PWM and S.BUS2 protocol support, makes the S-U400 an exceptionally versatile choice whether you're building classic control-line style aircraft or flying cutting-edge brushless-powered models with advanced radio systems.

What's in the Box

• 1× S-U400 Standard Digital Servo (black colour)
• Multiple servo horns (accessory pack included)
• Mounting hardware including fasteners

Frequently Asked Questions

• What voltage battery should I use with the S-U400 servo? — The S-U400 operates safely across a voltage range from 4.8V to 7.4V. You can power it with four-cell NiMH batteries (4.8V nominal), two-cell LiPo packs (7.4V nominal when fully charged), or three-cell LiPo systems. Performance improves at higher voltages: at 7.4V you'll get maximum torque of 7.9kgf·cm and fastest response of 0.13 seconds, whilst at 6.6V you'll see 7.1kgf·cm torque and 0.14-second response. Choose your voltage based on your model's weight and control requirements.
• Is the S-U400 suitable for beginner RC pilots? — Yes, the S-U400 is excellent for both beginners and experienced pilots. The servo's fast response and strong torque make it forgiving in flight control, helping newer pilots maintain stability. Its standard size and common 6mm/25-tooth spline means it works with servo horns and linkages you'll find at every RC retailer across the UK. The servo's simplicity of installation—it requires only a power connection and signal wire to your receiver—makes setup straightforward for first-time builders.
• What's the difference between PWM and S.BUS2 protocols on the S-U400? — PWM (pulse width modulation) is the traditional servo control method where each servo wire carries a separate signal. S.BUS2 is Futaba's modern digital protocol that transmits data for multiple servos down a single wire, reducing wiring complexity and weight on your model. The S-U400 supports both, so you can use it with any Futaba system or compatible aftermarket receiver, whether your radio system uses traditional or modern protocols.
• How much torque does the S-U400 produce, and what does it mean? — The servo produces 7.9kgf·cm (kilogram-force centimetres) at maximum voltage. This unit describes rotational force: if you attached a 1-kilogram weight at a 1-centimetre radius from the servo's rotation point, the servo could hold it. In practical terms, this torque level easily moves large aircraft control surfaces like elevators and rudders, manages helicopter main rotor head cyclic control, and steers even large-scale RC trucks and crawlers.
• Will this servo fit my RC model? — The S-U400 is a standard-size servo measuring 40×20×38.1mm, which is the industry-standard size. It will fit any servo bay designed for standard servos, which includes the vast majority of RC aircraft kits, helicopter platforms, and surface vehicle frames sold in the UK. The 6mm/25-tooth spline is also standard, making servo horns universally compatible with thousands of aftermarket options.
• How long will the servo last? — The S-U400 is built with precision engineering and proven Futaba reliability. Lifespan depends on usage: servos used for gentle flying or driving will last many years, whilst servos subjected to aggressive aerobatics or constant high-speed operation will wear faster. The plastic gearing is perfectly adequate for most users, though if you operate your model extremely intensively, you could consider upgrading to all-metal gearing versions in future if they become available.
• Can I use this servo with non-Futaba receivers? — The S-U400 supports both PWM and S.BUS2 protocols. PWM is universal and works with virtually any receiver. S.BUS2 is Futaba's proprietary protocol, so for S.BUS2 compatibility you'll need a Futaba receiver or an aftermarket receiver that specifically supports S.BUS2. However, using PWM protocol, the S-U400 will work with any standard receiver from any manufacturer, giving you ultimate flexibility in building your RC system.

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-U400 Standard Digital Servo PWM/S.BUS2 7.9kg 0.13s 4.8V - 7.4V 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.