Overview

The Futaba S-U400 Standard Digital Servo is a professional-grade control solution purpose-built for RC aircraft, helicopters and surface models that demand reliable, precise servo actuation. As a digital servo with integrated S.Bus2 capability, the S-U400 combines modern digital control protocol support with classic PWM compatibility, making it exceptionally versatile across different RC radio systems. This bulk 10-piece pack (part number FUT05102679-3-B) represents outstanding value for fleet builds, RC clubs, multi-model setups and enthusiasts who need consistent performance across numerous aircraft or surface platforms without compromise.

Whether you are operating a fleet of trainers, maintaining club equipment, or building multiple RC aircraft simultaneously, the S-U400 delivers the torque, speed and reliability that serious RC hobbyists expect from a Futaba servo. The compact standard-size format integrates seamlessly into conventional servo bays found across RC aeroplanes, helicopters and surface vehicles throughout the UK RC community. With over 60 years of heritage in RC control systems, Futaba engineering ensures that every S-U400 servo meets exacting manufacturing standards, delivering consistent response and smooth, precise movement across typical RC aircraft applications with minimal variance between units.

Each servo in this bulk pack arrives complete with mounting hardware and servo horns, enabling immediate installation without purchasing additional components. The S-U400 represents a mature, proven design that has earned respect among RC modellers seeking dependable control without premium pricing, making this pack particularly attractive for serious hobbyists and club operators across the RC car UK market and wider RC community.

Key Features

• PWM and S.Bus2 Dual Protocol Support — The S-U400 accepts command signals via conventional PWM control and advanced S.Bus2 digital protocol, ensuring compatibility with legacy RC radio systems and modern digital receivers including Futaba equipment, eliminating the need to purchase separate servos for different aircraft or radio systems.
• Strong Torque Output Across Voltage Range — Delivering 7.9 kgf·cm of torque at 7.4V and 7.1 kgf·cm at 6.6V, the S-U400 commands sufficient force for reliable operation of control surfaces across typical RC aircraft, from trainers to intermediate aerobatic platforms, handling both primary flight control surfaces and secondary systems with confidence.
• Fast Response Speed for Precise Control — With a transit time of 0.13 seconds across a 60-degree arc at 7.4V and 0.14 seconds at 6.6V, the S-U400 delivers rapid control surface movement, enabling sharp, responsive handling that translates to improved flight characteristics and precise manoeuvring during flight operations.
• Compact Standard-Size Dimensions — Measuring just 40 × 20 × 38.1 millimetres, the S-U400 fits comfortably into standard servo bays found across RC aircraft, helicopters and surface models throughout the UK RC hobby community, maximising design flexibility without architectural compromise.
• Lightweight Construction at 39 Grammes — Weighing only 39 grammes per unit, the S-U400 contributes minimal mass to your RC model, helping maintain optimal centre of gravity and reducing overall model weight, critical considerations for flight performance and battery endurance.
• Digital Circuit Architecture — The S-U400 utilises digital servo circuitry for enhanced control resolution and reduced drift compared to analogue servos, delivering more precise positioning and improved holding force when the control surface is centred, important for aerobatic and precision flying disciplines.
• Durable Plastic Gearing with 25-Tooth Spline — The servo incorporates 6-millimetre diameter resin plastic gearing with a 25-tooth output spline, engineered for smooth, reliable operation in typical RC applications whilst maintaining cost-effectiveness and reducing noise compared to metal gearing.
• 3-Pole Cored Motor Design — The S-U400 features a purpose-designed 3-pole cored motor that delivers consistent torque characteristics and responsive speed across the 4.8V to 7.4V operating voltage range, ideal for LiPo battery-powered RC systems.
• Supplied as 10-Unit Bulk Pack — This comprehensive bulk pack includes ten complete S-U400 servos, servo horns and mounting hardware, perfect for clubs, competition teams and multi-model operators seeking to standardise their servo equipment across a fleet with significant cost savings compared to individual servo purchases.
• Wide Voltage Compatibility 4.8V to 7.4V — The S-U400 operates reliably across the standard voltage range supported by 2S LiPo batteries and NiMH battery packs, allowing flexible power system integration across your RC aircraft collection without component limitations.

Technical Performance

The Futaba S-U400 Standard Digital Servo represents a mature engineering solution combining proven Futaba digital servo architecture with practical performance characteristics suited to modern RC aircraft operations. At 7.4V, representing a fully charged 2S LiPo battery typical in many RC aeroplanes, the S-U400 generates 7.9 kilogrammes-force centimetres of torque with a 0.13-second transit time across 60 degrees of rotation, delivering rapid, authoritative control surface response. Operating at 6.6V, closer to mid-discharge battery conditions, the servo maintains respectable output of 7.1 kilogrammes-force centimetres with a 0.14-second transit time, demonstrating consistent performance even as battery voltage depletes during extended flight sessions. In imperial measurements relevant to some RC modellers, the servo delivers 109.7 ounces-inches of torque at 7.4V and 98.6 ounces-inches at 6.6V. The 3-pole cored motor provides reliable actuation across this voltage band, engineered specifically for the responsive demands of RC flight control. The servo incorporates resin plastic gearing with a 6-millimetre spline diameter and 25-tooth output, a proven combination balancing durability with cost-effectiveness in standard-class servo applications. Digital circuit design ensures enhanced control resolution and holding precision compared to analogue servo alternatives, reducing drift and improving flight stability during hands-off manoeuvres or sustained control inputs. The compact 40 × 20 × 38.1-millimetre form factor positions the S-U400 within standard servo dimensions, facilitating installation into conventional servo bays across Futaba-equipped RC aircraft and complementing installations in systems using PWM or S.Bus2 compatible receivers. At 39 grammes per unit, the servo contributes negligible mass penalty, critical for aircraft weight budgets where every gramme affects climb rate, endurance and flight envelope performance. Colour-coded black plastic construction provides durability and professional appearance, with mounting lugs engineered for reliable installation using standard RC hardware.

What's in the Box

• 10x Futaba S-U400 Standard Digital Servos
• Servo horns (multiple types for different control surface applications)
• Mounting hardware including fasteners and securing brackets

Frequently Asked Questions

• Is the Futaba S-U400 suitable for beginner RC aircraft pilots? — Yes, the S-U400 is an excellent choice for beginners transitioning from trainer aircraft to intermediate models. The straightforward PWM compatibility integrates with any standard RC radio system, whilst S.Bus2 capability future-proofs your investment if you upgrade to modern Futaba digital receivers. At 7.9 kilogrammes-force centimetres of torque, it commands sufficient force for reliable aileron, elevator and rudder actuation on typical trainer and sport aircraft. The proven digital servo architecture delivers the precise control response that developing pilots need to build confidence.
• What battery voltage does the S-U400 require? — The S-U400 operates across a 4.8V to 7.4V range, directly compatible with 2S LiPo battery packs commonly used in modern RC aircraft throughout the UK RC hobby. The servo also functions with traditional NiMH battery packs delivering equivalent voltage. At higher voltages closer to 7.4V, the servo delivers maximum torque and speed; at lower voltages approaching battery discharge, performance degrades slightly but remains serviceable. Most operators standardise on 2S LiPo batteries (nominally 7.4V when fully charged, around 6.6V at mid-discharge), which deliver reliable S-U400 performance across a typical RC flight session.
• Can the S-U400 work with my existing Futaba radio system? — Absolutely. The S-U400 supports three command protocols: traditional PWM control compatible with any RC radio system and receiver, plus S.Bus and advanced S.Bus2 digital protocols supported by modern Futaba receivers. This triple compatibility ensures the servo operates seamlessly with vintage and contemporary Futaba radio equipment, and functions with non-Futaba radios via standard PWM servo connections. If you operate a mixed fleet of Futaba and non-Futaba aircraft, standardising on S-U400 servos simplifies inventory management and enables servo swapping between models without compatibility concerns.
• How does the S-U400 compare to other standard-size servos? — The S-U400 occupies the mid-range of the standard servo market, delivering solid torque (7.9 kilogrammes-force centimetres) and responsive speed (0.13 seconds per 60 degrees) at reasonable cost. Compared to budget servos, the S-U400 benefits from digital servo circuitry providing enhanced control resolution and reduced drift. Compared to premium servo options, the S-U400 trades some additional weight savings and marginally higher torque for significantly lower cost, making it exceptional value for fleet operations, club equipment and multi-model setups. The plastic gearing strikes a practical balance between durability and economy; metal-geared servos offer enhanced longevity but at substantially higher cost justified primarily in competition or high-cycle applications.
• Is this bulk 10-piece pack suitable for my RC club? — Ideally suited. Clubs operating teaching fleets, competition aircraft or shared equipment benefit substantially from standardised servo equipment. The S-U400 bulk pack at 10 units enables complete servo upgrade across a modest training fleet, ensures consistent spare parts inventory, and reduces per-unit cost compared to purchasing individual servos. Each servo arrives complete with horns and mounting hardware, enabling rapid installation and standardisation across your club's aircraft.
• What is the weight impact of S-U400 servos on my RC aircraft? — At 39 grammes per servo, the S-U400 contributes minimal mass to your aircraft. A typical three-servo control setup (ailerons, elevator, rudder) adds approximately 117 grammes to your airframe, a negligible penalty on aircraft ranging from 1 to 3 kilogrammes. The lightweight design supports improved climb rate, extended flight time and enhanced flight envelope performance compared to heavier servo alternatives.
• Can I use the S-U400 in marine or waterproof RC applications? — The standard S-U400 is not rated for waterproof or marine use. For waterproof applications, Futaba manufactures purpose-designed waterproof servo alternatives. However, the S-U400 functions reliably in typical RC aircraft and surface vehicles operated in dry conditions, including aerobatic flying where splash exposure remains minimal.

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 (Bulk 10 pcs) FUT05102679-3-B 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.