Micro Servos for RC Airplanes: Sizes, Torque and How to Choose
Micro servos are the small servos (roughly 2 g to 17 g) used in foam park flyers, indoor planes, small gliders and EDF jets. The classic 9 g servo, with about 1.5–2 kg·cm of torque, handles most planes up to about 1 m span; sub-micro 2–5 g servos suit indoor models; and slim “wing servos” fit thin glider wings. Choose by the load on the control surface: its size, the plane’s speed and the throw, then pick metal gears and digital electronics where precision and durability matter.
By Kyle HilsonUpdated: October 20263 min read
Size classes
| Class | Weight | Typical torque | Use |
|---|---|---|---|
| Sub-micro / ultra-micro | 2–5 g | 0.2–0.8 kg·cm | Indoor and F3P planes |
| Micro (9 g class) | 8–12 g | 1.5–2.5 kg·cm | Park flyers up to ~1 m span |
| Mini / slim wing | 12–20 g | 2–5 kg·cm | Gliders, EDF jets, 1–1.5 m planes |
Typical ranges; check the maker’s spec at your voltage.
How to choose
The load on a servo depends on the size of the control surface, the speed of the plane, the throw angle and the linkage geometry. A large aileron on a fast plane needs much more torque than a small rudder on a slow foamy. As a rough rule, choose a servo with comfortably more torque than seems necessary, because a servo that’s working near its limit is slow, imprecise and wears quickly. Speed matters for 3D and aerobatics; for trainers and gliders, precision and centring are more important than speed. The general approach to sizing is explained in how to choose servos for an RC plane.
Features
- Analog vs digital: digital servos hold position more firmly and centre better, but use more current.
- Plastic vs metal gears: metal survives hard landings and flutter; plastic is lighter and cheaper.
- Coreless motors: smoother and quicker than basic motors.
- Linear servos: slide instead of rotate; used in ultra-light indoor planes.
- Voltage: check whether the servo is rated for 1S, 4.8–6 V or HV (high voltage).
Installation tips
- Centre the servo with the radio on before fitting the horn.
- Mount it firmly: in foam, glue in a cut-out or use a servo tray; avoid glue in the gears or case seams.
- Use stiff pushrods and short, straight linkages to avoid slop.
- Set end points so the servo doesn’t stall at full throw.
- Route extensions so they can’t tangle in moving parts.
Power
Several micro servos on a small BEC can cause brownouts when they all move at once, especially digital servos. Check the ESC’s BEC rating and consider a separate BEC on larger foam planes. Basics of how servos work are in the RC servo guide.
Signs of a failing servo
- Jitter or buzzing at rest.
- Surface doesn’t return to the same centre.
- Stripped feel or slipping under load.
- Gets hot after a flight.
- Slow or uneven movement.
Replace these servos before they fail in the air, especially on ailerons and elevator.
Cheap or branded?
Very cheap 9 g servos work for simple foamies but vary in centring and lifespan. On planes you care about, and especially on elevator and ailerons, branded or well-reviewed servos with metal gears are worth the extra cost.
Storage
Keep spare servos dry and in their bags so dust doesn’t get into the gears.
FAQ
What is a 9 g servo good for?
Most foam park flyers up to about 1 m span.
Digital or analog micro servos?
Digital for precision; analog is fine on simple planes.
Do I need metal gears?
On faster planes and main surfaces, yes.
Can I use car servos in planes?
Car servos are usually too heavy for small planes.
More on this topic: the complete RC Airplanes guide covers the basics behind this article.
About 20 years in RC. Mostly boats in the NAVIGA Mini Eco Expert class, with many self-made parts; also a King Motor Baja 5B, a home-built electric plane, home-built nitro planes he has flown, and an RC helicopter. More about SwellRC
