RC Servo Specifications: A Buyer’s Guide to Voltage, Torque and Interface

Compare RC servo specifications in a fixed order: exact model, motion type, supply, control signal, torque and speed conditions, mounting, output interface and supplied hardware. If the motion type or control interface is unresolved, stop before comparing headline torque.

This guide helps buyers screen an existing standard-servo replacement. It is not a wiring guide, flight-control setup or method for sizing an actuator from aircraft loads.

Servo model identification: match the documented motion type

Record the complete manufacturer model and every suffix. Then classify the documented function: limited-angle position control, continuous rotation speed control or another named actuator type.

Pololu’s FS5106B page provides a useful warning. It describes the FS5106B as a limited-range position-control servo and the FS5106R as a continuous-rotation speed-control servo, while stating that the two have identical dimensions and the same motor and gear reduction. A matching case therefore does not prove matching motion.

Use hold when the exact suffix or motion type is unknown. Do not ask torque to resolve an identity problem.

Read RC servo specifications at their stated conditions

The FS5106B specification page lists 4.8 kg·cm stall torque and 0.13 s/60° at 4.8 V, and 6 kg·cm and 0.11 s/60° at 6 V. These values belong to the named model and conditions; they are not a drone recommendation.

Field	Value to preserve	Do not convert it into
Stall torque	Rating type + voltage	A continuous-load recommendation
Speed	Time/angle + voltage + stated condition	Loaded motion in the buyer’s installation
Dimensions	Full drawing/reference	Proof of motion or mounting compatibility

Do not calculate a permitted continuous load from stall torque. Obtain the manufacturer limits and responsible application review.

Servo supply voltage vs signal voltage: keep them separate

Use three fields: power supply requirements, control-signal requirements and documented connector/pin assignment. The FS5106B page says the named servo can work with 3.3 V and 5 V control signals; that does not say a 3.3 V power supply is acceptable.

A familiar three-wire lead is not permission to guess the pinout. If the exact model’s connection document is missing, record hold for documentation. This article does not provide an improvised connection test.

Power, command and mechanical interfaces are separate checks. This is not a wiring diagram.

Read PWM servo specifications before interpreting “digital”

“Digital” can describe internal control behaviour; it does not by itself identify the external interface. The original Pololu servo-interface article treats pulse voltage, pulse width and pulse period as distinct parameters. Use the exact model documentation to identify the supported command signal.

Record one of: documented pulse interface, documented serial bus, another named interface or unknown. Unknown is not equivalent to PWM, and a change of control architecture requires a technical owner.

Check servo horn compatibility and mounting interfaces

Compare the mounting-hole pattern, output-shaft position, body envelope, lead exit and clearance against the accepted reference. Case width alone is insufficient.

For the horn, record the manufacturer’s output/spline reference, fastening method and supported horn part. Then state whether the quote includes the body, horn set and hardware. “Standard size” and “metal gear” do not answer those questions.

Use the package-contents guide to compare a body-only offer with a complete replacement scope.

RC servo specifications: a comparison worksheet

Field	Existing accepted record	Quoted item	Status
Exact model/suffix	Record	Record independently	Hold if different/unknown
Motion type	Position/continuous/other	Manufacturer-documented	Must agree with requirement
Supply	Range and conditions	Range and conditions	Technical review if different
Control	Exact interface	Exact interface	Hold if inferred
Torque/speed	Definition, voltage, condition	Same comparison basis	Open if conditions differ
Mount/output	Accepted drawing and horn	Drawing and horn reference	Hold if any interface open
Contents	Required scope	Included/excluded	Commercial scope match

A higher stall-torque number cannot close an unresolved motion, control or mounting question.

What to request when the documentation is incomplete

• Current datasheet and exact model/suffix
• Mechanical drawing and output/horn reference
• Supply and control-interface documentation
• Torque/speed definitions and their conditions
• Included accessories and hardware
• Named application limits or technical review path

If the seller cannot document a required field, leave it open and name the person who must resolve it. Avoid turning “Will it work on my drone?” into an unsupported sales yes/no answer.

Plan the sample without turning procurement into testing improvisation

A sample can confirm identity, supplied contents and specified dimensional observations. Functional or load evaluation needs a qualified plan and manufacturer guidance. Do not energize, stall or back-drive an unknown servo as a receiving shortcut.

Record the sample’s exact reference and change status. Use the sample-request guide to prevent one sample result from becoming blanket approval of later revisions.

Common questions

Does “digital servo” mean serial-bus control?

No. Use the exact model’s interface documentation; the label alone does not establish pulse or serial-bus control.

Does servo stall torque describe a continuous load?

No. It is a named rating condition, not a continuous-use recommendation. Keep voltage and rating definition attached.

Can servos with identical dimensions be substituted?

No general conclusion follows. FS5106B and FS5106R are a documented example of identical dimensions with different motion functions.

Is a robotics servo automatically suitable for a drone?

No. A catalog category is not approval for a specific aircraft or function. Use the responsible manufacturer’s or technical party’s acceptance process.

Request the existing model clearly

Send the exact model/suffix, motion type, required horn, quantity and comparison worksheet. If the reference is uncertain, start with the part-number guide. Mark alternatives separately from a same-reference replacement.

Sources and scope

Sources checked on 22 October 2026: Pololu’s FS5106B product/specification pages and the original Pololu servo-interface article. The model is a specification-reading example only; DroneNook does not represent it as approved for any aircraft.