How the verdicts are reached

Every rule, and what it does when it cannot tell.

These 21 rules produce every compatibility verdict in the planner. This page is generated from the same rows the engine reads, so it cannot describe a rule that does not run or leave out one that does.

Four answers, not two

A rule returns one of four results. Compatible and incompatible are the obvious pair. A warning means the combination works at a cost worth knowing about, which is a real answer and not a hedge: a battery connector that needs re-soldering is not the same problem as a voltage an ESC cannot survive.

The fourth is unknown, and it is deliberate. If a rule needs a specification that neither product records, the honest answer is that we cannot tell. Reporting an unchecked pair as compatible would be the one failure worth avoiding above all others, so an unrecorded value never becomes a pass.

Blocks the build

These parts cannot be used together. There is no setting that fixes it.

One product per build slot
Stops two products filling the same slot
When it passes
These fill different slots.
When it fails
Both products fill the first part's slot.
When a specification is missing
Not enough recorded specification to judge this combination.
Complete drone boundary
One product already contains the other
Applies betweenComplete droneandFrame, Flight stack (FC + ESC), Flight controller, ESC, Motors, Video transmitter, FPV camera, Receiver, Propellers
When it passes
Not part of a complete drone.
When it fails
A complete drone already includes this internal component.
When a specification is missing
Not enough recorded specification to judge this combination.
AIO board replaces the stack
One product already contains the other
Applies betweenAIO board (FC + ESC)andFlight stack (FC + ESC), Flight controller, ESC
The whoop norm is FC+ESC on one board.
When it passes
Not part of an AIO board.
When it fails
An AIO board already contains the flight controller and ESC.
When a specification is missing
Not enough recorded specification to judge this combination.
Control protocol match
Two single values must be the same
Applies betweenRadioandReceiver, Complete drone, AIO board (FC + ESC)
RF link protocol, not the receiver-to-FC serial protocol.
When it passes
Both use the first part's control link protocol control protocol.
When it fails
the first part's control link protocol cannot bind to the second part's control link protocol.
When a specification is missing
The control protocol of one of these is not recorded yet.
3 worked examples check this rule on every build.
Control band match
Both sides may list several values; they need one in common
Applies betweenRadioandReceiver, Complete drone
ELRS exists at 2.4 GHz and 900 MHz; matching protocol is not sufficient.
When it passes
Both work on the value they share.
When it fails
the first part transmits on what the first lists and the second part listens on what the second lists. Same protocol, but they cannot bind.
When it works with a compromise
the first part works on what the first lists, the second part on what the second lists. The 900 MHz band comes in an 868 MHz and a 915 MHz version which do not bind to each other, and one of these does not say which it is. Check the listing before buying.
When a specification is missing
The band of one of these is not recorded yet.
11 worked examples check this rule on every build.
Receiver protocol supported by flight controller
One value must appear in the other side's list
Applies betweenReceiverandFlight controller, Flight stack (FC + ESC)
When it passes
The flight controller supports the first part's receiver output protocol.
When it fails
The flight controller does not list support for the first part's receiver output protocol.
When a specification is missing
Not enough recorded specification to judge this combination.
Propeller fits the motor shaft
Two single values must be the same
Applies betweenPropellersandMotors
The hub either goes onto the shaft or it does not, and nothing downstream recovers from getting it wrong. 13 of 19 motors and 15 of 22 propellers record the fitting; where either side is blank this returns unknown, and on the 5-inch race motors it usually is.
When it passes
Both are the first part's propeller mounting.
When it fails
This propeller is the first part's propeller mounting and the second part is the second part's propeller mounting.
When a specification is missing
The mount on one of these is not recorded yet.
3 worked examples check this rule on every build.
Video system match
One value must appear in the other side's list
Applies betweenVideo transmitter, AIO board (FC + ESC), Flight stack (FC + ESC), Complete droneandGoggles
Three-valued: natively received, via a goggle AV/HDMI input (warning), or not at all.
When it passes
the second part receives the first part's video system.
When it fails
the second part does not receive the first part's video system.
When it works with a compromise
the second part does not receive the first part's video system natively, but accepts it through its AV or HDMI input. Expect a little added latency.
When a specification is missing
Not enough recorded specification to judge this combination.
5 worked examples check this rule on every build.
Camera matches the video transmitter
Two single values must be the same
Applies betweenFPV cameraandVideo transmitter, AIO board (FC + ESC), Flight stack (FC + ESC)
Digital FPV encodes in the air unit; the camera is part of that system rather than a generic sensor.
When it passes
Both are the first part's video system.
When it fails
the first part's video system camera cannot feed the second part's video system transmitter. Digital systems pair a camera and transmitter from the same family.
When a specification is missing
Not enough recorded specification to judge this combination.
3 worked examples check this rule on every build.
Stack mounting pattern
Both sides may list several values; they need one in common
Applies betweenFlight stack (FC + ESC), Flight controller, ESC, AIO board (FC + ESC), Video transmitterandFrame
When it passes
The frame accepts the value they share stack.
When it fails
This board mounts what the first lists and the frame accepts what the second lists.
When a specification is missing
The mounting pattern of one of these is not recorded yet.
5 worked examples check this rule on every build.
Motor mounting pattern
One value must appear in the other side's list
Applies betweenMotorsandFrame
A set, not a single value: 16x16 and 16x19 share an axis so frames often take both.
When it passes
the first part's motor mounting pattern motor pattern fits this frame.
When it fails
the first part's motor mounting pattern motors do not fit this frame's arm pattern.
When a specification is missing
Not enough recorded specification to judge this combination.
2 worked examples check this rule on every build.
Battery voltage suits the aircraft
One number against another, or against a limit
Applies betweenBatteryandComplete drone
Over-volting the electronics inside a ready-built aircraft destroys them exactly as it destroys a loose ESC, and under-volting simply will not fly. A plug that fits is not permission.
When it passes
the first part's cell countS is what the second part takes.
When it fails
the second part takes the second part's cell countS, and this is the first part's cell countS pack.
When a specification is missing
Not enough recorded specification to judge this combination.
4 worked examples check this rule on every build.
Battery voltage within supported range
One number against another, or against a limit
Applies betweenBatteryandESC, Flight stack (FC + ESC), AIO board (FC + ESC), Video transmitter, Flight controller
Over-volting an ESC or AIO destroys it, and often burns. Hard stop.
When it passes
the first part's cell countS is inside the second part supported range.
When it fails
the first part's cell countS is outside the second part's minimum cell count–the second part's maximum cell countS range the second part accepts.
When a specification is missing
Not enough recorded specification to judge this combination.
3 worked examples check this rule on every build.
Motor KV suits the battery
A suggested range rather than a hard limit
Applies betweenMotorsandBattery
When it passes
the first part's motor kvKV suits the second part's cell countS setup.
When it fails
the first part's motor kvKV on the second part's cell countS commands about the commanded RPM. That is far past anything this class of motor survives, and it will burn the motor and usually the ESC with it.
When it works with a compromise
the first part's motor kvKV on the second part's cell countS is outside the usual range. It will fly, but expect heat or lost punch.
When a specification is missing
Not enough recorded specification to judge this combination.
10 worked examples check this rule on every build.
Charger supports the battery
One number against another, or against a limit
Applies betweenBatteryandCharger
When it passes
The charger handles the first part's cell countS.
When it fails
the first part's cell countS exceeds the charger's the limitS the limit it crosses.
When a specification is missing
Not enough recorded specification to judge this combination.
Propeller fits the frame
One number against another, or against a limit
Applies betweenPropellersandFrame, Complete drone
When it passes
the first part's propeller size" props fit this frame.
When it fails
the first part's propeller size" exceeds the frame's the limit" the limit it crosses.
When it works with a compromise
This frame is specified for the limit" propellers. the first part's propeller size" is the usual fit in this class and is commonly run, but check arm and standoff clearance.
When a specification is missing
Not enough recorded specification to judge this combination.
3 worked examples check this rule on every build.
Propeller suits the build class
A number must be one of an allowed set
Applies betweenPropellersandFrame
65 mm whoops take 31 mm props, 75 mm take 40 mm, 85 mm take 45 mm.
When it passes
the first part's propeller size" suits the second part's build class build.
When it fails
the second part's build class build takes the expected value propellers, not the first part's propeller size".
When a specification is missing
Not enough recorded specification to judge this combination.
2 worked examples check this rule on every build.

Works, with a compromise

The combination functions, at a cost worth knowing about before you buy.

Antenna connector match
Two single values must be the same
Applies betweenAntennasandVideo transmitter, Goggles
A connector is mechanical, but a pigtail adapter is a normal part of this hobby and often ships with the transmitter. Say the sockets differ and name the remedy; do not refuse the pair.
When it passes
Both use the first part's antenna connector.
When it fails
This antenna is the first part's antenna connector and the second part takes the second part's antenna connector. A pigtail adapter is needed, and it adds a little loss.
When a specification is missing
The connector on one of these is not recorded yet.
3 worked examples check this rule on every build.
Camera size fits frame
One value must appear in the other side's list
Applies betweenFPV cameraandFrame
Nano-to-micro brackets are stock items, so a mismatch is a warning with a named remedy.
When it passes
the first part's camera size camera fits this frame.
When it fails
This frame is built for the second part's accepted camera sizes. the first part's camera size camera needs an adapter bracket.
When it works with a compromise
This frame is built for the second part's accepted camera sizes. the first part's camera size camera fits with an adapter bracket, which is a stock item.
When a specification is missing
Not enough recorded specification to judge this combination.
Battery connector match
Two single values must be the same
Applies betweenBatteryandESC, Flight stack (FC + ESC), AIO board (FC + ESC), Complete drone
When it passes
Both use the first part's battery connector.
When it fails
the first part's battery connector does not match the second part's battery connector.
When it works with a compromise
the first part's battery connector does not match the second part's battery connector. Re-soldering or an adapter is needed.
When a specification is missing
Not enough recorded specification to judge this combination.
Take-off weight under 250 g
Sums a property across the whole build against a limit
Sub-250 g changes the regulatory category. Component sums understate take-off weight, hence the margin.
When it passes
Estimated take-off weight the total g, under the 250 g threshold.
When it fails
Estimated take-off weight the total g, over the 250 g threshold. a remedy, where one applies
When a specification is missing
the missing part of the selected parts have no recorded weight, so this build cannot be confirmed under 250 g.
6 worked examples check this rule on every build.

Where these come from

The thresholds and enumerated values these rules compare were taken from the sources listed with each guide, not invented. Where a figure had one source, or where two sources disagreed, the value is recorded as unconfirmed and the affected rule returns unknown rather than a verdict.

All guides and sources Open the planner

Four answers, not two

Blocks the build

One product per build slot

Complete drone boundary

AIO board replaces the stack

Control protocol match

Control band match

Receiver protocol supported by flight controller

Propeller fits the motor shaft

Video system match

Camera matches the video transmitter

Stack mounting pattern

Motor mounting pattern

Battery voltage suits the aircraft

Battery voltage within supported range

Motor KV suits the battery

Charger supports the battery

Propeller fits the frame

Propeller suits the build class

Works, with a compromise

Antenna connector match

Camera size fits frame

Battery connector match

Take-off weight under 250 g

Where these come from