What is the difference between an AIO and a stack?

An AIO puts the flight controller and the four motor drivers on one circuit board. A stack keeps them on two boards bolted together and joined by a connector. The electronics do the same job either way — the flight controller behaves identically, the firmware is the same and so is every setup step. What changes is size and weight, which extra features fit on the board, and what a failure costs to put right.

What does an AIO flight controller give up?

Usually three things, because the ESC occupies board area that would otherwise hold them. An on-board compass is commonly dropped, which also means ArduPilot cannot automatically work out an external compass's orientation, so you set it by hand. An analogue OSD chip is often dropped, since these boards assume a digital video system. And the 5 V supply is typically smaller, which matters if you plan to power several peripherals from it. Repairs are also all-or-nothing: a damaged motor channel means replacing the whole board.

Is an AIO less reliable than a stack?

Not inherently, and in one respect it is better: there is no board-to-board connector to seat wrongly or shake loose, and that connector is a real source of trouble on a stack because it carries battery voltage alongside signals. What an AIO concentrates is the consequence of a failure. On a stack a dead motor channel means a new ESC; on an AIO it means a new everything.

Do AIO boards run hotter?

The ESC section does the same work either way, but on an AIO it is sitting directly underneath the flight controller rather than on a board of its own with air between them. Ventilation matters more as a result: do not bury the board in foam, do not tape over the power transistors, and do not run a wiring loom across them. A current rating always assumes the board can shed its heat.

Which should I choose for a first build?

A stack, for most people. Not because it flies better — it does not — but because it is more forgiving of the mistakes a first build contains. A wrong ESC choice or a damaged motor channel replaces one board rather than both, the fuller feature set means fewer surprises, and a larger 5 V supply leaves room for the peripherals you decide to add later. Choose an AIO when size or weight is genuinely the constraint.

When would I use separate ESCs instead of a 4-in-1?

On larger aircraft, roughly seven inches and up. Each ESC mounts on its arm beside the motor, in clean airflow rather than inside the body, motor wires stay short, and a failure replaces one inexpensive part instead of a four-channel board. The cost is a great deal more wiring and many more soldered joints, plus the loss of the single shared current sensor a 4-in-1 provides. Below about seven inches it is rare.

AIO or a Stack?

Every multirotor needs the same two things: a flight controller to work out what the aircraft should do, and four motor drivers to do it. The question is how many circuit boards they live on, and it is one of the first decisions a build forces on you.

The short version: the flight controller behaves identically either way. Same firmware, same parameters, same wiring to a receiver or GPS, same setup steps. What changes is size, weight, which extra features fit, and what a failure costs to put right.

The three arrangements

AIO, stack and separate ESCs compared — what each arrangement trades

AIO — "all in one". Flight controller and four motor drivers on one board, one part number. The smallest and lightest option, with nothing between the two halves to come loose.

Stack — two boards, bolted together on the same mounting pattern and joined by a short cable. The usual arrangement, and the most flexible.

Separate ESCs — one ESC per motor, mounted out on the arms. Mostly seen on larger aircraft.

What an AIO gives up

The ESC occupies board area that would otherwise hold something else, so features get dropped. Which ones varies by board — check the manual for the one you are considering — but three are common enough to plan around.

The compass, and a consequence

Many AIO boards have no on-board compass, where a comparable standalone flight controller does.

To be fair about the cause: this is mostly a board area effect rather than an AIO one. Plenty of small standalone flight controllers leave the compass out too. But an AIO spends a large part of its area on the ESC, so it runs into the limit sooner — which is why the same manufacturer's AIO often lacks a compass its standalone board has.

For GPS flight you then need an external compass, which is on the GPS module most builds already use — and is a better compass anyway, because it sits on a mast away from the power wiring rather than centimetres from it.

But there is a second effect that catches people out. ArduPilot's automatic compass orientation detection stops working. It deduces an external compass's rotation by comparing it against a working internal one; with no internal compass there is nothing to compare against, so the orientation has to be set by hand. External Compass Orientation covers how.

Analogue OSD

AIO boards often omit the analogue OSD chip, so an analogue video feed gets no overlay. They assume a digital video system, with the OSD drawn over MSP DisplayPort instead.

If you fly analogue and want an OSD, check for the chip before buying.

5 V supply current

The 5 V supply on an AIO is typically smaller than on a comparable standalone board. Enough for a receiver, a GPS and a sensor or two, but worth adding up if you plan to hang much off it — an HD video system, a companion computer, several servos.

The number is in each board's manual. It is the specification most often discovered too late.

What a stack gives up

Being fair about it:

Size and weight. Two boards, standoffs and a connector are taller and heavier than one board.

A connector that has to be right. The cable between flight controller and ESC carries battery voltage on one pin and low-voltage signals on the others, and the pin order is not standardised between brands. Mating a mismatched cable puts battery voltage onto a signal pin and destroys the flight controller the moment you connect the battery. Boards sold as a stack come with the right cable; mixing brands means checking both pinouts and making one.

It is also one more thing to vibrate loose on a hard landing.

Heat

The ESC section does the same work in either arrangement. On an AIO it does it directly underneath the flight controller, rather than on its own board with air between.

So ventilation matters more:

Do not bury the board in foam or wrap it in tape.
Do not run a wiring loom across the power transistors.
Leave the ESC side of the board exposed to moving air.

A current rating always assumes the board can shed its heat. An AIO in a sealed cinewhoop body is not in the conditions its rating was measured in.

Repairs

This is the difference with real money attached.

A dead motor channel is the common ESC failure — a desoldered motor wire touching its neighbour, a prop strike stalling a motor, a crash.

On a stack: replace the ESC. The flight controller, and everything soldered to it, stays.
On an AIO: replace the board. Flight controller and ESC together.

That is not an argument against AIOs, but it belongs in the sums. On a small, light build the size saving may well be worth it; on a build carrying something expensive, the ability to replace one half is worth more.

Separate ESCs

Worth knowing about even though most builds will not use them.

On aircraft around seven inches and up, four individual ESCs mounted on the arms make sense:

Each sits next to its motor in clean airflow, not inside a hot body.
Motor wires stay short, which reduces electrical noise.
A failure replaces one inexpensive part.
High-current builds are easier to wire with thick leads going four separate ways.

The costs are real: far more wiring, many more soldered joints, four separate signal runs, and the loss of the single shared current sensor that a 4-in-1 gives you — so battery current monitoring needs a separate sensor.

Below about seven inches, a 4-in-1 wins on almost every count.

So which?

Choose a stack if:

It is your first build. Mistakes cost one board, not two.
You want the fuller feature set — on-board compass, analogue OSD, a larger 5 V supply.
You want to choose the ESC's current rating independently of the processor.
You expect to change one half later.

Choose an AIO if:

Size or weight is genuinely the constraint — a small frame, a cinewhoop, a sub-250 g build.
You are flying digital video, so the missing analogue OSD costs nothing.
You are using an external GPS and compass anyway.
You would rather have one fewer connector than one fewer shared failure.

Choose separate ESCs if:

The aircraft is seven inches or larger, or heavy-lift.
You want failures to be cheap and local.
You are comfortable with the extra wiring.

Compare the actual boards, not the categories

The differences above are tendencies, not rules. Some AIOs keep the compass; some stacks have a small 5 V supply. Before buying, check these four numbers in the manual: 5 V current, ESC continuous current, on-board compass or not, analogue OSD or not. They settle most of the decision.

Our boards, as an example

	Layout	Compass	Analogue OSD
H743 V2 + 4-in-1 ESC	stack, 30.5 × 30.5	on board	yes
H743 AIO	AIO, 25.5 × 25.5	external only	no
F405 V2 + 4-in-1 ESC	stack, 30.5 × 30.5	external only	yes
F405 Mini	stack, 20 × 20	external only	yes
NxtPX4 V2	stack, 20 × 20	external only	no

That table also makes the point above: the H743 V2 is the only one of these with a compass on board, and it is the physically largest. Board area is the real constraint, and an AIO spends a lot of it on the ESC.

The exact BEC and ESC current figures are in each manual, because those are the numbers worth checking rather than remembering.

Easily confused points

The flight controller is the same either way. An AIO is not a cut-down processor; it is the same class of board with the ESC added and some peripherals removed.

"AIO" says nothing about the ESC's quality. Check its current rating and firmware like any other ESC.

A missing on-board compass is not a problem in itself — an external one is better. It is the loss of automatic orientation detection that costs you a step.

The 8-pin stack connector is not a standard. Check pinouts before mating two brands.

Current ratings assume ventilation. They are not a promise in a sealed body.

ESC Firmware Explained — the other half of the electronics decision
MicoAir H743 AIO — User Manual
MicoAir H743 V2 — User Manual
External Compass Orientation — including the AIO case
ArduPilot Basic Configuration
Configure ESC Parameters

Written and maintained by the Robofusion engineering team.

The three arrangements​

What an AIO gives up​

The compass, and a consequence​

Analogue OSD​

5 V supply current​

What a stack gives up​

Heat​

Repairs​

Separate ESCs​

So which?​

Our boards, as an example​

Easily confused points​

Related guides​