Should I choose the 55A or the 70A AM32 ESC?

By airframe size and mounting. The 55A suits 3.5 to 10 inch aircraft and has both 30.5 x 30.5 mm and 20 x 20 mm mounting holes. The 70A suits 5 to 12 inch aircraft and is 30.5 x 30.5 mm only. Counter-intuitively the 55A has the lower MOSFET resistance at 0.75 milliohms against the 70A's 0.95 — the 70A is rated higher because its MOSFETs are in a metal package that sheds heat better, which is what limits sustained current.

Why do my motors run badly with a large low-KV motor on an AM32 ESC?

The firmware ships with a motor KV setting of 2220, which suits typical freestyle motors. Fit a large low-KV motor or a very high-KV small motor and that default no longer matches, so the ESC's timing behaviour is wrong for the motor and it may not reach the speed you expect. Set the motor KV value in an AM32 configurator to match the motors you actually fitted.

What is the difference between AM32 and Bluejay firmware?

They run on different hardware generations. Bluejay is open-source firmware for 8-bit ESCs, the same hardware that runs BLHeli_S. AM32 is open-source firmware for 32-bit ESCs, with more processing headroom and more configurable behaviour such as the motor KV setting. Both are configured through the same flight-controller passthrough and both support bidirectional DShot.

What should BATT_AMP_PERVLT be for a MicoAir AM32 ESC?

It depends on which one you have, because the two differ. The 55A outputs 12.75 mV per amp, which is about 78 amps per volt; the 70A outputs 10.2 mV per amp, which is about 98. Neither matches the 40.2 that MicoAir flight controllers ship with, so the default will under-report current. Use the calculated figure as a starting point and calibrate against a charger's mAh reading.

Can the AM32 ESC run in a sealed enclosure?

No. Both are rated at their full continuous current only with good airflow, and neither should be run in a sealed compartment. Sustained current is limited by how fast the board sheds heat, so an ESC with nowhere to put that heat will derate itself or fail.

MicoAir 4-in-1 AM32 ESC — User Manual

The AM32 ESCs are the 32-bit half of MicoAir's 4-in-1 line: more current, more headroom and more configurability than the 8-bit Bluejay boards, aimed at larger and longer-range aircraft.

Two models, both running AM32 firmware at 48 kHz PWM with DShot300/600 support.

MicoAir 70A 4-in-1 AM32 ESC

55A or 70A?

	55A	70A
Max continuous current	55 A × 4	70 A × 4
Battery	2–6S	2–6S
MOSFETs	40 V, 0.75 mΩ	40 V, 0.95 mΩ, metal package
Current-sensor output	12.75 mV/A	10.2 mV/A
Mounting	30.5 × 30.5 (Φ4) + 20 × 20 (Φ3)	30.5 × 30.5 mm (Φ4)
Board size	43.5 × 41 mm	43.5 × 42.5 mm
Weight	14 g	14.5 g
Suggested airframe	3.5–10 inch	5–12 inch

Shared by both: AM32 firmware (AM32_F4A_4IN1_F421_2.19), 48 kHz PWM, PWM / DShot300 / DShot600, and an SH1.0-8P connector.

The 55A has lower resistance than the 70A — so why is the 70A rated higher?

Because sustained current is limited by heat, not by resistance alone. The 55A's MOSFETs have the lower R_DS(on) at 0.75 mΩ, but the 70A's are in a metal package that moves heat off the die far more effectively. More heat out means more current in, even though each amp costs slightly more loss. Resistance tells you how much heat is produced; packaging tells you how much can be removed.

Choosing in practice:

55A — the more flexible board. It covers 3.5 to 10 inch, and it is the only one of the two with both hole patterns, so it fits 20 × 20 mm stacks as well as 30.5 × 30.5.
70A — for 5 to 12 inch aircraft, heavy lifters and long-range builds where sustained current matters more than a few grams or millimetres.

Both need airflow

The continuous ratings assume good heat dissipation. Neither should be run in a sealed compartment. An ESC with nowhere to put its heat will get hot, derate, and eventually fail — and the failure will be during the part of the flight that was drawing the most current.

Where to buy

Ships from Canada with free Canada-wide shipping:

MicoAir 70A 4-in-1 AM32 ESC
H743 V2 + AM32 flight stack — the H743 V2 with either the 55A or the 70A

MicoAir 55A 4-in-1 AM32 ESC

Connector pinout

Both models use the same SH1.0-8P connector, with the same pin order as the Bluejay boards:

The SH1.0-8P pinout of a MicoAir 4-in-1 ESC — Curr, NC, M4, M3, M2, M1, VBAT, GND

Pin	Function
Curr	Current-sensor output — 12.75 mV/A on the 55A, 10.2 mV/A on the 70A
NC	Not connected
M4 – M1	Motor signal inputs from the flight controller's outputs
VBAT	Raw battery voltage out — typically used to power the flight controller. A 6S pack puts about 22.2 V here
GND	Power ground

VBAT is battery voltage, not 5 V

It feeds the flight controller's own regulator. A receiver, GPS or camera connected to this pin will be destroyed.

MicoAir 70A AM32 ESC, top and bottom

Installing it

How a 4-in-1 ESC connects to the battery, the motors and the flight controller

Battery to the ESC — solder the leads or an XT60 to the + and − pads. Reversed polarity destroys the board instantly.
Fit the capacitor across the same pads. It absorbs the voltage spikes that switching motors put on the power rail; without it those spikes reach the flight controller and the video system.
Motors to the ESC — three wires each, to pads 1–4. Direction is set in software later, so wire order does not matter yet.
Ribbon to the flight controller using the SH1.0-8P cable.
Mount on soft grommets, to keep motor vibration out of the flight controller's gyro.

Props off for anything electrical

Remove the propellers before wiring, testing motors, checking direction or changing ESC settings.

Flight controller setup

Set the protocol to DShot300

AM32 accepts PWM, DShot300 and DShot600. DShot300 is the recommended setting — the balance point between bandwidth and reliability.

If the flight controller is left on a protocol the ESC does not expect, the motors will not respond at all on arming or motor test, with no error reported.

Set the motor KV

This one is specific to AM32 and easy to miss.

The firmware ships with a motor KV value of 2220, which suits a typical freestyle motor. That value feeds the ESC's timing behaviour — so if you have fitted a large low-KV motor or a small very-high-KV motor, the default no longer describes your hardware and the motor may not reach the speed you expect.

Set it to match the motors you actually fitted, in an AM32 configurator: Configuring ESC Parameters.

Set the current-sensor scaling

The two models differ, so check which one you have:

ESC	Sensor output	ArduPilot `BATT_AMP_PERVLT`
55A	12.75 mV/A	≈ 78
70A	10.2 mV/A	≈ 98

ArduPilot's BATT_AMP_PERVLT is expressed in amps per volt, so the figure is 1 ÷ (mV/A ÷ 1000).

The board default matches neither model

MicoAir's F405 V2 and H743 V2 ship with BATT_AMP_PERVLT = 40.2, which implies a sensor of about 24.9 mV/A — that is neither 12.75 nor 10.2. Leave the default in place and the reported current will be substantially lower than reality, which makes consumed-mAh and any current-based failsafe wrong in the direction that lets you fly on further than you should.

Treat the calculated figure as a starting point, then calibrate:

Fly a pack down, or run a known load.
Compare the mAh the flight controller reported with the mAh your charger puts back in.
Scale BATT_AMP_PERVLT by that ratio.
Repeat once to confirm.

AM32, Bluejay and the rest

Firmware	Hardware	Notes
BLHeli_S	8-bit	Long-standing stock firmware for this class. No bidirectional DShot.
Bluejay	8-bit	Open-source, same hardware and configurator as BLHeli_S. Adds 48 kHz PWM and bidirectional DShot.
BLHeli_32	32-bit	More capable, closed source, no longer developed.
AM32	32-bit	Open-source firmware for 32-bit ESCs — what these boards run. More headroom and more settings, including motor KV.

The practical split: Bluejay on our 8-bit boards covers small and mid-size quads very well; AM32 is the 32-bit path, with the extra current handling and the extra configurability that larger motors benefit from.

Easily confused points

The two models have different current sensors. 12.75 mV/A on the 55A, 10.2 mV/A on the 70A — and neither matches the flight controller's default. This is the single most likely thing to get wrong.

Lower resistance does not mean higher rating. Packaging and heat dissipation decide sustained current.

The KV setting is not decorative. AM32's default assumes a 2220 KV motor.

"Continuous current" assumes airflow. Not in a sealed compartment.

"No motors" is a protocol setting. DShot300 first.

A 4-in-1 is four ESCs. One channel can fail alone — if exactly one motor misbehaves, suspect that channel.

VBAT is not a 5 V rail.

Troubleshooting

Symptom	Where to look
No motors respond at all	ESC protocol not DShot300; ribbon not seated; no battery (USB does not power the ESC).
One motor does not spin	That channel — motor solder joints, the motor itself, or that one ESC.
Motors spin the wrong way	Reverse it in the ESC configurator, not by swapping wires.
Motor will not reach expected speed	Motor KV setting still at the 2220 default while a very different motor is fitted.
Current reads far too low	`BATT_AMP_PERVLT` left at the board default — see the scaling table above.
ESC gets very hot	Undersized for the build, or mounted with no airflow.
Noisy gyro, bars in the video	Missing capacitor, or the stack mounted hard to the frame instead of on grommets.

How to Configure Open-Source ESC Parameters — motor direction, KV, and firmware updates
MicoAir 4-in-1 Bluejay ESC — User Manual — the 8-bit boards
H743 V2 Flight Controller — User Manual
F405 V2 — Beginner ArduPilot Setup Guide

Written and maintained by the Robofusion engineering team.

55A or 70A?​

Where to buy​

Connector pinout​

Installing it​

Flight controller setup​

Set the protocol to DShot300​

Set the motor KV​

Set the current-sensor scaling​

AM32, Bluejay and the rest​

Easily confused points​

Troubleshooting​

Related guides​