Diagnostics
13 articlesSomething is wrong with the aircraft. Each article answers exactly one question.
Slow wobble on a big quad: PID too hot, or is your arm a spring?
On a heavy airframe, an over-gained control loop and a flexing frame produce the same slow wobble. Here is how to tell which one you have, and why no PID value fixes a spring.
Why did one motor stop mid-flight?
The quad drops out of the sky, then flies home as if nothing happened. That is desync — the ESC losing track of where the rotor is. Here is what it actually is, and how to prove it in a log.
Is it propwash, or is my tune bad?
One question separates them, and it is not what the shake looks like — it is when it happens. Clean air is the test.
Why do my motors get hot?
Heat is not a fault in its own right. It is the electrical energy your build failed to turn into thrust, and it tells you exactly where the waste is going.
Why do I lose GPS lock?
Almost every bad GPS is a good GPS being shouted down by your own aircraft. Find the noise source, not a new module.
Why does my quad drift in Angle mode?
"Drift" is at least three different faults, and one of them is not a fault at all. Work out which one you have before you calibrate anything.
Why does my quad flip on takeoff?
The flip of death is not a tuning problem, and it is not bad luck. It is a very short list of causes, and the direction it flipped tells you which one.
Why does my video break up?
Video breakup is an RF problem wearing a video costume. Three questions separate almost every case, and the answer is usually the antenna.
Why is my ESC beeping?
An ESC beeps by playing tones through the motor windings. Once you know that, the sound tells you which of half a dozen things is wrong — starting with whether it is the ESC beeping at all.
Why does my quadcopter shake?
Shaking is four completely different faults wearing the same costume. Identify which one you have in about a minute, then fix that one.
Why does my voltage sag under throttle?
Every LiPo sags. That is Ohm's law, not a fault. The only question worth asking is whether yours sags more than it should — and here is how to answer it.
Why does one motor behave differently?
One motor hotter, louder, or working harder than the other three is almost never the motor's fault. It is the flight controller correcting for something, and the pattern tells you what.
Why won't my quad arm?
Betaflight already knows why, and it will tell you in one word. Here is how to ask it, and what every answer means.
Flight Firmware
4 articlesBetaflight, iNAV, ArduPilot — how they differ, how they are built, and how to test changes without crashing.
Betaflight vs iNAV vs ArduPilot: which one, and why
Three firmwares, three completely different jobs. Choose by what the aircraft is for, not by what you already know.
How to test firmware changes without breaking an aircraft
A staged procedure for validating a firmware or tuning change — bench, SITL, HIL, tethered hover, real flight — where each rung is cheaper to be wrong on than the one above it.
What is HIL, and how is it different from SITL?
HIL puts the real flight controller board inside the simulation loop. It is closer to the truth, more work to set up, and it answers a narrower set of questions than most people expect.
What is SITL, and why should a pilot care?
SITL means running the real flight-controller firmware on a computer instead of on a flight controller. It is the cheapest way to be wrong.
Tuning
7 articlesPIDs, filters, rates and vibration, explained in terms of what you will actually feel in the air.
Is AutoTune safe on a 20 kg aircraft?
AutoTune works by deliberately walking an aircraft toward instability and stopping just before. On a 20 kg airframe, the margin between "just before" and "too late" is very thin, and very expensive.
Why a 5-inch racer tune destroys a 5 kg quad
Every default PID set you can flash was written for a 250 g aircraft. Here is what actually changes when the machine gets big, what it does to each term, and why nobody can hand you numbers.
Hover throttle is the number that decides everything
The throttle position you hover at is the cheapest diagnostic on the aircraft, and almost nobody reads it. It tells you whether the thing can be tuned, flown safely, or trusted to come home.
PID and filters in plain English
What P, I, D and feedforward actually respond to, what each one feels like when it is wrong, and why every filter you add is a loan against your control authority.
Rates: what each number actually does to the stick
Rates are not a tune. They are the mapping from your stick to a commanded rotation rate. Here is what each of the three knobs does, and why copying someone else's rates is pointless.
How to read a Blackbox log
The log is the only record of what your aircraft actually did. Four traces carry most of the diagnosis — here is what each one means and the order to read them in.
Tuning an aircraft whose weight changes
A sprayer that takes off at 38 kg and lands at 22 kg is two different aircraft. You cannot tune both, so you tune the one that would otherwise kill you — and it is not the one most people pick.
Autonomous Flight
3 articlesGPS, RTL, missions, geofences and failsafe — the parts of the stack the FPV world skips.
GPS Rescue and Return-to-Home, step by step
Return-to-home is a state machine, not a magic button. Here is what each phase does, what it requires to work, and the ways it kills aircraft.
What failsafe really does when the link drops
Failsafe is two systems, not one — the receiver and the flight controller — and if you only configured one of them, your aircraft will fly away.
Will a hexacopter survive a motor failure?
More motors is not the same thing as redundancy. Redundancy is thrust margin, and on a hexacopter it also depends on which motor died.
Building
3 articlesSoldering, wiring, capacitors, centre of gravity, and the checks that come before the first spin-up.
What to check before the first power-up
A new build is at its most fragile in the five seconds after you first plug a battery in. Here is the order to do things in, and why the order is the whole point.
How to spot a failing motor before it fails
Motors and bearings almost never die without warning. They give you weeks of it. Here is what a dying motor feels like, sounds like and logs like, and when to stop trusting it.
Where to put the capacitor (and why it matters)
Everybody tells you to add a capacitor. Almost nobody tells you what it does, where it has to go, or what it will not fix. Here is all three.