How to read a step response in Blackbox
A step response plot shows how fast and how cleanly your quad’s gyro follows a sudden stick input. The gyro line is drawn against the setpoint, normalised so that a perfect response settles at 1.0. You read three numbers from it: rise time (how quickly it gets there), overshoot (how far past 1.0 it goes) and settling time (how long until it stays at 1.0). For roll and pitch, an overshoot of about 5 to 10% with a short settling time is a good target.
What does a step response plot show?
You push the stick quickly. The setpoint jumps. The quad’s gyro follows, a little late. The plot takes many of these moves from a blackbox log, works out how the gyro responds to the setpoint and scales the result so the final value is 1.0.
- Vertical axis: the response, 1.0 meaning the gyro has matched the setpoint.
- Horizontal axis: time after the input, usually in milliseconds.
- Peak: the highest point of the curve. A peak of 1.0 means no overshoot.
It is an average over many moves, which makes it far less noisy than looking at one flip in the raw trace.
Rise time, overshoot and settling time
| Measure | What it is | Roll and pitch target |
|---|---|---|
| Rise time | Time to reach most of the way to 1.0 | As short as the quad allows without overshoot or noise growing |
| Overshoot | How far the peak goes above 1.0, in % | About 5 to 10% (peak about 1.0 to 1.1) |
| Settling time | Time until the curve stays near 1.0 | Short, with no ringing |
These are guides. They depend on your feel, which is personal: some pilots like a sharper response with a little more overshoot, others a softer one with less. Compare against your own earlier logs more than against a number from someone else’s quad. A peak below 1.0 means the response is overdamped, which usually means D is too high for the P.
How do I read the shapes?
| Shape | Likely cause | What to change |
|---|---|---|
| Overshoot above about 15% with ringing after the peak | P too high, or D too low | More D, or less P |
| Slow rise, soft peak at or below 1.0 | P too low, or D too high | More P, or less D |
| Reaches target on time, then creeps slowly up or down to 1.0 | I-term or feedforward | See below |
| Clean peak of 5 to 10% and a quick settle | Close to a balanced tune | Leave it |
Overshoot with oscillation
If the curve shoots past 1.0 and rings around it, the controller is pushing harder than the damping can absorb. That means too much P or not enough D. Raising D warms the motors, so after any D change arm on the ground, hover for about 20 seconds, land and touch the motors. The main PID tuning guide covers the P:D balance.
Slow and soft
A curve that climbs slowly and never overshoots means the quad is under-driven. P is too low, or D is holding it back. Raise P in a small step.
A slow drift to the target
If the curve gets most of the way, then takes a long time to close the last bit, look at the I-term and at feedforward. I-term closes slow errors, and feedforward drives the response from stick speed. The feedforward, I-term and TPA guide explains each.
Why does a full-stick snap show more overshoot?
Feedforward pushes the motors in response to how fast the stick moves. A full-stick snap is as fast as a stick can move, so feedforward contributes a lot of the overshoot in that move. The same quad flown with smaller, slower stick inputs overshoots less. The overshoot on a full-stick snap is therefore not purely a P:D problem.
Don’t chase that number down to the 5 to 10% band. If the overshoot is high but the curve settles quickly with no ringing, that is mostly feedforward and stick speed. Add damping when the settling is slow or the curve rings.
Roll against pitch
Pitch often needs a little more D than roll, because most frames have more inertia on pitch. The factory defaults reflect this: roll P 45 and D 30, pitch P 47 and D 34. Read each axis on its own and do not copy a change from one axis to the other.
Yaw tolerates more overshoot
Yaw is slower and less critical than roll and pitch. Yaw overshoot above the 5 to 10% roll and pitch target is normal, and yaw D defaults to 0 in every version. FPV PID Tune treats yaw overshoot up to 30% as inside what yaw tolerates, and leaves yaw alone unless it is clearly off or settling is very slow.
How many snaps do I need?
About 10 per axis, each with a short pause around it. Fewer than that, and the average is too noisy to trust. Fly them cleanly: full stick, held until the quad has rolled all the way round, then let go. Crashed moves and moves with the motors at their limit give bad data, so leave them out.
Which tools show a step response?
- Blackbox Explorer, Betaflight’s log viewer, shows the raw traces and a spectrum view. It’s the place to check individual moves.
- PIDtoolbox and its ports draw the averaged step response from a log.
- FPV PID Tune’s graphs show the step response for roll, pitch and yaw in the browser, after you fly the test pack and plug in again.
Our PIDtoolbox alternative and tool comparison pages go through the differences. Any of them needs a log that records the setpoint and the gyro; see blackbox logging for tuning.
How FPV PID Tune handles it
The app reads your log in the browser and measures overshoot, rise time, settling time and latency for roll, pitch and yaw. It treats snaps at full stick as valid evidence, and judges them with their feedforward share in mind. An AI picks values from those measurements, a validator holds every change to small steps per round, and the app says “Tuned” after the fourth round.