Snap Relax¶
Pop tops, pinwheels and snaps all start the same way: roll, pitch and yaw slammed in together. The wing stalls and autorotates, and the aircraft rotates much faster than the stick asks for, often two to two and a half times the commanded roll rate. A rate gyro sees that as an error and pushes back. Without Snap Relax it can put opposite aileron in while you are still holding full stick, and the I-term it builds up fighting the rotation comes back as a bump when you centre the sticks. The same goes for the rudder if the aircraft yaws faster than the stick asks for.
Snap Relax spots that stick gesture and stops the gyro fighting the rotation you asked for.
How it works¶
- Detection. A snap is detected when the roll, pitch and yaw sticks all pass the Stick threshold within the Entry window of each other. A slower build-up of the same inputs, such as a rolling harrier, does not count.
- While it is on. On roll, pitch and yaw, P and D are reduced by Strength only where they push against the direction you snapped the stick in, and I stops building up against that direction. Anything that helps the rotation, and the stick feedforward (F and B), stay as they are. Yaw usually lags the stick in a snap, so the rudder feedback helps and is left alone; it is only relaxed when the aircraft yaws faster than you asked.
- Exit. When any of the three sticks drops below the threshold, full feedback comes back over the Fade-out time. Reversing the stick against the snap during the fade brings full feedback back at once, so the gyro helps you stop the rotation.
It works in every stabilized mode and needs no switch.
Settings¶
Per PID profile. In the Configurator they are in Profiles → PID Settings (Expert Mode). On the radio they are on PID Controller (Ethos) and Profile - Various (EdgeTX).
| Setting | CLI | Range | Default |
|---|---|---|---|
| Strength | snap_relax_strength |
0-100 % | 100 |
| Stick threshold | snap_relax_threshold |
20-100 % | 60 |
| Entry window | snap_relax_window |
0-1000 ms | 400 |
| Fade-out | snap_relax_hold |
0-1000 ms | 350 |
Strength 0 turns it off.
Tuning¶
- The gyro still fights the entry: lower the stick threshold or widen the entry window, so the snap is caught for the way you put the sticks in.
- It triggers when you don't want it to: raise the threshold or narrow the window.
- The exit is sloppy, or the rotation carries on too long: shorten the fade-out. Lengthen it if the gyro snatches as you release.
To see it working, log with debug_mode = SNAP_RELAX (see the
CLI reference).