Servo Setup¶
Set each servo's pulse range, update rate, centre and direction, so the mixer can drive the swashplate accurately. Do this before the mixer setup. All settings are on the Servos tab.
Servos unplugged for step 1
A servo driven at the wrong update rate can be damaged within seconds, and a narrow-band tail servo driven with a 1520 µs centre slams into its end stop. Set the rate and centre before plugging the servos in.
1. Rate and centre -- servos unplugged¶
From the servo data sheets:
| Typical cyclic servo | Typical narrow-band tail servo | |
|---|---|---|
| Center | 1520 µs | 760 µs |
| Rate | 333 Hz | 560 Hz |
| Min / Max | -700 / +700 | -350 / +350 |
| Scale neg / pos | 500 / 500 | 250 / 250 |
Analogue servos must be set to 50 Hz. Click Save and Reboot -- the rate only changes after a reboot.
Servos on the same timer share a rate. If changing one servo's rate changes another's, they're on one timer -- see Remapping.
2. Plug in the servos and set directions¶
- Connect the servos and power them (battery or BEC -- USB doesn't power servos). Swashplate servos go on outputs 1-3 as shown in the diagram on the tab; the tail servo on output 4.
- Fit the servo arms as close to 90° to the servo as the splines allow.
- Enable servo override and move servo 1's slider to a positive angle.
- The arm must move up, towards the swashplate. If it moves down, tick Reverse.
- Repeat for servos 2 and 3.
The tail servo's direction is set on the Mixer tab, later.
3. Centre the arms¶
With all overrides at 0°, adjust each servo's Center until its arm is exactly level (90° to the linkage). A quick way: move the override slider until the arm is level, read the PWM Signal value, copy it into Center, then set the override back to 0.
The swashplate will be levelled with the linkages in the mixer setup; here, only the servo arms matter.
4. Calibrate the throw (recommended)¶
Servos -- even identical ones -- don't all move exactly the same angle for the same signal. Calibrating them makes the swashplate move evenly, and is needed for geometry correction.
- Set a servo's override to +30°.
- Measure the arm angle (an arm-angle gauge or an app on a phone held against the arm).
- Adjust Scale pos until the arm is at exactly 30°.
- Repeat at -30° with Scale neg.
- Repeat for each servo.
If all swashplate servos are calibrated and move in an arc (not linear servos), turn on Geo cor for all of them.
5. Travel limits (usually not needed)¶
With the helicopter assembled, override each servo to about ±80°. If an arm or ball link hits anything, reduce Min or Max until it clears.
Rotorflight also limits the blade pitch in the mixer, so with sensible mixer limits these servo limits rarely come into play.
Turn the servo override off when you're done -- it blocks arming.
Next: Mixer & Swashplate Setup.