Helicopter Configuration

This section contains topics related to helicopter configuration and tuning.

Note

Helicopters are less well-supported on than other types of vehicles. For example, PX4 does not support helicopters with coaxial or dual rotor types, and features such as RPM governor and autorotation. We would welcome your contribution of new features, new frame configurations, or other improvements.

Supported Configurations

Supported helicopter configurations:

• Single main rotor with swash-plate controlled by up to 4 swash-plate servos and a mechanically uncoupled tail rotor driven by an ESC.

Note

Mechanically coupled tails controlled by a servo can be flown by mapping the tail servo to the tail motor output and setting an adequate range and disarmed value for the servo. But the system currently assumes it's a separate motor.

Supported flight opertaion:

• Same as a multicopter. At the time of writing no autonomous/guided 3D flying with negative thrust is possible.

Setup

To setup and configure a helicopter:

1. Select the helicopter Airframe in QGroundControl

2. Configure helicopter actuator geometry in Vehicle Setup > Actuators.

   Note

   Actuator setup and testing is covered for most frames in Actuators. While that is referenced below, this is the main topic for helicopter setup information.

   The geometry for a Generic Helicopter - with Tail ESC is shown below.

   

   The motors have no configurable geometry:

   • Rotor (Motor 1): The main rotor
   • Yaw tail motor (Motor 2): The tail rotor

   Swash plate servos: 3 | 4

   For each servo set:

   • Angle: Clockwise angle in degree on the swash plate circle at which the servo arm is attached starting from 0 pointing forwards. Example for a typical setup where three servos are controlling the swash plate equally distributed over the circle (360° / 3 =) 120° apart each which results in the angles:

     #	Angle
     Servo 1	60°
     Servo 2	180°
     Servo 3	300°

     

   • Arm Length (relative to each other): Radius from the swash plate center (top view). A shorter arm means the same servo motion moves the plate more. This allows the autopilot to compensate.

   • Trim: Offset individual servo positions. This is only needed in rare case when the swash plate is not level even though all servos are centered.

   Additional settings:

   • Yaw compensation scale based on collective pitch: How much yaw is feed forward compensated based on the current collective pitch.
   • Main rotor turns counter-clockwise: Disabled (clockwise rotation) | Enabled
   • Throttle spoolup time: Set value (in seconds) greater than the achievable minimum motor spool up time. A larger value may improve user experience.

3. Remove the rotor blades and propellers

4. Assign motors and servos to outputs and test (also in Actuator configuration):

   1. Assign the motors and servos to the outputs.
   2. Power the vehicle with a battery and use the actuator testing sliders to validate correct servo and motor assignment and direction.

5. Using an RC in Acro mode, verify the correct movement of the swash-plate. With most airframes you need to see the following:

   • Moving the roll stick to the right should tilt the swash-plate to the right.
   • Moving the pitch stick forward should tilt the swash-plate forward.

   In case your airframe requires any phase lag angle offset this can simply be added to all swash-plate servo angles. Refer to the manufacturer's documentation for your airframe.

6. Arm the vehicle and check the main rotor spins up slowly. Adjust the throttle spoolup time as needed using the parameter COM_SPOOLUP_TIME. You can also adjust the throttle curve with the parameters CA_HELI_THR_Cx. The default is constant, maximum throttle (suitable for most setups).

7. Disarm again and power off.

8. Put the rotor blades on and power the vehicle.

9. Configure the collective pitch curve using the parameters CA_HELI_PITCH_Cx. Set the minimum and maximum according to the minimum and maximum blade angles you want. Make sure the minimum is low enough so the vehicle can still descend. Instead start off with a too low value. The default is slightly negative for that reason and should be a good starting point.

Tuning

After completing the previous steps you are ready to arm with blades mounted.

First tune the rate controller and yaw compensation as shown in the following sections (these are helicopter-specific).

Attitude, velocity, and position controller tuning is then performed in the same as for multicopters.

Note that autotuning is not supported/tested (at time of writing).

Yaw Compensation

Since the yaw torque compensation is crucial for a stable helicopter hover a rough configuration of it needs to be done first. For accurate tuning this chapter can be revisited once the rate controller is working as expected.

Most importantly set the rotation direction of your main rotor which is by default clockwise when seen from above the airframe. In case yours turns counter-clockwise set CA_HELI_YAW_CCW to 1.

There are two parameters to compensate yaw for the main rotor's collective and throttle: CA_HELI_YAW_CP_S CA_HELI_YAW_TH_S

A negative value is needed when positive thrust of the tail rotor rotates the vehicle opposite to the main rotor turn direction.

Rate Controller

The rate controller should be tuned in Acro mode, but can also be done in Stabilized mode if you cannot fly Acro mode.

1. Start off with disabled rate controller gains, and only a small feed forward:

   param set MC_ROLLRATE_P 0
   param set MC_ROLLRATE_I 0
   param set MC_ROLLRATE_D 0
   param set MC_ROLLRATE_FF 0.1
   param set MC_PITCHRATE_P 0
   param set MC_PITCHRATE_I 0
   param set MC_PITCHRATE_D 0
   param set MC_PITCHRATE_FF 0.1
   

2. Take off slowly and provide some roll and stick movements. Use the QGC tuning UI to check the response:

   

   Increase the roll and pitch feed forward gains MC_ROLLRATE_FF, MC_PITCHRATE_FF until the response reaches the setpoint when giving a step input.

3. Then enable the PID gains. Start off with following values:

   • MC_ROLLRATE_P, MC_PITCHRATE_P a quarter of the value you found to work well as the corresponding feed forward value in the previous step. P = FF / 4

   param set MC_ROLLRATE_I 0.2
   param set MC_PITCHRATE_I 0.2
   param set MC_ROLLRATE_D 0.001
   param set MC_PITCHRATE_D 0.001
   

   Then increase the P and D gains as needed until it tracks well. It is expected that the P gain is considerably smaller than the FF gain.