mavel

A position controller for multirotors

Parameters

Program Control

• control_rate (50.0): Update rate that mavel will run at
• control_frame ("map"): Frame ID to use on the output messages

Flight Settings & Limits

• throttle_min (0.0): Minimum throttle output that will be output
• throttle_mid (0.0): Hover throttle estimate (set low for initial tuning/testing)
  • Warning: setting this value too high may make your UAV take-off very quickly or not be able to perform a steady hover.
  • To tune:
    • Figure out your required hover throttle (take a reading of throttle position from manual flight).
    • Start with a value 5% less than this reading (i.e. if your reading was 40%, enter throttle_mid as 35%).
    • If take-off is too slow (e.g. > 5 seconds), increase this value in small increments (e.g. 2% steps).
  • If you cannot take a throttle reading for some reason:
    • Start with a value of 10-20%
    • Aim to see the UAV take-off after ~10 seconds.
    • Increment in mid-sized steps (e.g. 5% steps) until a 10 second take-off is achieved.
    • Decrease increment steps to small increments (e.g. 2%) until a successful takeoff is achieved.
  • Note: Most UAVs should have throttle_mid set in the range of 30-50%. If your UAV is outside of this range, it is likely over- or under-powered.
• throttle_max (0.9): Maximum throttle output that will be output
• tilt_max (0.39): Maximum attitude rotation from vertical (in radians)
• failsafe_land_vel (-0.2): Emergency landing velocity for soft failsafe (must be negative)
• failsafe_output_fatal (false): Enables all-low output if hard failsafe occurs (default is to disable all outputs)
• allow_timeout_position (false): Allows fallback to the last position received if a timeout occurs on the position/trajectory reference (can be abused to allow once-off position goals to be sent)

Data Stream Rates

Data stream minimum rates define the period of time that mavel will allow before declaring an input timeout. Default vaules for each stream are shown below:

• min_rate/state/mav_state (0.5)
• min_rate/state/odometry (20.0)
• min_rate/reference/trajectory (20.0)
• min_rate/reference/triplet (20.0)
• min_rate/reference/position (5.0)
• min_rate/reference/velocity (20.0)
• min_rate/reference/acceleration (40.0)

Controller Dynamic Reconfigure

Setting the PID controller parameters is done using Dynamic Reconfigure. These params can be loaded in using a params file (see launch folder for example)

Inputs

State References

• ~/reference/odom (nav_msgs/Odometry): Current odometry state
• ~/reference/state (mavros_msgs/State): Current UAV status (for armed/disarm flag)

Setpoint References

The following setpoint reference inputs are processed in reverse order. If mavel is presented with a higher-level input, it will switch over to that as the current reference instead. Specifically, if a pose is setpoint is being tracked, and a twist reference is provided, the twist will be used instead.

1. ~/reference/path (nav_msgs/Path): Path input used for a trajectory reference
2. ~/reference/traj (nav_msgs/Odometry): Odometry input used for trajectory reference (with orientation tracking)
3. ~/reference/triplet (mavros_msgs/PositionTarget): Linear triplet input used for trajectory, position, or velocity reference (with orientation or yaw rate tracking )
4. ~/reference/pose (geometry_msgs/PoseStamped): Pose used for position reference input (with orientation tracking)
5. ~/reference/twist (geometry_msgs/TwistStamped): Twist used for velocity reference input (with yaw rate tracking)
6. ~/reference/accel (geometry_msgs/AccelStamped): Acceleration used for acceleration reference input (with yaw acceleration tracking)

Outputs

Attitude Command

• ~/attitude (mavros_msgs/AttitudeTarget): The calculated attitude and throttle command

Control Feedback

• ~/feedback/pose (geometry_msgs/PoseStamped): The currently tracked pose reference
• ~/feedback/twist (geometry_msgs/TwistStamped): The currently tracked twist reference
• ~/feedback/accel_norm (geometry_msgs/AccelStamped): The currently tracked normalized acceleration reference