Jerk-limited Type Trajectory for Multicopters

The Jerk-limited trajectory type should be used when smooth motion is required in response to user stick input or mission changes (e.g.: for filming, mapping, cargo). It generates symmetric smooth S-curves where the jerk and acceleration limits are always guaranteed.

Enable this trajectory type using the following parameter settings: MPC_POS_MODE=3, MPC_AUTO_MODE=1.

The jerk-limited type is used by default on all airframes, in both auto and position modes. Setpoint Tuning (Trajectory Generator) also supports MC Slew-rate Trajectory Tuning for a faster (albeit "jerky") response.

Trajectory Generator

The graph below shows a typical jerk-limited profile with the following constraints:

  • jMax: maximum jerk
  • a0: initial acceleration
  • aMax: maximum acceleration
  • a3: final acceleration (always 0)
  • v0: initial velocity
  • vRef: desired velocity

The constraints jMax, aMax are configurable by the user via parameters and can be different in manual position control and auto mode.

The resulting velocity profile is often called "S-Curve".

Jerk-limited trajectory

Manual Mode

In manual position mode, the sticks are mapped to velocity where a full stick deflection corresponds to MPC_VEL_MANUAL.

Constraints

XY-plane:

Z-axis:

Auto Mode

In auto mode, the desired velocity is MPC_XY_CRUISE but this value is automatically adjusted depending on the distance to the next waypoint, the maximum possible velocity in the waypoint and the maximum desired acceleration and jerk.

Constraints

XY-plane:

Z-axis:

Distance to velocity gains when close to a waypoint:

© PX4 Dev Team. License: CC BY 4.0            Updated: 2019-10-14 01:58:41

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