Jerk-limited Type Trajectory for Multicopters
The Jerk-limited trajectory type provides smooth motion in autonomous flight e.g. for filming, mapping, cargo. It generates symmetric smooth S-curves where the jerk and acceleration limits are always guaranteed.
This trajectory type is always enabled in autonomous modes like Mission mode.
Trajectory Generator
The graph below shows a typical jerk-limited profile with the following constraints:
jMax: maximum jerka0: initial accelerationaMax: maximum accelerationa3: final acceleration (always 0)v0: initial velocityvRef: 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".
Manual Mode
In manual position and altitude mode, jerk limiting is applied only to the vertical axis. Full throttle stick deflection commands the maximum vertical velocity which is MPC_Z_VEL_MAX_UP upwards and MPC_Z_VEL_MAX_DN downwards.
Constraints
Z-axis
jMax: MPC_JERK_MAXaMax(upward motion): MPC_ACC_UP_MAXaMax(downward motion): MPC_ACC_DOWN_MAX
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. The vertical speed is defined by MPC_Z_V_AUTO_UP (upward motion) and MPC_Z_V_AUTO_DN (downward motion).
Constraints
XY-plane:
jMax: MPC_JERK_AUTOaMax: MPC_ACC_HOR
Z-axis:
jMax: MPC_JERK_AUTOaMax(upward motion): MPC_ACC_UP_MAXaMax(downward motion): MPC_ACC_DOWN_MAX
Distance to velocity gains when close to a waypoint: