MC Jerk-limited Type Trajectory

The Jerk-limited trajectory type provides smooth motion 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.

This trajectory type is always enabled in Mission mode. To enable it in Position mode set the parameter: MPC_POS_MODE=3.

:::note The jerk-limited type is not used by default in position mode. It may not be suitable for vehicles/use-cases that require a faster response - e.g. racer quads. :::

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".

Manual Mode

In manual position mode, the sticks are mapped to velocity where a full XY-stick deflection corresponds to MPC_VEL_MANUAL and a full Z-stick deflection corresponds to MPC_Z_VEL_MAX_UP (upward motion) or MPC_Z_VEL_MAX_DN (downward motion).

Constraints

XY-plane:

jMax: MPC_JERK_MAX
aMax: MPC_ACC_HOR_MAX

Z-axis:

jMax: MPC_JERK_MAX
aMax (upward motion): MPC_ACC_UP_MAX
aMax (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).