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Smarter RoC/RoD acceleration limit #4448

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Jun 3, 2019
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Smarter RoC/RoD acceleration limit #4448

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37 changes: 24 additions & 13 deletions src/main/navigation/navigation_multicopter.c
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Original file line number Diff line number Diff line change
Expand Up @@ -75,14 +75,24 @@ static void updateAltitudeVelocityController_MC(timeDelta_t deltaMicros)

posControl.pids.pos[Z].output_constrained = targetVel;

// limit max vertical acceleration to 1/5G (~200 cm/s/s) if we are increasing RoC or RoD (only if vel is of the same sign)
// if we are decelerating - don't limit (allow better recovery from falling)
const bool isSameDirection = (signbit(targetVel) == signbit(posControl.desiredState.vel.z)) && (targetVel != 0) && (posControl.desiredState.vel.z != 0);
if (isSameDirection && (fabsf(targetVel) > fabsf(posControl.desiredState.vel.z))) {
const float maxVelDifference = US2S(deltaMicros) * (GRAVITY_CMSS / 5.0f);
// Limit max up/down acceleration target
const float smallVelChange = US2S(deltaMicros) * (GRAVITY_CMSS * 0.1f);
const float velTargetChange = targetVel - posControl.desiredState.vel.z;

if (velTargetChange <= -smallVelChange) {
// Large & Negative - acceleration is _down_. We can't reach more than -1G in any possible condition. Hard limit to 0.8G to stay safe
// This should be safe enough for stability since we only reduce throttle
const float maxVelDifference = US2S(deltaMicros) * (GRAVITY_CMSS * 0.8f);
posControl.desiredState.vel.z = constrainf(targetVel, posControl.desiredState.vel.z - maxVelDifference, posControl.desiredState.vel.z + maxVelDifference);
}
else if (velTargetChange >= smallVelChange) {
// Large and positive - acceleration is _up_. We are limited by thrust/weight ratio which is usually about 2:1 (hover around 50% throttle).
// T/W ratio = 2 means we are able to reach 1G acceleration in "UP" direction. Hard limit to 0.5G to be on a safe side and avoid abrupt throttle changes
const float maxVelDifference = US2S(deltaMicros) * (GRAVITY_CMSS * 0.5f);
posControl.desiredState.vel.z = constrainf(targetVel, posControl.desiredState.vel.z - maxVelDifference, posControl.desiredState.vel.z + maxVelDifference);
}
else {
// Small - desired acceleration is less than 0.1G. We should be safe setting velocity target directly - any platform should be able to satisfy this
posControl.desiredState.vel.z = targetVel;
}

Expand Down Expand Up @@ -174,8 +184,9 @@ void setupMulticopterAltitudeController(void)
motorConfig()->minthrottle + rcControlsConfig()->alt_hold_deadband + 10,
motorConfig()->maxthrottle - rcControlsConfig()->alt_hold_deadband - 10);

/* Force AH controller to initialize althold integral for pending takeoff on reset */
if (throttleStatus == THROTTLE_LOW) {
// Force AH controller to initialize althold integral for pending takeoff on reset
// Signal for that is low throttle _and_ low actual altitude
if (throttleStatus == THROTTLE_LOW && fabsf(navGetCurrentActualPositionAndVelocity()->pos.z) <= 50.0f) {
prepareForTakeoffOnReset = true;
}
}
Expand Down Expand Up @@ -491,7 +502,7 @@ static void updatePositionAccelController_MC(timeDelta_t deltaMicros, float maxA
if (STATE(NAV_CRUISE_BRAKING)) {
maxAccelChange = maxAccelChange * 2;
}
#endif
#endif

const float accelLimitXMin = constrainf(lastAccelTargetX - maxAccelChange, -accelLimitX, +accelLimitX);
const float accelLimitXMax = constrainf(lastAccelTargetX + maxAccelChange, -accelLimitX, +accelLimitX);
Expand All @@ -513,17 +524,17 @@ static void updatePositionAccelController_MC(timeDelta_t deltaMicros, float maxA
//Boost required accelerations
if (STATE(NAV_CRUISE_BRAKING_BOOST) && navConfig()->mc.braking_boost_factor > 0) {
const float rawBoostFactor = (float)navConfig()->mc.braking_boost_factor / 100.0f;

//Scale boost factor according to speed
const float boostFactor = constrainf(
scaleRangef(
posControl.actualState.velXY,
navConfig()->mc.braking_boost_speed_threshold,
navConfig()->general.max_manual_speed,
posControl.actualState.velXY,
navConfig()->mc.braking_boost_speed_threshold,
navConfig()->general.max_manual_speed,
0.0f,
rawBoostFactor
),
0.0f,
0.0f,
rawBoostFactor
);

Expand Down