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Code Issues Releases Activity

OP-1352 cleaned up some code comments

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This commit is contained in:
Corvus Corax 2014-05-17 23:27:30 +02:00
parent 5544e9c984
commit 5153806289
1 changed files with 64 additions and 42 deletions
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106
flight/modules/FixedWingPathFollower/fixedwingpathfollower.c
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@ -406,14 +406,14 @@ static uint8_t updateFixedDesiredAttitude()
/**
* Compute speed error and course
*/
// missing sensors for airspeed-direction we have to assume within reasonable error
// that measured airspeed is always the component in forward pointing direction
// this vector is normalized
// missing sensors for airspeed-direction we have to assume within
// reasonable error that measured airspeed is actually the airspeed
// component in forward pointing direction
// airspeedVector is normalized
airspeedVector[0] = cos_lookup_deg(attitudeState.Yaw);
airspeedVector[1] = sin_lookup_deg(attitudeState.Yaw);
// Current ground speed projected in forward direction
// current ground speed projected in forward direction
groundspeedProjection = velocityState.North * airspeedVector[0] + velocityState.East * airspeedVector[1];
// note that airspeedStateBias is ( calibratedAirspeed - groundspeedProjection ) at the time of measurement,
@ -421,10 +421,13 @@ static uint8_t updateFixedDesiredAttitude()
// than airspeed and gps sensors alone
indicatedAirspeedState = groundspeedProjection + indicatedAirspeedStateBias;
// fluidMovement is a vector describing the aproximate movement vector in surrounding fluid (2d)
fluidMovement[0] = velocityState.North - (indicatedAirspeedState * airspeedVector[0]);
fluidMovement[1] = velocityState.East - (indicatedAirspeedState * airspeedVector[1]);
// fluidMovement is a vector describing the aproximate movement vector of
// the surrounding fluid in 2d space (aka wind vector)
fluidMovement[0] = velocityState.North - (indicatedAirspeedState * airspeedVector[0]);
fluidMovement[1] = velocityState.East - (indicatedAirspeedState * airspeedVector[1]);
// calculate the movement vector we need to fly to reach velocityDesired -
// taking fluidMovement into account
courseComponent[0] = velocityDesired.North - fluidMovement[0];
courseComponent[1] = velocityDesired.East - fluidMovement[1];
@ -432,11 +435,14 @@ static uint8_t updateFixedDesiredAttitude()
fixedwingpathfollowerSettings.HorizontalVelMin,
fixedwingpathfollowerSettings.HorizontalVelMax);
// if we could fly at arbitrary speeds, we'd just have to move into courseComponent and we'd be fine
// unfortunately we bound by min and max speed, so we need to calculate the correct course to meet
// at least the velocityDesired vector direction at our current speed
// if we could fly at arbitrary speeds, we'd just have to move towards the
// courseComponent vector as previously calculated and we'd be fine
// unfortunately however we are bound by min and max air speed limits, so
// we need to recalculate the correct course to meet at least the
// velocityDesired vector direction at our current speed
// this overwrites courseComponent
bool valid = correctCourse(courseComponent, (float *)&velocityDesired.North, fluidMovement, indicatedAirspeedDesired);
// Error condition: wind speed too high, we can't go where we want anymore
fixedwingpathfollowerStatus.Errors.Wind = 0;
if ((!valid) &&
@ -478,14 +484,15 @@ static uint8_t updateFixedDesiredAttitude()
/**
* Compute desired thrust command
*/
// compute saturated integral error thrust response. Make integral leaky for better performance. Approximately 30s time constant.
if (fixedwingpathfollowerSettings.PowerPI.Ki > 0) {
powerIntegral = boundf(powerIntegral + -descentspeedError * dT,
-fixedwingpathfollowerSettings.PowerPI.ILimit / fixedwingpathfollowerSettings.PowerPI.Ki,
fixedwingpathfollowerSettings.PowerPI.ILimit / fixedwingpathfollowerSettings.PowerPI.Ki
) * (1.0f - 1.0f / (1.0f + 30.0f / dT));
} else { powerIntegral = 0; }
} else {
powerIntegral = 0;
}
// Compute the cross feed from vertical speed to pitch, with saturation
float speedErrorToPowerCommandComponent = boundf(
@ -534,7 +541,6 @@ static uint8_t updateFixedDesiredAttitude()
/**
* Compute desired pitch command
*/
if (fixedwingpathfollowerSettings.SpeedPI.Ki > 0) {
// Integrate with saturation
airspeedErrorInt = boundf(airspeedErrorInt + airspeedError * dT,
@ -655,8 +661,6 @@ static void airspeedStateUpdatedCb(__attribute__((unused)) UAVObjEvent *ev)
// vector projection of groundspeed on airspeed vector to handle both forward and backwards movement
float groundspeedProjection = velocityState.North * airspeedVector[0] + velocityState.East * airspeedVector[1];
// warning - deliberately messed up airspeed sensor value to see if course calculation is coping with crappy sensor
// do not let this pass the review ;)
indicatedAirspeedStateBias = airspeedState.CalibratedAirspeed - groundspeedProjection;
// note - we do fly by Indicated Airspeed (== calibrated airspeed) however
// since airspeed is updated less often than groundspeed, we use sudden
@ -667,71 +671,83 @@ static void airspeedStateUpdatedCb(__attribute__((unused)) UAVObjEvent *ev)
/**
* Function to correct course C based on airspeed s, fluid movement F and desired movement vector V
* Function to calculate course vector C based on airspeed s, fluid movement F
* and desired movement vector V
* parameters in: V,F,s
* parameters out: C
* returns true if a valid solution could be found for V,F,s, false if not
* C will be set to a best effort attempt either way
*/
static bool correctCourse(float *C, float *V, float *F, float s)
{
// approach:
// let Sc be a circle around origin marking possible movement vectors
// of the craft with airspeed s
// let Vl be a line through the origin along movement vector V
// let Wl be a line parallel to Vl where for any point v on line Vl
// there is a point w on WL with w = v - F
// then any intersecting point between Sc and Wl is a course which
// results in a movement vector k*V
// if there is no intersection point, S is insufficient to compensate
// for F and we better fly in direction of V (thus having wind drift
// Approach:
// Let Sc be a circle around origin marking possible movement vectors
// of the craft with airspeed s (all possible options for C)
// Let Vl be a line through the origin along movement vector V where fr any
// point v on line Vl v = k * (V / |V|) = k' * V
// Let Wl be a line parallel to Vl where for any point v on line Vl exists
// a point w on WL with w = v - F
// Then any intersection between circle Sc and line Wl represents course
// vector which would result in a movement vector
// V' = k * ( V / |V|) = k' * V
// If there is no intersection point, S is insufficient to compensate
// for F and we can only try to fly in direction of V (thus having wind drift
// but at least making progress orthogonal to wind)
s = fabsf(s);
float f = sqrtf(F[0] * F[0] + F[1] * F[1]);
// normalize V
// normalize Cn=V/|V|, |V| must be >0
float v = sqrtf(V[0] * V[0] + V[1] * V[1]);
if (v < 1e-6f) {
// if we aren't supposed to move, turn into the wind (this allows hovering)
// if |V|=0, we aren't supposed to move, turn into the wind
// (this allows hovering)
C[0] = -F[0];
C[1] = -F[1];
return fabsf(f - s) < 1e-3f; // returns true if a hover is actually intended
// if desired airspeed matches fluidmovement a hover is actually
// intended so return true
return fabsf(f - s) < 1e-3f;
}
float Vn[2] = { V[0] / v, V[1] / v };
// project F on V
float fp = F[0] * Vn[0] + F[1] * Vn[1];
// find component of F orthogonal to V (distance between V and W)
// find component Fo of F that is orthogonal to V
// (which is exactly the distance between Vl and Wl)
float Fo[2] = { F[0] - (fp * Vn[0]), F[1] - (fp * Vn[1]) };
float fo2 = Fo[0] * Fo[0] + Fo[1] * Fo[1];
// find k where k * Vn = C - Fo
// S is the hypothenuse in any rectangular triangle formed by k * Vn and Fo
// so k^2 + fo^2 = s^2 (since |Vn|=1)
// |C|=s is the hypothenuse in any rectangular triangle formed by k * Vn and Fo
// so k^2 + fo^2 = s^2 (since |Vn|=1)
float k2 = s * s - fo2;
if (k2 <= -1e-3f) {
// there is no solution, we will be drifted off either way
// fallback: fly stupidly towards V and hope for the best
// fallback: fly stupidly in direction of V and hope for the best
C[0] = V[0];
C[1] = V[1];
return false;
} else if (k2 <= 1e-3f) {
// there is one solution: -Fo
// there is exactly one solution: -Fo
C[0] = -Fo[0];
C[1] = -Fo[1];
return true;
}
// now we have two possible solutions k positive and k negative
// which one is better?
// two criteria:
// 1. we MUST move in the right direction, if k leads to -v its invalid
// we have two possible solutions k positive and k negative as there are
// two intersection points between Wl and Sc
// which one is better? two criteria:
// 1. we MUST move in the right direction, if any k leads to -v its invalid
// 2. we should minimize the speed error
float k = sqrt(k2);
float C1[2] = { -k * Vn[0] - Fo[0], -k * Vn[1] - Fo[1] };
float C2[2] = { k *Vn[0] - Fo[0], k * Vn[1] - Fo[1] };
// project each solution on Vn to find length
// project C+F on Vn to find signed resulting movement vector length
float vp1 = (C1[0] + F[0]) * Vn[0] + (C1[1] + F[1]) * Vn[1];
float vp2 = (C2[0] + F[0]) * Vn[0] + (C2[1] + F[1]) * Vn[1];
if (vp1 >= 0.0f && fabsf(v - vp1) < fabsf(v - vp2)) {
// in this case the angle between course and resulting movement vector
// is greater than 90 degrees - so we actually fly backwards
C[0] = C1[0];
C[1] = C1[1];
return true;
@ -739,8 +755,14 @@ static bool correctCourse(float *C, float *V, float *F, float s)
C[0] = C2[0];
C[1] = C2[1];
if (vp2 >= 0.0f) {
// in this case the angle between course and movement vector is less than
// 90 degrees, but we do move in the right direction
return true;
} else {
// in this case we actually get driven in the opposite direction of V
// with both solutions for C
// this might be reached in headwind stronger than maximum allowed
// airspeed.
return false;
}
}