diff --git a/flight/modules/FixedWingPathFollower/fixedwingpathfollower.c b/flight/modules/FixedWingPathFollower/fixedwingpathfollower.c index 89e731fca..d664ee91e 100644 --- a/flight/modules/FixedWingPathFollower/fixedwingpathfollower.c +++ b/flight/modules/FixedWingPathFollower/fixedwingpathfollower.c @@ -63,6 +63,7 @@ #include "taskinfo.h" #include +#include "sin_lookup.h" #include "paths.h" #include "CoordinateConversions.h" @@ -85,6 +86,7 @@ static void updatePathVelocity(); static uint8_t updateFixedDesiredAttitude(); static void updateFixedAttitude(); static void airspeedStateUpdatedCb(UAVObjEvent *ev); +static bool correctCourse(float *C, float *V, float *F, float s); /** * Initialise the module, called on startup @@ -316,14 +318,16 @@ static void updatePathVelocity() // scale to correct length float l = sqrtf(velocityDesired.North * velocityDesired.North + velocityDesired.East * velocityDesired.East); - velocityDesired.North *= groundspeed / l; - velocityDesired.East *= groundspeed / l; + if (l > 0.0f) { + velocityDesired.North *= groundspeed / l; + velocityDesired.East *= groundspeed / l; + } float downError = altitudeSetpoint - positionState.Down; - velocityDesired.Down = downError * fixedwingpathfollowerSettings.VerticalPosP; + velocityDesired.Down = downError * fixedwingpathfollowerSettings.VerticalPosP; // update pathstatus - pathStatus.error = progress.error; + pathStatus.error = progress.error; pathStatus.fractional_progress = progress.fractional_progress; VelocityDesiredSet(&velocityDesired); @@ -372,8 +376,7 @@ static uint8_t updateFixedDesiredAttitude() AirspeedStateData airspeedState; SystemSettingsData systemSettings; - float groundspeedState; - float groundspeedDesired; + float groundspeedProjection; float indicatedAirspeedState; float indicatedAirspeedDesired; float airspeedError; @@ -384,13 +387,9 @@ static uint8_t updateFixedDesiredAttitude() float descentspeedError; float powerCommand; + float airspeedVector[2]; float fluidMovement[2]; - float heading; - float headingError; - float correctedHeading; - float course; float courseComponent[2]; - float correctedCourse; float courseError; float courseCommand; @@ -405,60 +404,47 @@ static uint8_t updateFixedDesiredAttitude() SystemSettingsGet(&systemSettings); /** - * Calculate where we are heading and why (wind issues) + * Compute speed error and course */ - heading = RAD2DEG(atan2f(velocityState.East, velocityState.North)); - headingError = heading - attitudeState.Yaw; - if (headingError < -180.0f) { - headingError += 360.0f; - } - if (headingError > 180.0f) { - headingError -= 360.0f; - } - // Error condition: wind speed is higher than airspeed. We are forced backwards! + + // 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 + airspeedVector[0] = cos_lookup_deg(attitudeState.Yaw); + airspeedVector[1] = sin_lookup_deg(attitudeState.Yaw); + + // 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, + // but thanks to accelerometers, groundspeedProjection reacts faster to changes in direction + // 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]); + + courseComponent[0] = velocityDesired.North - fluidMovement[0]; + courseComponent[1] = velocityDesired.East - fluidMovement[1]; + + indicatedAirspeedDesired = boundf(sqrtf(courseComponent[0] * courseComponent[0] + courseComponent[1] * courseComponent[1]), + 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 + + 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 ((headingError > fixedwingpathfollowerSettings.Safetymargins.Wind || - headingError < -fixedwingpathfollowerSettings.Safetymargins.Wind) && + if ((!valid) && fixedwingpathfollowerSettings.Safetymargins.Wind > 0.5f) { // alarm switched on - // we are flying backwards fixedwingpathfollowerStatus.Errors.Wind = 1; result = 0; } - - /** - * Compute speed error (required for thrust and pitch) - */ - - // Current ground speed - groundspeedState = sqrtf(velocityState.East * velocityState.East + velocityState.North * velocityState.North); - // assume groundspeed is negative if we are flying backwards (otherwise increasing airspeed would reduce groundspeed) - if (fabsf(headingError) > 90.0f) { - groundspeedState = -groundspeedState; - } - - // note that airspeedStateBias is ( calibratedAirspeed - groundSpeed ) at the time of measurement, - // but thanks to accelerometers, groundspeed reacts faster to changes in direction - // than airspeed and gps sensors alone - indicatedAirspeedState = groundspeedState + indicatedAirspeedStateBias; - - // fluidMovement is a vector describing the aproximate movement vector in surrounding fluid (2d) - fluidMovement[0] = indicatedAirspeedState * cosf(DEG2RAD(attitudeState.Yaw)); - fluidMovement[1] = indicatedAirspeedState * sinf(DEG2RAD(attitudeState.Yaw)); - - // Desired ground speed - groundspeedDesired = sqrtf(velocityDesired.North * velocityDesired.North + velocityDesired.East * velocityDesired.East); - // take negative speeds into account (if we are supposed to go the opposite way) - // this has two advantages: - // 1. it reduces speed to minimum for tight turns -- reducing speed = turn quicker - especially since we pull up to reduce speed ;) - // 2. in the unlikely case that we can fly backwards in strong headwind, we will - leads to awesome position hold ;) - if ((velocityDesired.North * fluidMovement[0] + velocityDesired.East * fluidMovement[1]) < 0.0f) { // difference >90 degrees - groundspeedDesired = -groundspeedDesired; - } - indicatedAirspeedDesired = boundf(groundspeedDesired + indicatedAirspeedStateBias, - fixedwingpathfollowerSettings.HorizontalVelMin, - fixedwingpathfollowerSettings.HorizontalVelMax); - // Airspeed error airspeedError = indicatedAirspeedDesired - indicatedAirspeedState; @@ -489,16 +475,10 @@ static uint8_t updateFixedDesiredAttitude() result = 0; } - if (indicatedAirspeedState < 1e-6f) { - // prevent division by zero, abort without controlling anything. This guidance mode is not suited for takeoff or touchdown, or handling stationary planes - // also we cannot handle planes flying backwards, lets just wait until the nose drops - fixedwingpathfollowerStatus.Errors.Lowspeed = 1; - return 0; - } - /** * 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, @@ -595,26 +575,25 @@ static uint8_t updateFixedDesiredAttitude() /** * Compute desired roll command */ - - // Calculate wind corrected heading angle - this approach avoids oscillation at high airspeed but low groundspeed situations (headwind) - correctedHeading = RAD2DEG(atan2f(velocityState.East + fluidMovement[1], velocityState.North + fluidMovement[0])); - - course = RAD2DEG(atan2f(velocityDesired.East, velocityDesired.North)); - if (groundspeedDesired >= 0.0f || groundspeedDesired <= fixedwingpathfollowerSettings.HorizontalVelMin - indicatedAirspeedStateBias) { - courseComponent[0] = 2.0f *indicatedAirspeedState *cosf(DEG2RAD(course)); - courseComponent[1] = 2.0f *indicatedAirspeedState *sinf(DEG2RAD(course)); - } else { // small negative groundspeeds can be achieved if flying slowly into head wind - this allows hovering on the spot ;) - courseComponent[0] = -groundspeedDesired *cosf(DEG2RAD(course)); - courseComponent[1] = -groundspeedDesired *sinf(DEG2RAD(course)); - } - correctedCourse = RAD2DEG(atan2f(courseComponent[1] + fluidMovement[1], courseComponent[0] + fluidMovement[0])); - - courseError = correctedCourse - correctedHeading; + courseError = RAD2DEG(atan2f(courseComponent[1], courseComponent[0])) - attitudeState.Yaw; if (courseError < -180.0f) { - courseError += 360.0f; + courseError += 360; } if (courseError > 180.0f) { + courseError -= 360; + } + + // overlap calculation. Theres a dead zone behind the craft where the + // counter-yawing of some craft while rolling could render a desired right + // turn into a desired left turn. Making the turn direction based on + // current roll angle keeps the plane committed to a direction once chosen + if (courseError < -180.0f + (fixedwingpathfollowerSettings.ReverseCourseOverlap * 0.5f) + && attitudeState.Roll > 0.0f) { + courseError += 360.0f; + } + if (courseError > 180.0f - (fixedwingpathfollowerSettings.ReverseCourseOverlap * 0.5f) + && attitudeState.Roll < 0.0f) { courseError -= 360.0f; } @@ -668,10 +647,100 @@ static void airspeedStateUpdatedCb(__attribute__((unused)) UAVObjEvent *ev) AirspeedStateGet(&airspeedState); VelocityStateGet(&velocityState); - float groundspeed = sqrtf(velocityState.East * velocityState.East + velocityState.North * velocityState.North); + float airspeedVector[2]; + float yaw; + AttitudeStateYawGet(&yaw); + airspeedVector[0] = cos_lookup_deg(yaw); + airspeedVector[1] = sin_lookup_deg(yaw); + // vector projection of groundspeed on airspeed vector to handle both forward and backwards movement + float groundspeedProjection = velocityState.North * airspeedVector[0] + velocityState.East * airspeedVector[1]; - - indicatedAirspeedStateBias = airspeedState.CalibratedAirspeed - groundspeed; - // note - we do fly by Indicated Airspeed (== calibrated airspeed) - // however since airspeed is updated less often than groundspeed, we use sudden changes to groundspeed to offset the airspeed by the same measurement. + // 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 + // changes to groundspeed to offset the airspeed by the same measurement. + // This has a side effect that in the absence of any airspeed updates, the + // pathfollower will fly using groundspeed. +} + + +/** + * Function to correct course C based on airspeed s, fluid movement F and desired movement vector V + */ +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 + // but at least making progress orthogonal to wind) + + s = fabsf(s); + float f = sqrtf(F[0] * F[0] + F[1] * F[1]); + + // normalize V + 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) + C[0] = -F[0]; + C[1] = -F[1]; + return fabsf(f - s) < 1e-3f; // returns true if a hover is actually intended + } + 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) + 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) + 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 + C[0] = V[0]; + C[1] = V[1]; + return false; + } else if (k2 <= 1e-3f) { + // there is 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 + // 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 + 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)) { + C[0] = C1[0]; + C[1] = C1[1]; + return true; + } + C[0] = C2[0]; + C[1] = C2[1]; + if (vp2 >= 0.0f) { + return true; + } else { + return false; + } } diff --git a/shared/uavobjectdefinition/fixedwingpathfollowersettings.xml b/shared/uavobjectdefinition/fixedwingpathfollowersettings.xml index 9be020de8..83bc91e25 100644 --- a/shared/uavobjectdefinition/fixedwingpathfollowersettings.xml +++ b/shared/uavobjectdefinition/fixedwingpathfollowersettings.xml @@ -12,6 +12,8 @@ + +