Hi,
here is a small patch for YASim, which introduces initial loads to the
springs. With it you can tame e. g. the jitter of the beaver.
It is a local diff to my last gear-patch. In principle it is independent
from the last patch, but it is within the same lines of code, so the
patch tool probably will fail if you patch the cvs-files.
Please find enclosed a cvs-diff for the documentation as well as a
cvs-diff for the beaver (including the last patch).
@Andy: please commit to cvs.
Maik
Index: dhc2F.xml
===================================================================
RCS file: /var/cvs/FlightGear-0.9/data/Aircraft/dhc2/dhc2F.xml,v
retrieving revision 1.7
diff -u -p -r1.7 dhc2F.xml
--- dhc2F.xml 5 Sep 2006 19:03:42 -0000 1.7
+++ dhc2F.xml 1 Jan 2007 20:53:47 -0000
@@ -68,58 +68,110 @@
<!-- Floats-->
- <gear x="3.28" y="1.5" z="-2.06" compression="0.2" spring = "2" sfric =
"2.5">
- <control-input control="BRAKE" axis="/controls/gear/brake-parking" />
- <control-input control="BRAKE" axis="/controls/gear/brake-left" />
+ <gear x="3.52" y="1.5" z="-2.4" compression="0.7" spring = "10" sfric =
"0.8" dfric = "0.6" ignored-by-solver="1"
+ on-water="1" on-solid="0" reduce-friction-by-extension="1.25"
+ speed-planing="15" spring-factor-not-planing="0.15">
</gear>
- <gear x="3.28" y="-1.5" z="-2.06" compression="0.2" spring = "2" sfric =
"2.5">
- <control-input control="BRAKE" axis="/controls/gear/brake-parking" />
- <control-input control="BRAKE" axis="/controls/gear/brake-right" />
+ <gear x="3.52" y="-1.5" z="-2.4" compression="0.7" spring = "10" sfric =
"0.8" dfric = "0.6" ignored-by-solver="1"
+ on-water="1" on-solid="0" reduce-friction-by-extension="1.25"
+ speed-planing="15" spring-factor-not-planing="0.15">
</gear>
- <gear x="-3.25" y="1.5" z="-1.6" compression="0.2" spring = "2" sfric =
"2.5">
- <control-input axis="/controls/flight/rudder" control="STEER"
-invert="true" square="true"/>
+ <gear x="0.0" y="1.5" z="-2.1" compression="0.7" spring = "10" sfric = "0.8"
dfric = "0.6" ignored-by-solver="1"
+ on-water="1" on-solid="0" reduce-friction-by-extension="1.25"
+ speed-planing="25" spring-factor-not-planing="0.15">
</gear>
- <gear x="-3.25" y="-1.5" z="-1.6" compression="0.2" spring = "2" sfric =
"2.5">
- <control-input axis="/controls/flight/rudder" control="STEER"
-invert="true" square="true"/>
+ <gear x="0.0" y="-1.5" z="-2.1" compression="0.7" spring = "10" sfric =
"0.8" dfric = "0.6" ignored-by-solver="1"
+ on-water="1" on-solid="0" reduce-friction-by-extension="1.25"
+ speed-planing="25" spring-factor-not-planing="0.15">
</gear>
-
- <!-- Retractable wheels-->
- <gear x="3.52" y="1.5" z="-2.57" compression="0.2" spring = "3" sfric =
"2.5" retract-time="4">
+
+ <!-- Retractable wheels-->
+
+ <gear x="3.52" y="1.5" z="-2.57" compression="0.2" spring = "2" sfric =
"0.5" dfric=".45" retract-time="4" initial-load="0" damp="0.6">
<control-input control="STEER" axis="/controls/flight/rudder"
square="true"/>
<control-input axis="/controls/gear/gear-down" control="EXTEND"/>
<control-output control="EXTEND" prop="/gear/gear[4]/position-norm"/>
<control-speed control="EXTEND" transition-time="4"/>
</gear>
- <gear x="3.52" y="-1.5" z="-2.57" compression="0.2" spring = "3" sfric =
"2.5" retract-time="4">
+ <gear x="3.52" y="-1.5" z="-2.57" compression="0.2" spring = "2" sfric =
"0.5" dfric=".45" retract-time="4" initial-load="0" damp="0.6">
<control-input control="STEER" axis="/controls/flight/rudder"
square="true"/>
<control-input axis="/controls/gear/gear-down" control="EXTEND"/>
<control-output control="EXTEND" prop="/gear/gear[5]/position-norm"/>
<control-speed control="EXTEND" transition-time="4"/>
</gear>
- <gear x="-0.22" y="1.5" z="-2.57" compression="0.2" spring = "3" sfric =
"2.5" retract-time="4">
- <control-input control="BRAKE" axis="/controls/gear/brake-parking" />
- <control-input control="BRAKE" axis="/controls/gear/brake-left" />
- <control-input axis="/controls/gear/gear-down" control="EXTEND"/>
- <control-output control="EXTEND" prop="/gear/gear[6]/position-norm"/>
- <control-speed control="EXTEND" transition-time="4"/>
+ <gear x="-0.22" y="1.5" z="-2.57" compression="0.2" spring = "3.5" sfric =
"0.5" dfric=".45" retract-time="4" initial-load="1" damp="10.1">
+ <control-input control="BRAKE" axis="/controls/gear/brake-parking" />
+ <control-input control="BRAKE" axis="/controls/gear/brake-left" />
+ <control-input axis="/controls/gear/gear-down" control="EXTEND"/>
+ <control-output control="EXTEND" prop="/gear/gear[6]/position-norm"/>
+ <control-speed control="EXTEND" transition-time="4"/>
</gear>
-
- <gear x="-0.22" y="-1.5" z="-2.57" compression="0.2" spring = "3" sfric =
"2.5" retract-time="4">
+
+ <gear x="-0.22" y="-1.5" z="-2.57" compression="0.2" spring = "3.5" sfric =
"0.5" dfric=".45" retract-time="4" initial-load="1" damp="10.1">
<control-input control="BRAKE" axis="/controls/gear/brake-parking" />
<control-input control="BRAKE" axis="/controls/gear/brake-right" />
<control-input axis="/controls/gear/gear-down" control="EXTEND"/>
<control-output control="EXTEND" prop="/gear/gear[7]/position-norm"/>
<control-speed control="EXTEND" transition-time="4"/>
</gear>
-
-<!-- Fuel --> <tank x="1.5" y="0" z="-0.7" capacity="210" />
+
+
+<!-- 2 more Floats, need to be at this position in the file to do not brake
the animation
+ "reduce-friction-by-extension" is reduced to get steering control-->
+
+ <gear x="-3.22" y="1.5" z="-2.0" compression="0.7" spring = "10" sfric =
"0.8" dfric = "0.6" ignored-by-solver="1"
+ on-water="1" on-solid="0"
reduce-friction-by-extension="0.9"
+ speed-planing="25" spring-factor-not-planing="0.15">
+ <control-input axis="/controls/flight/rudder" control="STEER"
+ invert ="true" square="true"/>
+ </gear>
+ <gear x="-3.22" y="-1.5" z="-2.0" compression="0.7" spring = "10" sfric =
"0.8" dfric = "0.6" ignored-by-solver="1"
+ on-water="1" on-solid="0"
reduce-friction-by-extension="0.9"
+ speed-planing="25" spring-factor-not-planing="0.15">
+ <control-input axis="/controls/flight/rudder" control="STEER"
+ invert="true" square="true"/>
+ </gear>
+
+
+ <!-- The Floats on solid ground-->
+
+ <gear x="3.52" y="1.5" z="-2.4" compression="0.4" spring = "10" sfric =
"1.5" dfric = "1.3" skid="1" ignored-by-solver="1">
+ </gear>
+
+ <gear x="3.52" y="-1.5" z="-2.4" compression="0.4" spring = "10" sfric
= "1.5" dfric = "1.3" skid="1" ignored-by-solver="1">
+ </gear>
+
+ <gear x="0.0" y="1.5" z="-2.1" compression="0.2" spring = "10" sfric =
"1.5" dfric = "1.3" skid="1" ignored-by-solver="1">
+ </gear>
+
+ <gear x="0.0" y="-1.5" z="-2.1" compression="0.2" spring = "10" sfric =
"1.5" dfric = "1.3" skid="1" ignored-by-solver="1">
+ </gear>
+
+ <gear x="-3.22" y="1.5" z="-2.0" compression="0.2" spring = "10" sfric
= "1.5" dfric = "1.3" skid="1" ignored-by-solver="1">
+ </gear>
+
+ <gear x="-3.22" y="-1.5" z="-2.0" compression="0.2" spring = "10" sfric
= "1.5" dfric = "1.3" skid="1" ignored-by-solver="1">
+ </gear>
+
+
+ <!-- Retractable wheels on water-->
+ <gear x="-0.22" y="1.5" z="-2.57" compression="0.2" spring = "0.1"
sfric = "1" dfric="1" retract-time="4" on-water="1" on-solid="0"
ignored-by-solver="1" reduce-friction-by-extension="0.9">
+ <control-input axis="/controls/gear/gear-down"
control="EXTEND"/>
+ <control-speed control="EXTEND" transition-time="4"/>
+ </gear>
+
+ <gear x="-0.22" y="-1.5" z="-2.57" compression="0.2" spring = "0.1"
sfric = "1" dfric ="1" retract-time="4" on-water="1" on-solid="0"
ignored-by-solver="1" reduce-friction-by-extension="0.9">
+ <control-input axis="/controls/gear/gear-down"
control="EXTEND"/>
+ <control-speed control="EXTEND" transition-time="4"/>
+ </gear>
+
+
+ <!-- Fuel --> <tank x="1.5" y="0" z="-0.7" capacity="210" />
<tank x="0.0" y="0" z="-0.7" capacity="210" />
<tank x="-1.5" y="0" z="-0.7" capacity="156" />
Index: README.yasim
===================================================================
RCS file: /var/cvs/FlightGear-0.9/data/Docs/README.yasim,v
retrieving revision 1.17
diff -u -p -r1.17 README.yasim
--- README.yasim 10 Nov 2006 18:06:24 -0000 1.17
+++ README.yasim 1 Jan 2007 20:55:53 -0000
@@ -44,6 +44,15 @@ fuselage: This defines a tubelike struct
expressed as a fraction (0-1) of the width value.
midpoint: The location of the widest part of the fuselage,
expressed as a fraction of the distance between A and B.
+ idrag: Multiplier for the "induced drag" generated by this
+ object. Default is one. With idrag=0 the fuselage
+ generates only drag.
+ cx,cy,cz: Factors for the generated drag in the fuselages "local
+ coordinate system" with x pointing from end to front,
+ z perpendicular to x with y=0 in the aircraft coordinate
+ system. E.g. for a fuselage of a height of 2 times the
+ width you can define cy=2 and (due to the doubled front
+ surface) cx=2.
wing: This defines the main wing of the aircraft. You can have
only one (but see below about using vstab objects for extra
@@ -288,10 +297,22 @@ actionpt: Defines an "action point" for
x,y,z: The location of force application.
gear: Defines a landing gear. Accepts <control> subelements to map
- properties to steering and braking.
+ properties to steering and braking. Can also be used to simulate
+ floats. Although the coefficients are still called ..fric, it
+ is calculated in fluids as a drag (proportional to the square
+ of the speed). In fluids gears are not considured to detect
+ crashes (as on ground).
x,y,z: The location of the fully-extended gear tip.
compression: The distance in meters along the "up" axis that
the gear will compress.
+ initial-load: The initial load of the spring in multiples of
+ compression. Defaults to 0. (With this parameter
+ a lower spring-constants will be used for the
+ gear-> can reuce numerical problems (jitter))
+ Note: the spring-constant is varied from 0%
+ compression to 20% compression to get continous
+ behavior around 0 compression. (could be physically
+ explained by wheel deformation)
upx/upy/upz: The direction of compression, defaults to
vertical (0,0,1) if unspecified. These are
used only for a direction -- the vector need
@@ -312,6 +333,35 @@ gear: Defines a landing gear. Accep
unstable. If you can't make the gear stop
bouncing with this number, try increasing the
compression length instead.
+ on-water: if this is set to "0" the gear will be ignored if
+ on water. Defaults to "0"
+ on-solid: if this set to "0" the gear will be ignored if
+ not on water. Defaults to "1"
+ inverse-speed-spring-is-doubled: At this speed (the inverse of
+ the speed must be given) the spring constant
+ is doubled. The idea is, to use this on water to
+ simulate the speed dependend lift of a float.
+ Defaults to "0"
+ speed-planing:
+ spring-factor-not-planing:
+ At zero speed the spring factor is multiplied by
+ spring-factor-not-planing. Above speed_planing this
+ factor is equalt to 1. THe diea is, to use this for
+ floats simulating the transition from swimming to
+ planing. speed_planing defaults to 0,
+ spring-factor-not-planing defaults to 1.
+ reduce-friction-by-extension: at full extension the friction is
+ reduced by this relative value. 0.7 means 30% friction
+ at full extension. If you specify a value greater
+ than one, the friction will be zero before reaching
+ full extension. Defaults to "0"
+ ignored-by-solver: with the on-water/on-solid tags you can have more
+ than one set of gears in one aircraft, If the solver
+ (who automatically generates the spring constants)
+ would take all gears into account, the result would be
+ wrong. E. G. set this tag to "1" for all gears, which
+ are not active on runways. Defaults to "0". You can
+ not exclude all gears in the solving process.
launchbar: Defines a catapult launchbar or strop.
x,y,z: The location of the mount point of the launch bar or
@@ -469,6 +519,9 @@ rotor: A rotor. Used for simulating h
If you specify a rotor, you do not need to specify a wing or hstab,
the settings for approach and cruise will be ignored then. You have
to specify the solver results manually. See below.
+ The rotor generates downwash acting on all stabs, surfaces and
+ fuselages. For all fuselages in the rotor downwash you should
+ specify idrag="0" to get realistic results.
name: The name of the rotor.
(some data is stored at /rotors/name/)
@@ -481,7 +534,6 @@ rotor: A rotor. Used for simulating h
A value stall gives the fraction of the rotor in stall
(weighted by the fraction the have on lift and drag
without stall). Use this for modifying the rotor-sound.
- The torque property has a bug.
x,y,z: The position of the rotor center
nx,ny,nz: The normal of the rotor (pointing upwards, will be
normalized by the computer)
@@ -555,11 +607,6 @@ rotor: A rotor. Used for simulating h
is stall. In the range between this incidences it is
interpolated linear.
- The airfoil of the rotor can be described in two ways. First you
- can define the needed power for different pitch values and the
- total lift force at a user-defined pitch value. Don't use pitch
- values greater than the stall incidence. You could get strange
- results.
pitch-a:
pitch-b: collective incidence angles, If you start flightgear
@@ -573,6 +620,7 @@ rotor: A rotor. Used for simulating h
coefficients instead (see below) and adjust the lift with
rotor-correction-factor.
+ The airfoil of the rotor is described as follows:
The way is to define the lift and drag coefficients directly.
Without stall the c-lift of the profile is assumed to be
sin(incidence-"airfoil-incidence-no-lift")*liftcoef;
@@ -626,6 +674,8 @@ rotor: A rotor. Used for simulating h
So delta3 is the proportional factor between flapping and
decrease of incidence. I.e. the tail rotor of a Bo105 has
a delta3 of 1.
+ In some publications delta3 is described by an angle. The
+ value in YASim is the atan of this angle
delta: A factor for the damping constant for the flapping. 1 means
a analytical result, which is only a approximation. Has a
very strong result in the reaction of the rotor system on
@@ -688,7 +738,11 @@ rotorgear: If you are using one ore more
yasimliftfactor: the solver is not working with rotor-aircrafts.
Therefore you have to specify the results yourself.
10 for drag and 140 for lift seem to be good starting
- values.
+ values. Although the solve is not invoked for aircrafts
+ with at least one rotor, you need to specifiy the cruise
+ and the approach seetings. The approach speed is needed to
+ calculate the gear springs. Use a speed of approx. 50knots.
+ They do not need to match any real value.
The rotorgear needs a <control> subelement for the engine
(ROTORGEARENGINEON) and can have a <control> subelement for the
diff -up ./Airplane.cpp ../Airplane.cpp
--- ./Airplane.cpp 2006-12-24 00:56:39.873990400 +0100
+++ ../Airplane.cpp 2007-01-01 18:27:13.758169600 +0100
@@ -730,7 +730,7 @@ void Airplane::solveGear()
float e = energy * gr->wgt;
float comp[3];
gr->gear->getCompression(comp);
- float len = Math::mag3(comp);
+ float len = Math::mag3(comp)*(1+2*gr->gear->getInitialLoad());
// Energy in a spring: e = 0.5 * k * len^2
float k = 2 * e / (len*len);
Only in ..: CVS
diff -up ./FGFDM.cpp ../FGFDM.cpp
--- ./FGFDM.cpp 2006-12-31 13:25:43.804753600 +0100
+++ ../FGFDM.cpp 2007-01-01 17:07:00.397899200 +0100
@@ -269,6 +269,7 @@ void FGFDM::startElement(const char* nam
v[i] *= attrf(a, "compression", 1);
g->setCompression(v);
g->setBrake(attrf(a, "skid", 0));
+ g->setInitialLoad(attrf(a, "initial-load", 0));
g->setStaticFriction(attrf(a, "sfric", 0.8));
g->setDynamicFriction(attrf(a, "dfric", 0.7));
g->setSpring(attrf(a, "spring", 1));
diff -up ./Gear.cpp ../Gear.cpp
--- ./Gear.cpp 2006-12-31 14:37:14.003756800 +0100
+++ ../Gear.cpp 2007-01-01 20:53:43.137112000 +0100
@@ -21,6 +21,7 @@ Gear::Gear()
_dfric = 0.7f;
_brake = 0;
_rot = 0;
+ _initialLoad=0;
_extension = 1;
_castering = false;
_frac = 0;
@@ -140,6 +141,11 @@ void Gear::setReduceFrictionByExtension(
_reduceFrictionByExtension=s;
}
+void Gear::setInitialLoad(float l)
+{
+ _initialLoad=l;
+}
+
void Gear::setGlobalGround(double *global_ground, float* global_vel,
double globalX, double globalY,
int type, const SGMaterial *material)
@@ -368,7 +374,16 @@ void Gear::calcForce(RigidBody* body, St
// Finally, we can start adding up the forces. First the spring
// compression. (note the clamping of _frac to 1):
_frac = (_frac > 1) ? 1 : _frac;
- float fmag = _frac*clen*_spring;
+
+ // Add the initial load to frac, but with continous transistion around 0
+ float frac_with_initial_load;
+ if (_frac>0.2 || _initialLoad==0.0)
+ frac_with_initial_load=_frac+_initialLoad;
+ else
+ frac_with_initial_load=(_frac+_initialLoad)
+ *_frac*_frac*3*25-_frac*_frac*_frac*2*125;
+
+ float fmag = frac_with_initial_load*clen*_spring;
float inversespeed_multiplied_by_speed=0;
if (_inverseSpeedSpringIsDoubled>0.0000001) {
inversespeed_multiplied_by_speed=Math::mag3(cv)*_inverseSpeedSpringIsDoubled;
diff -up ./Gear.hpp ../Gear.hpp
--- ./Gear.hpp 2006-12-31 14:35:36.333313600 +0100
+++ ../Gear.hpp 2007-01-01 17:22:58.405446400 +0100
@@ -47,6 +47,7 @@ public:
void setSpringFactorNotPlaning(float f);
void setSpeedPlaning(float s);
void setReduceFrictionByExtension(float s);
+ void setInitialLoad(float l);
void setIgnoreWhileSolving(bool c);
void setGlobalGround(double* global_ground, float* global_vel,
double globalX, double globalY,
@@ -63,6 +64,7 @@ public:
float getBrake();
float getRotation();
float getExtension();
+ float getInitialLoad() {return _initialLoad; }
bool getCastering();
float getCasterAngle() { return _casterAngle; }
float getRollSpeed() { return _rollSpeed; }
@@ -103,6 +105,7 @@ private:
float _contact[3];
float _wow;
float _frac;
+ float _initialLoad;
float _compressDist;
double _global_ground[4];
float _global_vel[3];
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