From 0b1c282921f7d7bf8e3c3567aee918ce640955d3 Mon Sep 17 00:00:00 2001
From: Fisch <interfisch@gmx.net>
Date: Sat, 12 May 2018 00:24:02 +0200
Subject: [PATCH] improve airresistance

---
 achterbahn.ino |  2 +-
 wagon.cpp      | 17 +++++++++++++----
 2 files changed, 14 insertions(+), 5 deletions(-)

diff --git a/achterbahn.ino b/achterbahn.ino
index a79f9d6..63f68e5 100644
--- a/achterbahn.ino
+++ b/achterbahn.ino
@@ -17,7 +17,7 @@ long lastRoutineUpdate=0;
 #define ROUTINEUPDATETIME 20
 long lastCheckspawn=0;
 #define CHECKSPAWNDELAY 4000 //delay in ms to check random spawn
-#define SPAWNCHANCE 30 //1 out of x times wagon will spawn
+#define SPAWNCHANCE 20 //1 out of x times wagon will spawn
 #define SPAWNCHANCEDOUBLE 5 //change of spawning a two trains simultaneously
 
 long loopmillis=0;
diff --git a/wagon.cpp b/wagon.cpp
index 9941fd5..56f0821 100644
--- a/wagon.cpp
+++ b/wagon.cpp
@@ -15,7 +15,7 @@ Wagon::Wagon(int id,int numpixels, Adafruit_NeoPixel *strip,uint8_t *height,floa
   _height=height;
   _vel=startvel;
   _acc=startacc;
-  _wagonmass=wagonmass;
+  _wagonmass=wagonmass; //mass of whole train
   _spawntime=millis();
   _lasttimefast=millis();
   _wagoncolor=wagoncolor;
@@ -46,7 +46,9 @@ void Wagon::updatePhysics(float updatedelayms)
   #define CONST_G 9.81
   #define PIXELDISTANCE 1.6666667 // 1/60.0 * 100 
   #define C_ROLL 0.001 // = Croll * G    https://de.wikipedia.org/wiki/Rollwiderstand   0.001
-  #define AIRRES 0.18 //C_w*A*0.5*rho     Air resistance:  C_w * A * 0.5 * rho  (.... *v^2)
+  #define AIRRESFIRST 0.18 //C_w*A*0.5*rho     Air resistance:  C_w * A * 0.5 * rho  (.... *v^2)
+  #define AIRRES 0.01 //for slipstream at second wagon
+  #define AIRRESMUL 0.7 //how much of air resistance the next wagon has
   //http://www.kfz-tech.de/Biblio/Formelsammlung/Luftwiderstand.htm   C_w 0.6 
   //rho  Massendichte luft  1,2041
   //A = 1m^2
@@ -55,6 +57,7 @@ void Wagon::updatePhysics(float updatedelayms)
 
   _acc=0;
   int cpos=(int)_pos;
+  uint8_t wagonnumber=0;
   for (int cpos=(int)_pos;cpos>(int)(_pos-_trainlength);cpos--){ //for each wagon
 
     float hdiff=getHeight((int) (cpos-0.5)) - getHeight((int)(cpos+0.5));
@@ -74,7 +77,13 @@ void Wagon::updatePhysics(float updatedelayms)
     if (_vel<0){
       bb*=-1;
     }
-    float cc=AIRRES/m*pow(_vel,2); //air resistance
+    float cc=0;
+    if (wagonnumber==0){ //first wagon
+      cc=AIRRESFIRST/m*pow(_vel,2); //air resistance for first wagon
+    }else{
+      cc=AIRRES/m*pow(_vel,2) *pow(AIRRESMUL,wagonnumber-1); //air resistance 
+      
+    }
     if (_vel<0){
       cc*=-1;
     }
@@ -86,7 +95,7 @@ void Wagon::updatePhysics(float updatedelayms)
 
     _acc += aa - bb - cc;
     
-
+    wagonnumber++;
   }
 
   _acc*=updatedelayms/1000;