added delta tower babystepping. Its untested, but hopefully florian horsch will be able to try.

also, removed some trouble for compilation with corexy.
I think that babystepping is only possible in z for a delta tower.
not sure if it would be usefull to step individual motors on a delta, i don't own one

Marlin/Configuration_adv.h

 // Babystepping enables the user to control the axis in tiny amounts, independently from the normal printing process
 // it can e.g. be used to change z-positions in the print startup phase in realtime
 // does not respect endstops!
-
 //#define BABYSTEPPING
-//#define BABYSTEP_XY  //not only z, but also XY
-
-#ifdef COREXY
+#ifdef BABYSTEPPING
+  #define BABYSTEP_XY  //not only z, but also XY in the menu. more clutter, more functions
+  #define BABYSTEP_INVERT_Z false  //true for inverse movements in Z
+  #define BABYSTEP_Z_MULTIPLICATOR 2 //faster z movements
+  
+  #ifdef COREXY
     #error BABYSTEPPING not implemented for COREXY yet.
+  #endif
+
+  #ifdef DELTA
+    #ifdef BABYSTEP_XY
+      #error BABYSTEPPING only implemented for Z axis on deltabots.
+    #endif
+  #endif
 #endif
 
 // extruder advance constant (s2/mm3)

Marlin/stepper.cpp

     #endif
 
   }
-  break; 
+  break;
+ 
+#ifndef DELTA
   case Z_AXIS:
   {
     enable_z();
     uint8_t old_z_dir_pin= READ(Z_DIR_PIN);  //if dualzstepper, both point to same direction.
     //setup new step
-    WRITE(Z_DIR_PIN,(INVERT_Z_DIR)^direction);
+    WRITE(Z_DIR_PIN,(INVERT_Z_DIR)^direction^BABYSTEP_INVERT_Z);
     #ifdef Z_DUAL_STEPPER_DRIVERS
-      WRITE(Z2_DIR_PIN,(INVERT_Z_DIR)^direction);
+      WRITE(Z2_DIR_PIN,(INVERT_Z_DIR)^direction^BABYSTEP_INVERT_Z);
     #endif
     //perform step 
     WRITE(Z_STEP_PIN, !INVERT_Z_STEP_PIN); 
 
   }
   break;
+#else //DELTA
+  case Z_AXIS:
+  {
+    enable_x();
+    enable_y();
+    enable_z();
+    uint8_t old_x_dir_pin= READ(X_DIR_PIN);  
+    uint8_t old_y_dir_pin= READ(Y_DIR_PIN);  
+    uint8_t old_z_dir_pin= READ(Z_DIR_PIN);  
+    //setup new step
+    WRITE(X_DIR_PIN,(INVERT_X_DIR)^direction^BABYSTEP_INVERT_Z);
+    WRITE(Y_DIR_PIN,(INVERT_Y_DIR)^direction^BABYSTEP_INVERT_Z);
+    WRITE(Z_DIR_PIN,(INVERT_Z_DIR)^direction^BABYSTEP_INVERT_Z);
+    
+    //perform step 
+    WRITE(X_STEP_PIN, !INVERT_X_STEP_PIN); 
+    WRITE(Y_STEP_PIN, !INVERT_Y_STEP_PIN); 
+    WRITE(Z_STEP_PIN, !INVERT_Z_STEP_PIN); 
+    
+    //wait a tiny bit
+    {
+    float x=1./float(axis+1); //absolutely useless
+    }
+    WRITE(X_STEP_PIN, INVERT_X_STEP_PIN); 
+    WRITE(Y_STEP_PIN, INVERT_Y_STEP_PIN); 
+    WRITE(Z_STEP_PIN, INVERT_Z_STEP_PIN);
+
+    //get old pin state back.
+    WRITE(X_DIR_PIN,old_x_dir_pin);
+    WRITE(Y_DIR_PIN,old_y_dir_pin);
+    WRITE(Z_DIR_PIN,old_z_dir_pin);
+
+  }
+  break;
+#endif
  
   default:    break;
   }

Marlin/ultralcd.cpp

 {
     if (encoderPosition != 0)
     {
-        babystepsTodo[Z_AXIS]+=(int)encoderPosition;
+        babystepsTodo[Z_AXIS]+=BABYSTEP_Z_MULTIPLICATOR*(int)encoderPosition;
         encoderPosition=0;
         lcdDrawUpdate = 1;
     }