diff --git a/api/src/main/java/ru/dragonestia/msb3/api/math/Quaternion.java b/api/src/main/java/ru/dragonestia/msb3/api/math/Quaternion.java
index bcce778..16df674 100644
--- a/api/src/main/java/ru/dragonestia/msb3/api/math/Quaternion.java
+++ b/api/src/main/java/ru/dragonestia/msb3/api/math/Quaternion.java
@@ -6,6 +6,10 @@ public record Quaternion(double x, double y, double z, double w) {
 
     public static final Quaternion DEFAULT = new Quaternion(0, 0, 0, 1);
 
+    public static Quaternion fromVec (Vec vec, double realPart) {
+        return new Quaternion(vec.x(), vec.y(), vec.z(), realPart);
+    }
+
     public float[] toFloatArray() {
         return new float[] { (float) x, (float) y, (float) z, (float) w };
     }
@@ -23,6 +27,11 @@ public record Quaternion(double x, double y, double z, double w) {
         return new Quaternion(-x, -y, -z, w);
     }
 
+    public double dotProduct(Quaternion target) {
+        return (x * target.x + y * target.y + z * target.z + w * target.w
+        );
+    }
+
     public Quaternion mul(Quaternion target) {
         return new Quaternion(
             w() * target.x() + x() * target.w() + y() * target.z() - z() * target.y(),
@@ -32,15 +41,34 @@ public record Quaternion(double x, double y, double z, double w) {
         );
     }
 
+    public Quaternion add(Quaternion target) {
+        return new Quaternion(
+                x + target.x,
+                y + target.y,
+                z + target.z,
+                w + target.w
+        );
+    }
+
+    public Quaternion sub(Quaternion target) {
+        return new Quaternion(
+                x - target.x,
+                y - target.y,
+                z - target.z,
+                w - target.w
+        );
+    }
+
     public Quaternion rotate(Vec normal) {
         var defaultQuaternion = new Quaternion(0, 0, 0, 1);
         var defaultVector = new Vec(0, 1, 0);
 
         var feta = Math.acos(defaultVector.dot(normal));
-        var r = defaultVector.cross(normal).normalize();
-        var r_sin = r.mul(Math.sin(feta/2));
-
-        var rotation = new Quaternion(r_sin.x(), r_sin.y(), r_sin.z(), Math.cos(feta/2));
+        var r = defaultVector.cross(normal);
+        if (r.isZero()){
+            r = new Vec(0, 0, 1);
+        }
+        var rotation = fromVec(r.normalize().mul(Math.sin(feta / 2)), Math.cos(feta / 2));
         return defaultQuaternion.mul(rotation);
     }
 }