Cleanup and add comments

diff --git a/src/modules/robot/Robot.cpp b/src/modules/robot/Robot.cpp
index a98c1a4..d63b4e5 100644 (file)
--- a/src/modules/robot/Robot.cpp
+++ b/src/modules/robot/Robot.cpp
@@ -1460,31 +1460,31 @@ bool Robot::append_arc(Gcode * gcode, const float target[], const float offset[]
     float center_axis0 = this->arc_milestone[this->plane_axis_0] + offset[this->plane_axis_0];
     float center_axis1 = this->arc_milestone[this->plane_axis_1] + offset[this->plane_axis_1];
     float linear_travel = target[this->plane_axis_2] - this->arc_milestone[this->plane_axis_2];
-    float r_axis0 = -offset[this->plane_axis_0]; // Radius vector from center to current location
+    float r_axis0 = -offset[this->plane_axis_0]; // Radius vector from center to start position
     float r_axis1 = -offset[this->plane_axis_1];
-    float rt_axis0 = target[this->plane_axis_0] - this->arc_milestone[this->plane_axis_0] - offset[this->plane_axis_0];
+    float rt_axis0 = target[this->plane_axis_0] - this->arc_milestone[this->plane_axis_0] - offset[this->plane_axis_0]; // Radius vector from center to target position
     float rt_axis1 = target[this->plane_axis_1] - this->arc_milestone[this->plane_axis_1] - offset[this->plane_axis_1];
     float angular_travel = 0;
-
+    //check for condition where atan2 formula will fail due to everything canceling out exactly
     if((this->arc_milestone[this->plane_axis_0]==target[this->plane_axis_0]) && (this->arc_milestone[this->plane_axis_1]==target[this->plane_axis_1])) {
-        if (is_clockwise) {
+        if (is_clockwise) { // set angular_travel to -2pi for a clockwise full circle
            angular_travel = (-2 * PI);
-        } else {
+        } else { // set angular_travel to 2pi for a counterclockwise full circle
            angular_travel = (2 * PI);
         }
     } else {
         // Patch from GRBL Firmware - Christoph Baumann 04072015
         // CCW angle between position and target from circle center. Only one atan2() trig computation required.
-        // Only run if not a full circle
+        // Only run if not a full circle or angular travel will incorrectly result in 0.0f
         angular_travel = atan2f(r_axis0 * rt_axis1 - r_axis1 * rt_axis0, r_axis0 * rt_axis0 + r_axis1 * rt_axis1);
         if (plane_axis_2 == Y_AXIS) { is_clockwise = !is_clockwise; }  //Math for XZ plane is reverse of other 2 planes
-        if (is_clockwise) { // Correct atan2 output per direction
+        if (is_clockwise) { // adjust angular_travel to be in the range of -2pi to 0 for clockwise arcs
            if (angular_travel > 0) { angular_travel -= (2 * PI); }
-        } else {
+        } else {  // adjust angular_travel to be in the range of 0 to 2pi for counterclockwise arcs
            if (angular_travel < 0) { angular_travel += (2 * PI); }
         }
     }
-    
+
     // Find the distance for this gcode
     float millimeters_of_travel = hypotf(angular_travel * radius, fabsf(linear_travel));