Align bucket pivot and lugs with arm tip, update offsets

Added BUCKET_PIVOT_Y_OFFSET to shift the bucket and lugs for proper alignment with the arm tip pin hole. Updated kinematic and visual parameters in lifetrac_v25_params.scad and lifetrac_v25.scad to use this offset, ensuring the lug back is flush with the bucket back plate as specified in DESIGN_RULES.md. Added verification code for bucket position at ground contact and clarified parameter usage for visual vs. kinematic arm leg length.

Author: dorkmo

LifeTrac-v25/mechanical_design/DESIGN_RULES.md

@@ -16,6 +16,7 @@ This document establishes the non-negotiable geometric rules and parametric cons
 *   **Crash Prevention**: The solver must prioritize the Target Point, but validity checks must ensure the arm tip material (steel extending below the pivot) does not crash into the ground before the bucket does.
 
 ## 3. Physical Component Alignment
+*   **Lug Flush Mounting**: The back (base) of any U-channel lug or mounting bracket must be flush with the surface it is intended to be mounted to. For bucket pivot lugs, the lug back must be flush with the back plate of the bucket. No overlap or gap between lug base and mounting surface.
 *   **Matching Tip Radii**: The radius of the Loader Arm Tip (`boss_r` in `arm_plate.scad`) must visually and dimensionally match the Bucket Pivot Lugs to ensure a clean hinge assembly.
     *   Constraint: `boss_r` == `PIVOT_HOLE_X_FROM_FRONT`.
 *   **Hole Alignment**: The physical hole cut into the *Arm Plate* must strictly match the kinematic point `_T`.

LifeTrac-v25/mechanical_design/openscad/lifetrac_v25.scad

@@ -362,15 +362,16 @@ function bucket_cyl_length(arm_angle, bucket_tilt) =
         // Bucket attachment (in bucket local, tilt about arm tip, then arm rotation)
         // Must match the translation in bucket_attachment
         // Bucket is at Y = BUCKET_LUG_OFFSET. Cylinder Lug is on back plate.
-        // Assuming Cylinder Lug is also rotated to point backwards, Pivot is at Y=0 relative to Arm Tip?
-        // Let's assume Cylinder Lug Pivot is at Y = 0 for now (flush with Arm Pivot Y)
+        // BUCKET_PIVOT_Y_OFFSET shifts the entire bucket pivot assembly toward/away from arms
+        // Cylinder Lug Pivot is at Y=0 relative to the shifted bucket pivot
         bucket_local_y = 0,
         bucket_local_z = BUCKET_CYL_MOUNT_Z_OFFSET + (BUCKET_HEIGHT - BUCKET_PIVOT_HEIGHT_FROM_BOTTOM),
         // Tilt about bucket pivot (at arm tip)
         bucket_tilted_y = bucket_local_y * cos(bucket_tilt) - bucket_local_z * sin(bucket_tilt),
         bucket_tilted_z = bucket_local_y * sin(bucket_tilt) + bucket_local_z * cos(bucket_tilt),
         // Add arm length to get position relative to arm pivot
-        bucket_arm_y = ARM_TIP_X + bucket_tilted_y,
+        // Include BUCKET_PIVOT_Y_OFFSET to match bucket_attachment positioning
+        bucket_arm_y = ARM_TIP_X + BUCKET_PIVOT_Y_OFFSET + bucket_tilted_y,
         bucket_arm_z = ARM_TIP_Z + bucket_tilted_z,
         // Rotate by arm angle
         bucket_y = bucket_arm_y * cos(arm_angle) - bucket_arm_z * sin(arm_angle),
@@ -468,6 +469,24 @@ echo("Stroke with margin:", BUCKET_CYL_STROKE_WITH_MARGIN, "mm");
 echo("SELECTED BUCKET CYLINDER STROKE:", BUCKET_CYLINDER_STROKE, "mm");
 echo("Recommended closed length:", BUCKET_CYL_CLOSED_LENGTH, "mm");
 
+// =============================================================================
+// BUCKET POSITION VERIFICATION (at $t=0, arms at ground)
+// =============================================================================
+// Verify bucket bottom touches ground when arms are lowered and bucket is flat
+_bucket_pivot_z_target = BUCKET_PIVOT_HEIGHT_FROM_BOTTOM + BUCKET_GROUND_CLEARANCE; // 90mm
+_bucket_translation_z = BUCKET_HEIGHT - BUCKET_PIVOT_HEIGHT_FROM_BOTTOM + BUCKET_BODY_Z_OFFSET + BUCKET_VISUAL_Z_OFFSET;
+_bucket_bottom_offset_from_pivot = _bucket_translation_z - BUCKET_HEIGHT; // Should equal -BUCKET_PIVOT_HEIGHT_FROM_BOTTOM
+_bucket_bottom_world_z = _bucket_pivot_z_target + _bucket_bottom_offset_from_pivot; // Should be 0 for flat on ground
+
+echo("=== BUCKET POSITION VERIFICATION ===");
+echo("BUCKET_PIVOT_Z_TARGET (arm tip at ground) =", _bucket_pivot_z_target, "mm");
+echo("BUCKET_HEIGHT =", BUCKET_HEIGHT, "mm");
+echo("BUCKET_PIVOT_HEIGHT_FROM_BOTTOM =", BUCKET_PIVOT_HEIGHT_FROM_BOTTOM, "mm");
+echo("BUCKET_VISUAL_Z_OFFSET =", BUCKET_VISUAL_Z_OFFSET, "mm");
+echo("Bucket translation Z =", _bucket_translation_z, "mm");
+echo("Bucket bottom offset from pivot =", _bucket_bottom_offset_from_pivot, "mm");
+echo("BUCKET BOTTOM WORLD Z (should be 0) =", _bucket_bottom_world_z, "mm");
+
 // =============================================================================
 // LIFTING CAPACITY CALCULATIONS
 // =============================================================================
@@ -2301,9 +2320,10 @@ module bucket_attachment() {
     if (show_bucket) {
         translate([0, ARM_PIVOT_Y, ARM_PIVOT_Z])
         rotate([is_undef(ARM_LIFT_ANGLE) ? 0 : ARM_LIFT_ANGLE, 0, 0])
-        translate([0, ARM_TIP_X, ARM_TIP_Z])
+        translate([0, ARM_TIP_X + BUCKET_PIVOT_Y_OFFSET, ARM_TIP_Z])
         {
             // Bucket rotates about this pivot
+            // BUCKET_PIVOT_Y_OFFSET shifts bucket and lugs together toward/away from arms
             rotate([BUCKET_TILT_ANGLE, 0, 0]) {
                 // Pivot Lugs: U-Channel brackets bolted to bucket back plate
                 // The Pivot Lug Hole must be at (0,0,0) of this group (which is the Arm Tip/Pivot).
@@ -2415,9 +2435,9 @@ module bucket_cylinders() {
             // Tilt about X at arm tip
             bucket_tilted = rot_x(bucket_local, BUCKET_TILT_ANGLE);
 
-            // Position relative to arm tip
+            // Position relative to arm tip (including BUCKET_PIVOT_Y_OFFSET)
             bucket_at_arm_tip = [bucket_tilted[0],
-                                ARM_TIP_X + bucket_tilted[1],
+                                ARM_TIP_X + BUCKET_PIVOT_Y_OFFSET + bucket_tilted[1],
                                 ARM_TIP_Z + bucket_tilted[2]];
 
             // Rotate by arm angle

LifeTrac-v25/mechanical_design/openscad/lifetrac_v25_params.scad

@@ -86,6 +86,12 @@ BUCKET_FRONT_CLEARANCE = BUCKET_FRONT_CLEARANCE_BASE + BUCKET_FRONT_CLEARANCE_AD
 // We align the pivot to be at 1/5 of the bucket height (standard stability position)
 BUCKET_PIVOT_HEIGHT_FROM_BOTTOM = BUCKET_HEIGHT / 5; // 450 / 5 = 90mm
 
+// Bucket Pivot Y Offset: Shifts bucket and lugs together toward/away from arms
+// Negative values move toward arms (back), positive moves away (forward)
+// Used to center the lug pin with the arm tip pin hole
+// DEFINED EARLY so arm kinematics can account for it
+BUCKET_PIVOT_Y_OFFSET = -2.5 * 25.4; // -63.5mm (~2.5 inches toward arms)
+
 // =============================================================================
 // LOADER ARM DIMENSIONS
 // =============================================================================
@@ -326,29 +332,44 @@ ARM_MAIN_LEN = _L_main_kinematic - ARM_OVERLAP + _geom_correction;
 ARM_DROP_EXT = 80; 
 PIVOT_HOLE_X_FROM_FRONT = BUCKET_PIVOT_PIN_DIA; // Reverted to 1" (25.4mm) per request (Forward position)
 
-ARM_DROP_LEN = _L_drop_kinematic - ARM_DROP_EXT + PIVOT_HOLE_X_FROM_FRONT; 
+// Leg shortening adjustment - shortens visual leg WITHOUT changing arm rotation
+// This raises the pin hole higher above ground while keeping main arm angle fixed
+// Target: Pin hole center at 1/5 bucket height (90mm) from ground level
+// The arm hole is at PIVOT_HOLE_Z_FROM_BOTTOM (127mm) from tube bottom
+ARM_LEG_SHORTEN = 37 + 25.4 + 6.35 + 25.4 + 6.35; // 100.5mm - added 0.25 inch to previous value
+
+// Visual leg length (what gets rendered)
+ARM_DROP_LEN = _L_drop_kinematic - ARM_DROP_EXT + PIVOT_HOLE_X_FROM_FRONT - ARM_LEG_SHORTEN; 
+
+// Kinematic leg length (used for tip position calculation - keeps arm angle unchanged)
+_ARM_DROP_LEN_KINEMATIC = _L_drop_kinematic - ARM_DROP_EXT + PIVOT_HOLE_X_FROM_FRONT; // Original unshortened
 
 ARM_PIVOT_EXT = 40; 
 PIVOT_HOLE_EDGE_OFFSET = 1.5 * 25.4; 
-// PIVOT_HOLE_Z_FROM_BOTTOM set to Top Edge (Tangent to Top)
-// This aligns the pivot with the "Upper/Outer" edge of the arm profile.
-PIVOT_HOLE_Z_FROM_BOTTOM = TUBE_2X6_1_4[1] - PIVOT_HOLE_X_FROM_FRONT; 
+// PIVOT_HOLE_Z_FROM_BOTTOM: Original position at top edge of tube
+// This keeps the hole position on the arm profile unchanged
+PIVOT_HOLE_Z_FROM_BOTTOM = TUBE_2X6_1_4[1] - PIVOT_HOLE_X_FROM_FRONT; // 127mm - original position
 
 echo("DEBUG: Final Parameters:");
 echo("  ARM_SHAPE_ANGLE:", ARM_SHAPE_ANGLE);
 echo("  ARM_MAIN_LEN:", ARM_MAIN_LEN);
-echo("  ARM_DROP_LEN:", ARM_DROP_LEN);
+echo("  ARM_DROP_LEN (visual):", ARM_DROP_LEN);
+echo("  _ARM_DROP_LEN_KINEMATIC:", _ARM_DROP_LEN_KINEMATIC);
+echo("  ARM_LEG_SHORTEN:", ARM_LEG_SHORTEN);
+echo("  PIVOT_HOLE_Z_FROM_BOTTOM:", PIVOT_HOLE_Z_FROM_BOTTOM);
 
 // Vector from Main Pivot to Bucket Pivot (For reference)
+// Use KINEMATIC leg length to keep arm rotation unchanged
 _bend_angle = 180 - ARM_ANGLE; // Note: ARM_ANGLE is now possibly obsolete if we use SHAPE_ANGLE
-_drop_vec_len = ARM_DROP_LEN + ARM_DROP_EXT - PIVOT_HOLE_X_FROM_FRONT; // Hole X position (from front edge)
+_drop_vec_len = _ARM_DROP_LEN_KINEMATIC + ARM_DROP_EXT - PIVOT_HOLE_X_FROM_FRONT; // Use kinematic length
 _tube_h = TUBE_2X6_1_4[1];
 _hole_z_offset = PIVOT_HOLE_Z_FROM_BOTTOM; // Hole Z position (from bottom edge)
 
 _dx = _drop_vec_len * cos(_bend_angle) + (_hole_z_offset - _tube_h) * sin(_bend_angle);
 _dz = -_drop_vec_len * sin(_bend_angle) + (_hole_z_offset - _tube_h) * cos(_bend_angle);
 
 // Calculate Tip Position (Top/Effective Pivot Point)
+// This uses kinematic leg length so arm angle stays the same
 ARM_TIP_X = (ARM_MAIN_LEN + ARM_OVERLAP) + _dx; // Removed +50 error
 ARM_TIP_Z = _tube_h + _dz;
 
@@ -363,8 +384,11 @@ echo("ARM_TIP_X =", ARM_TIP_X);
 echo("ARM_TIP_Z =", ARM_TIP_Z);
 
 // Calculate angles for kinematics
-_x_rel = ARM_TIP_X;
-_z_rel = ARM_TIP_Z - _tube_h/2;
+// Use ARM_TIP_X and ARM_TIP_Z directly - these represent the bucket pivot position
+// relative to the arm pivot in arm-local coordinates (before rotation)
+// Include BUCKET_PIVOT_Y_OFFSET to get actual bucket pivot position
+_x_rel = ARM_TIP_X + BUCKET_PIVOT_Y_OFFSET;
+_z_rel = ARM_TIP_Z;  // Fixed: removed _tube_h/2 offset to match bucket_attachment()
 
 _arm_eff_len = sqrt(pow(_x_rel, 2) + pow(_z_rel, 2));
 arm_alpha_calc = atan2(-_z_rel, _x_rel); // Angle below horizontal (positive value)
@@ -491,12 +515,20 @@ LIFT_CYL_BASE_Y = max(50, min(WHEEL_BASE/2, _calc_base_y + 10)); // Current logi
 //   We need to verify the pin-to-base distance.
 //   For now, we set BUCKET_LUG_OFFSET to this distance.
 //   Let's assume the lug height (base to pin center) is roughly 50mm (2").
-//   User Update: Shift bucket backwards closely to align pivot holes.
-BUCKET_LUG_OFFSET = 25; // Adjusted (35->25) to align pin with leg hole (Shift backwards)
-
-// Visual adjustment to shift bucket down without affecting kinematic target _T
-// Used to calibrate visual ground contact
-BUCKET_VISUAL_Z_OFFSET = -10;
+//   User Update: Shift bucket backwards to align pivot pin with arm leg hole.
+//   The U-channel lug (3x3 tube) outer back surface is at size/2 from pin center (after 90deg rotation)
+//   Lug back must be flush with bucket back plate (see DESIGN_RULES.md)
+//   Bucket back plate back face (Y=0 in bucket local) must align with lug outer back surface
+//   So BUCKET_LUG_OFFSET = size/2 makes lug outer back flush with bucket plate back face
+BUCKET_LUG_OFFSET = TUBE_3X3_1_4[0]/2; // 38.1mm: Lug outer back flush with bucket back plate back face
+
+// Note: BUCKET_PIVOT_Y_OFFSET is defined earlier in this file (after BUCKET_PIVOT_HEIGHT_FROM_BOTTOM)
+// to ensure arm kinematics calculations can account for it
+
+// Visual adjustment to shift bucket without affecting kinematic target _T
+// At BUCKET_VISUAL_Z_OFFSET = 0, bucket bottom should be exactly at ground (Z=0) when flat
+// Calculation: pivot_z(90) - (BUCKET_HEIGHT(450) - BUCKET_PIVOT_HEIGHT_FROM_BOTTOM(90)) = 0
+BUCKET_VISUAL_Z_OFFSET = 0; // Bucket bottom flat on ground
 BUCKET_BODY_Z_OFFSET = 0; // Keep bucket body aligned to pivot; use BUCKET_GROUND_CLEARANCE to set ground contact
 
 // Bucket Cylinder Mount Parameters