Refactor lift cylinder mount calculations for leverage

Reworked the lift cylinder base Y and Z position calculations to optimize leverage at the lowest arm position. The new approach computes attachment points based on arm geometry, axle clearance, and desired cylinder angle, improving clarity and maintainability.

Author: dorkmo

LifeTrac-v25/mechanical_design/openscad/lifetrac_v25.scad

@@ -232,10 +232,33 @@ BUCKET_TILT_ANGLE = BUCKET_GROUND_TILT + (animation_phase * (BUCKET_MAX_CURL - B
 // =============================================================================
 
 // Lift cylinder mounting points (arms pivot at rear, cylinders attach forward)
-LIFT_CYL_BASE_Y = WHEEL_BASE * 0.5;          // Base mount Y position (forward of pivot)
-LIFT_CYL_BASE_Z = FRAME_Z_OFFSET + MACHINE_HEIGHT * 0.4;      // Base mount Z position
+// Optimized for leverage at bottom position (cylinder pushes up/forward from low rear point)
+
+// 1. Define Arm Attachment Point
 LIFT_CYL_ARM_OFFSET = ARM_LENGTH * 0.25;     // Attachment point along arm from pivot (proportional)
 
+// 2. Calculate Arm Attachment Position in World Coords at Lowest Angle (Bucket on Ground)
+//    Pivot is at [0, ARM_PIVOT_Y, ARM_PIVOT_Z]
+_theta_min = -ARM_GROUND_ANGLE;
+_attach_y_world = ARM_PIVOT_Y + LIFT_CYL_ARM_OFFSET * cos(_theta_min);
+_attach_z_world = ARM_PIVOT_Z + LIFT_CYL_ARM_OFFSET * sin(_theta_min);
+
+// 3. Determine Base Z Height (Constrained by Axle Clearance)
+//    Must clear the rear axle (FRAME_Z_OFFSET + WHEEL_DIAMETER/2)
+_min_base_z = FRAME_Z_OFFSET + WHEEL_DIAMETER/2 + 80; // 80mm clearance
+LIFT_CYL_BASE_Z = _min_base_z;
+
+// 4. Calculate Base Y for Optimal Leverage Angle
+//    We want the cylinder to push at an angle ~45-50 degrees from horizontal
+//    to be roughly perpendicular to the arm (which is at ~-45 degrees).
+//    Slope m = tan(target_angle).
+//    Y = Attach_Y - (Attach_Z - Base_Z) / m
+_target_cyl_angle = 50; // Degrees
+_calc_base_y = _attach_y_world - (_attach_z_world - LIFT_CYL_BASE_Z) / tan(_target_cyl_angle);
+
+// 5. Clamp Y to valid frame range (0 to WHEEL_BASE/2)
+LIFT_CYL_BASE_Y = max(50, min(WHEEL_BASE/2, _calc_base_y));
+
 // Bucket cylinder mounting points
 // Cylinders now attach to the cross beam instead of individual arms
 BUCKET_CYL_ARM_POS = CROSS_BEAM_1_POS;       // Mount at cross beam position