Fix frame tubes, add bolt holes, widen stiffener

Correct frame tube orientation and placement (rotate T1/T2 and adjust translations), add 1/2" bolt hole pattern for angle-iron mounts on front/rear tubes (24 holes each, drilled through Z faces), and widen the front stiffener center section to span motor plate outer edges. Adjust T3 arm crossbeam length to extend through inner arm CNC plates and update CROSS_BEAM_SPAN accordingly. Reshape inner wall plates to include a 5" flat front section and a smooth angled transition; update structural wrapper modules to pass new parameters and integrate rotated tubes in assembly. Files touched: lifetrac_v25.scad, parts/structural/tube_t1_front_frame.scad, tube_t2_rear_frame.scad, tube_t3_arm_crossbeam.scad, structural_parts.scad.

Author: dorkmo

LifeTrac-v25/AI NOTES/2026-02-03_Frame_Tubes_Stiffener_Updates.md

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+# LifeTrac v25 Frame Tubes and Stiffener Plate Updates
+**Date:** February 3, 2026
+
+## Summary
+This session focused on fixing frame tube placement, adding bolt holes for angle iron connections, widening the front stiffener plate, and reshaping the inner wall plates.
+
+---
+
+## Changes Made
+
+### 1. Frame Tube Rotation Fix
+**Files Modified:** `lifetrac_v25.scad`
+
+**Problem:** Frame tubes (T1 and T2) were misoriented - the 6" and 2" dimensions were swapped.
+
+**Solution:** Added `rotate([90, 0, 0])` to both frame tube placements in `cross_frame_tubes()` module. Also adjusted Y translation to compensate for the rotation shifting the tube position.
+
+```scad
+// Before:
+translate([0, FRONT_FRAME_TUBE_Y, FRAME_TUBE_Z])
+part_t1_front_frame_tube();
+
+// After:
+translate([0, FRONT_FRAME_TUBE_Y + FRAME_TUBE_WIDTH, FRAME_TUBE_Z])
+rotate([90, 0, 0])
+part_t1_front_frame_tube();
+```
+
+---
+
+### 2. Arm Crossbeam (T3) Length Adjustment
+**Files Modified:** 
+- `tube_t3_arm_crossbeam.scad`
+- `lifetrac_v25.scad`
+
+**Initial Change:** Shortened crossbeam to be flush with outer faces of inner arm CNC plates:
+```scad
+PART_T3_LENGTH = ARM_SPACING - TUBE_2X6_1_4[0] - 2*ARM_PLATE_THICKNESS;  // ~837mm
+```
+
+**Final Change:** Extended crossbeam through the arm CNC plates (user requested it reach through):
+```scad
+PART_T3_LENGTH = ARM_SPACING - TUBE_2X6_1_4[0];  // ~849mm
+```
+
+Also updated `CROSS_BEAM_SPAN` constant in main assembly to match.
+
+---
+
+### 3. Frame Tube Bolt Holes (T1 and T2)
+**Files Modified:**
+- `tube_t1_front_frame.scad`
+- `tube_t2_rear_frame.scad`
+- `structural_parts.scad`
+
+**Added bolt holes for angle iron mounts at 6 X positions:**
+1. Left outer panel
+2. Left inner panel
+3. Left motor plate
+4. Right motor plate
+5. Right inner panel
+6. Right outer panel
+
+**Hole Configuration:**
+- 24 holes per tube (6 positions × 2 faces × 2 holes per face)
+- 1/2" diameter bolts
+- Holes drilled through top and bottom Z faces (which become front/rear Y faces after rotation)
+- Y positions at ~50.8mm and ~101.6mm (matching angle iron hole spacing)
+
+**Key Fix:** Initial holes were too close to tube edges. Corrected by:
+- Drilling through Z faces instead of Y faces
+- Positioning holes along the 6" Y dimension (not the 2" Z dimension)
+
+**Motor Plate Alignment Fix:** Added `plate_thickness/2` offset to motor plate hole positions to match actual angle iron placement:
+```scad
+_left_motor_x = -(_track_width/2 - _sandwich_spacing/2) + _motor_plate_inboard + _motor_plate_thick/2;
+_right_motor_x = (_track_width/2 - _sandwich_spacing/2) - _motor_plate_inboard - _motor_plate_thick/2;
+```
+
+---
+
+### 4. Front Stiffener Plate Widening
+**Files Modified:** `lifetrac_v25.scad`
+
+**Change:** Extended the center (10") section from outer edge of left motor plate to outer edge of right motor plate.
+
+```scad
+// Before:
+translate([-MOTOR_PLATE_X, y_pos, z_start])
+cube([2*MOTOR_PLATE_X, plate_thickness, center_height]);
+
+// After:
+center_half_width = MOTOR_PLATE_X + MOTOR_PLATE_THICKNESS/2;
+translate([-center_half_width, y_pos, z_start])
+cube([2*center_half_width, plate_thickness, center_height]);
+```
+
+The outer 5" sections were also adjusted to start at the new center section edges.
+
+---
+
+### 5. Inner Wall Plate Reshaping
+**Files Modified:** `lifetrac_v25.scad`
+
+**Changes to `side_panel_left_inner()` and `side_panel_right_inner()`:**
+
+1. **Trimmed front section** beyond front stiffener plate position (`BOTTOM_PLATE_Y_END`)
+
+2. **Created flat 5" vertical section** at front, flush with front stiffener plate:
+   - Starts at `BOTTOM_PLATE_INNER_TRIM` (31.75mm)
+   - Height: 127mm (5")
+   - Matches outer section height of front stiffener plate
+
+3. **Angled continuation** from top of 5" section to existing slope line:
+   - Removes triangular section between flat top and original slope
+   - Creates smooth transition to upper panel profile
+
+```scad
+// Key parameters:
+flat_section_height = 127.0;  // 5" flat section at front
+flat_section_top = BOTTOM_PLATE_INNER_TRIM + flat_section_height;
+```
+
+---
+
+## Technical Notes
+
+### Coordinate System Reminder
+For frame tubes after `rotate([90, 0, 0])` in assembly:
+- Part Y (0 to 152.4mm) → World Z (height)
+- Part Z (0 to 50.8mm) → World -Y (depth)
+
+### Part Module Pattern
+- Individual part files use underscore-prefixed modules: `_part_xxx()`
+- `structural_parts.scad` provides wrapper modules: `part_xxx()`
+- Wrappers pass through parameters like `show_holes`
+
+### Hole Count Summary
+| Part | Holes | Description |
+|------|-------|-------------|
+| T1 Front Frame Tube | 24 | 6 positions × 2 faces × 2 holes |
+| T2 Rear Frame Tube | 24 | 6 positions × 2 faces × 2 holes |
+| T3 Arm Crossbeam | Existing | Via angle iron mounts |
+
+---
+
+## Files Modified
+- `lifetrac_v25.scad` - Main assembly
+- `parts/structural/tube_t1_front_frame.scad` - Front frame tube part
+- `parts/structural/tube_t2_rear_frame.scad` - Rear frame tube part
+- `parts/structural/tube_t3_arm_crossbeam.scad` - Arm crossbeam part
+- `parts/structural/structural_parts.scad` - Wrapper modules
+
+---
+
+## Part File Details
+
+### T1: Front Cross Frame Tube
+**File:** `parts/structural/tube_t1_front_frame.scad`
+
+**Material:** 2"×6"×1/4" Rectangular Tubing (50.8mm × 152.4mm × 6.35mm wall)
+
+**Quantity:** 1 piece
+
+**Dimensions:**
+- Length: `TRACK_WIDTH + SANDWICH_SPACING + 2*PANEL_THICKNESS + 2*12.7mm` (extends 1/2" past outer panels)
+- Width: 152.4mm (6")
+- Height: 50.8mm (2")
+
+**Bolt Holes Added:**
+- 24 total holes (6 X positions × 2 faces × 2 holes per position)
+- 1/2" diameter
+- Drilled through top and bottom faces (Z direction in part coords)
+- Y positions: ~50.8mm and ~101.6mm from edge
+
+**X Position Calculations:**
+```scad
+// Panel positions
+_left_outer_x = -(_track_width/2 + _sandwich_spacing/2);
+_left_inner_x = -(_track_width/2 - _sandwich_spacing/2) + _panel_thick;
+_right_inner_x = (_track_width/2 - _sandwich_spacing/2) - _panel_thick;
+_right_outer_x = (_track_width/2 + _sandwich_spacing/2);
+
+// Motor plate positions (with plate_thickness/2 offset)
+_left_motor_x = -(_track_width/2 - _sandwich_spacing/2) + _motor_plate_inboard + _motor_plate_thick/2;
+_right_motor_x = (_track_width/2 - _sandwich_spacing/2) - _motor_plate_inboard - _motor_plate_thick/2;
+
+// Hole X positions (1" inset from face toward center)
+PART_T1_HOLE_X = [
+    _left_outer_x + _angle_thick + _hole_inset,
+    _left_inner_x + _hole_inset,
+    _left_motor_x + _hole_inset,
+    _right_motor_x - _hole_inset,
+    _right_inner_x - _hole_inset,
+    _right_outer_x - _angle_thick - _hole_inset
+];
+```
+
+**Module Signature:**
+```scad
+module _part_t1_front_frame_tube(show_cutaway=false, show_holes=true)
+```
+
+---
+
+### T2: Rear Cross Frame Tube
+**File:** `parts/structural/tube_t2_rear_frame.scad`
+
+**Material:** 2"×6"×1/4" Rectangular Tubing (identical to T1)
+
+**Quantity:** 1 piece
+
+**Dimensions:** Same as T1
+
+**Bolt Holes:** Same pattern as T1 (24 holes)
+
+**Note:** Identical geometry to T1, positioned at rear wheel location in assembly.
+
+**Module Signature:**
+```scad
+module _part_t2_rear_frame_tube(show_cutaway=false, show_holes=true)
+```
+
+---
+
+### T3: Arm Crossbeam Tube
+**File:** `parts/structural/tube_t3_arm_crossbeam.scad`
+
+**Material:** 2"×6"×1/4" Rectangular Tubing
+
+**Quantity:** 1 piece
+
+**Length Calculation (Updated):**
+```scad
+// Crossbeam extends through inner arm CNC plates
+_arm_spacing = is_undef(ARM_SPACING) ? 900 : ARM_SPACING;
+_tube_w = is_undef(TUBE_2X6_1_4) ? 50.8 : TUBE_2X6_1_4[0];  // Arm tube width (2")
+
+// Ends flush with inner face of inner arm CNC plates
+PART_T3_LENGTH = _arm_spacing - _tube_w;  // ~849.2mm
+```
+
+**Previous Length:** `ARM_SPACING` (900mm) - was too long
+
+**Intermediate Length:** `ARM_SPACING - TUBE_2X6_1_4[0] - 2*ARM_PLATE_THICKNESS` (~836.5mm) - was too short
+
+**Final Length:** `ARM_SPACING - TUBE_2X6_1_4[0]` (~849.2mm) - extends through plates
+
+**Module Signature:**
+```scad
+module _part_t3_arm_crossbeam(show_holes=true)
+```
+
+---
+
+### Structural Parts Wrapper Updates
+**File:** `parts/structural/structural_parts.scad`
+
+**Updated wrapper modules to pass new parameters:**
+
+```scad
+// T1: Front Cross Frame Tube (1 pc)
+use <tube_t1_front_frame.scad>
+module part_t1_front_frame_tube(show_cutaway=false, show_holes=true) {
+    _part_t1_front_frame_tube(show_cutaway, show_holes);
+}
+
+// T2: Rear Cross Frame Tube (1 pc)
+use <tube_t2_rear_frame.scad>
+module part_t2_rear_frame_tube(show_cutaway=false, show_holes=true) {
+    _part_t2_rear_frame_tube(show_cutaway, show_holes);
+}
+```
+
+---
+
+## Assembly Integration
+
+### cross_frame_tubes() Module
+**Location:** `lifetrac_v25.scad`, lines ~3086-3105
+
+```scad
+module cross_frame_tubes() {
+    // Front frame tube (T1)
+    // Part module: length in X, origin at X=0 center, Y=0, Z=0 (bottom)
+    // Assembly needs: tube at Y=FRONT_FRAME_TUBE_Y, Z=FRAME_TUBE_Z
+    // Rotate to get 6" width in Y, 2" height in Z
+    translate([0, FRONT_FRAME_TUBE_Y + FRAME_TUBE_WIDTH, FRAME_TUBE_Z])
+    rotate([90, 0, 0])
+    part_t1_front_frame_tube();
+    
+    // Rear frame tube (T2)
+    translate([0, REAR_FRAME_TUBE_Y + FRAME_TUBE_WIDTH, FRAME_TUBE_Z])
+    rotate([90, 0, 0])
+    part_t2_rear_frame_tube();
+    
+    // Angle iron mounts (16 total: 2 per tube face × 4 wall panels × 2 tubes)
+    frame_tube_angle_irons();
+}
+```
+
+### CROSS_BEAM_SPAN Constant Update
+```scad
+// Cross beam span (extends through inner arm CNC plates)
+// Reduced by arm tube width (2") only - ends flush with inner face of plates
+CROSS_BEAM_SPAN = ARM_SPACING - TUBE_2X6_1_4[0];  // ~849mm
+```