sl-mechanical
d93919e26f
Three new chassis design files for the SaltyTank continuous-track variant: • saltytank_chassis.scad — Deck plate (500×360×8mm Al, DXF export), 2× side track frames (6mm Al, CNC/laser), idler tensioner sliding block, 4× CSI corner camera mounts (45°/20°), D435i front bracket (8° tilt), stem collar (Ø25mm shared). Drive sprocket mounts accept hoverboard hub motors with caliper-verified D-cut bore (16.11mm/13mm flat) + 52mm BC hub flange bolt pattern. M6 tensioner bolt adjusts idler ±15mm for track tension. Shared FC 30.5×30.5mm + Jetson 58×49mm M3 patterns. Electronics bay footprint matches rover_electronics_bay.scad exactly. • saltytank_skid_plate.scad — Sacrificial underside skid panel (360×500mm). 4mm HDPE (DXF) or PETG print; countersunk M4 FHCS bolt-on. 4× drain/ inspection slots; optional printed ribs (RIB_PRINT=true). Ground clearance of hull between tracks: 90mm (exceeds 50mm requirement). • saltytank_BOM.md — Full BOM: deck plate, side frames, drive sprockets, idler wheels + tensioners, road wheels (2/side), track belts (1109mm circumference calc), skid plate, sensor brackets, electronics bay (rover_electronics_bay.scad reused unchanged). Frame mass ≈ 2.98 kg (just under 3 kg target). Assembly sequence and track tensioning procedure included. Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
384 lines
15 KiB
Markdown
384 lines
15 KiB
Markdown
# SaltyTank Chassis — BOM & Assembly Notes
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**Issue: #121 Agent: sl-mechanical Date: 2026-03-01**
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---
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## Overview
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SaltyTank is the tracked variant of the SaltyLab robot family.
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Rubber or metal continuous tracks replace wheels for rough-terrain capability.
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The electronics bay, RPLIDAR, D435i, stem, and sensor head are **shared with
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SaltyLab and SaltyRover** — no modifications required.
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```
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Side view (schematic):
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← +Y forward
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Sensor head + RPLIDAR
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│
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┌──────────────────────────── deck (Z=0) ───────────────────────────┐
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│ [Electronics Bay] [Stem collar] │
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└──────────────────────────────────────────────────────────────────┘
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│ [Side frame - 90 mm tall] │
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│ ◎ idler (Ø80) ◎ road wheel ◎ road wheel ◎ drive (Ø66)│
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│───────────────────── track belt (rubber, 80 mm wide) ─────────────│
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(ground)
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Top view (schematic):
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+Y (forward)
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│
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[track] ┌──────┴───────┐ [track]
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│ [Electronics │
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│ Bay + │
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│ RPLIDAR] │
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[track] └──────┬───────┘ [track]
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│
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D435i →
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Key dimensions:
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Deck: 500 mm (L) × 360 mm (W)
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Track belt centres: 360 + 6 + 80 = 446 mm left-right CL to CL
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Overall robot width (outer track edge): 446 + 80 = 526 mm
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Ground clearance (hull between tracks): 90 mm ← exceeds 50 mm req.
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Height: deck to RPLIDAR scan plane: ~330 mm (with 550 mm stem option)
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```
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---
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## File Index
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| File | Description | RENDER → Output |
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|------|-------------|-----------------|
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| `saltytank_chassis.scad` | Deck plate + side frames + idler block + CSI/D435i mounts | See table below |
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| `saltytank_skid_plate.scad` | Underside skid plate (bolt-on, sacrificial) | `skid_2d` → DXF; `skid_stl` → STL |
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| `rover_electronics_bay.scad` | Electronics bay body + lid + RPLIDAR tower | **Unchanged** — reuse rover part |
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| `rover_motor_mount.scad` | (Not used — drive sprockets mount directly to side frame) | — |
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| `rover_stem_adapter.scad` | Stem adapter (shared) | Unchanged |
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| `rplidar_mount.scad` | RPLIDAR anti-vibration ring (shared) | Unchanged |
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### RENDER map
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| RENDER value | Output | Qty | Process |
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|---|---|---|---|
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| `"deck_2d"` | `saltytank_deck.dxf` | 1 | Waterjet / CNC, 8 mm Al |
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| `"side_frame_2d"` | `saltytank_side_frame.dxf` | 2 | CNC / laser, 6 mm Al (cut 2×, flip 1) |
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| `"side_frame_stl"` | `saltytank_side_frame.stl` | 2 | PETG print (prototype) |
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| `"idler_block_stl"` | `saltytank_idler_block.stl` | 2 | PETG print |
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| `"csi_mount_stl"` | `saltytank_csi_mount.stl` | 4 | PETG print |
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| `"d435i_mount_stl"` | `saltytank_d435i_mount.stl` | 1 | PETG print |
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| `"skid_2d"` | `saltytank_skid.dxf` | 1 | Waterjet / CNC, 4 mm HDPE |
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| `"skid_stl"` | `saltytank_skid.stl` | 1 | PETG print (prototype) |
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### Export commands
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```bash
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# Deck plate DXF:
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openscad saltytank_chassis.scad -D 'RENDER="deck_2d"' -o saltytank_deck.dxf
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# Side frame DXF (cut 2×, flip one):
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openscad saltytank_chassis.scad -D 'RENDER="side_frame_2d"' -o saltytank_side_frame.dxf
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# Side frame STL (print 2×, mirror right in slicer):
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openscad saltytank_chassis.scad -D 'RENDER="side_frame_stl"' -o saltytank_side_frame.stl
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# Idler tensioner block STL (×2):
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openscad saltytank_chassis.scad -D 'RENDER="idler_block_stl"' -o saltytank_idler_block.stl
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# CSI bracket STL (×4):
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openscad saltytank_chassis.scad -D 'RENDER="csi_mount_stl"' -o saltytank_csi_mount.stl
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# D435i bracket STL (×1):
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openscad saltytank_chassis.scad -D 'RENDER="d435i_mount_stl"' -o saltytank_d435i_mount.stl
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# Skid plate DXF (4 mm HDPE, preferred):
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openscad saltytank_skid_plate.scad -D 'RENDER="skid_2d"' -o saltytank_skid.dxf
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# Skid plate STL (prototype):
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openscad saltytank_skid_plate.scad -D 'RENDER="skid_stl"' -o saltytank_skid.stl
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```
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---
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## Part A — Deck Plate
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| # | Spec | Qty | Material | Process | Notes |
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|---|------|-----|----------|---------|-------|
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| A1 | 8 mm 5052-H32 Al, 500×360 mm blank | 1 | Aluminium | Waterjet | Preferred |
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| A1-alt | 6 mm 6061-T6 Al | 1 | — | CNC router | Saves 0.3 kg |
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| A1-proto | 8 mm PETG FDM, 2 halves lap-jointed | 1 | — | Print | Prototype only |
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**Deck fasteners:**
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| # | Spec | Qty | Use |
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|---|------|-----|-----|
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| A-f1 | M5×20 SHCS | 8 | Side frame to deck side edge (4 per side) |
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| A-f2 | M5 T-nut or rivet nut | 8 | Captured in deck edge (installed before frame) |
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| A-f3 | M4×16 FHCS | 4 | Stem collar to deck (4× M4 countersunk) |
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| A-f4 | M3×12 SHCS | 10 | Electronics bay to deck |
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| A-f5 | M4×12 FHCS | 6 | Skid plate to deck (countersunk from below) |
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| A-f6 | M4 rivet-nut | 6 | Installed in deck for skid plate bolts |
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---
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## Part B — Side Frames (×2)
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| # | RENDER | Qty | Material | Process | Notes |
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|---|--------|-----|----------|---------|-------|
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| B1 | `side_frame_2d` | 2 | 6 mm 6061-T6 Al | CNC router or waterjet | Cut 2× same DXF; flip 1 (mirror) |
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| B1-alt | `side_frame_stl` | 2 | PETG | Print | 5 perims, 60% gyroid; prototype only |
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> ⚠ **Hub motor flange bolt circle:** Default is 52 mm BC × 4× M5.
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> **Measure your motor hub** before cutting the side frame — adjust `HUB_FLANGE_BC`
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> in `saltytank_chassis.scad` if needed.
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**Side frame fasteners:**
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| # | Spec | Qty | Use |
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|---|------|-----|-----|
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| B-f1 | M5×20 SHCS | 8 | Frame-to-deck attachment (4 per frame, through slotted holes) |
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| B-f2 | M5 nyloc | 8 | Under deck |
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| B-f3 | M5×16 SHCS | 8 | Hub motor flange to side frame (2× M5 per motor hub face) |
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| B-f4 | M8×60 hex bolt | 2 | Road wheel axle bolts (1 per wheel × 2 per side) |
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| B-f5 | M8 nyloc | 4 | Road wheel axle retention |
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| B-f6 | M8 flat washer | 8 | Both sides of each road wheel |
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---
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## Part C — Drive Sprockets + Hub Motors
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SaltyTank reuses the same hoverboard hub motors as SaltyLab/SaltyRover.
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A laser-cut sprocket plate bolts to the motor hub and engages the track belt.
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| # | Part | Qty | Spec | Notes |
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|---|------|-----|------|-------|
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| C1 | Hub motor | 2 | 10×2.125" tire, 36 V, ~350 W; axle OD 16.11 mm (caliper) | **Only 2 motors — rear drive** |
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| C2 | Drive sprocket plate | 2 | 5 mm 6061-T6 Al, laser-cut | 10-tooth, 20 mm pitch, PCD ≈ 64.7 mm; Ø52 mm hub bolt holes (verify) |
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| C3 | Motor phase cable | 2 | 12 AWG, 300 mm, XT30 | Left + right rear |
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| C4 | Hall sensor cable | 2 | 6-pin JST-PH, 300 mm | — |
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> **Sprocket plate design** (separate file to be made if needed):
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> 10 teeth, pitch = 20 mm → PCD = 20 / sin(18°) ≈ 64.7 mm → R ≈ 32.4 mm.
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> Hub bolt circle = 52 mm, 4× M5 at 90°. Verify against actual motor hub.
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> Sprocket tooth profile: ISO/DIN standard for roller chain or custom for belt track.
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**Motor fasteners:**
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| # | Spec | Qty | Use |
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|---|------|-----|-----|
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| C-f1 | M5×16 SHCS | 8 | Sprocket plate to motor hub flange (4 per sprocket) |
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| C-f2 | Hub motor axle nut | 2 | M16×1.5 (verify axle thread); torque 35–40 N·m |
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| C-f3 | Loctite 243 | — | On axle nut and flange bolts |
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---
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## Part D — Idler Wheels + Tensioners
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| # | RENDER | Qty | Material | Notes |
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|---|--------|-----|----------|-------|
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| D1 | `idler_block_stl` | 2 | PETG | Tensioner sliding block, 1 per side |
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| # | Part | Qty | Spec | Notes |
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|---|------|-----|------|-------|
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| D2 | Idler wheel | 2 | Ø80 mm, 80+ mm wide, M8 bore, flanged | Off-shelf: e.g. polyurethane track idler |
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| D3 | M8×100 SHCS | 2 | Stainless | Idler axle through block + wheel + outer bearing |
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| D4 | M8 nyloc nut | 2 | — | Axle retention |
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| D5 | M8 flat washer | 4 | — | Both sides of idler wheel |
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| D6 | M6×40 SHCS | 2 | — | Tensioner adjustment bolt (threads into idler block lug) |
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| D7 | M6 nyloc nut | 2 | — | Captured in block; lock bolt position |
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**Track tensioning procedure:**
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1. Loosen idler axle nut (M8) — block free to slide in slot.
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2. Turn tensioner M6 bolt CW to push block rearward → tighten track.
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3. Target: ~10 mm slack on upper track run (finger-press deflects 10 mm).
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4. Tighten M8 axle nut to 12 N·m. Check tension after first 5-minute run.
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---
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## Part E — Road Wheels (2 per side, 4 total)
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| # | Part | Qty | Spec | Notes |
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|---|------|-----|------|-------|
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| E1 | Road wheel | 4 | Ø60 mm × 80+ mm wide, M8 bore | Polyurethane or HDPE; must fit inside track width |
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| E2 | M8×80 SHCS | 4 | Stainless | Road wheel axle through side frame |
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| E3 | M8 nyloc | 4 | — | — |
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| E4 | M8 flat washer | 8 | — | — |
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---
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## Part F — Track Belts
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| # | Part | Qty | Spec | Notes |
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|---|------|-----|------|-------|
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| F1 | Rubber track belt | 2 | 80 mm wide, 20 mm pitch, ~1040 mm circumference | Circumference: 2 × (sprocket–idler CL) + π × (sprocket_D + idler_D)/2 ≈ 2 × 440 + π × 72 ≈ 1106 mm; order next standard size up |
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| F1-alt | Metal link track | 2 | 80 mm wide, 20 mm pitch, adjustable length | Higher durability; heavier (~0.8 kg/belt); louder |
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> **Track circumference calculation:**
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> `C = 2 × span + π × (D_sprocket + D_idler) / 2`
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> ` = 2 × 440 + π × (66 + 80) / 2`
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> ` = 880 + π × 73`
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> ` = 880 + 229 ≈ 1109 mm`
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> Order **1120 mm** (next standard rubber track pitch × N links).
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---
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## Part G — Skid Plate
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| # | RENDER | Qty | Material | Process | Notes |
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|---|--------|-----|----------|---------|-------|
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| G1 | `skid_2d` | 1 | 4 mm HDPE (white) | Waterjet / CNC | Preferred — lightweight, low friction |
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| G1-alt | `skid_2d` | 1 | 2 mm 304 stainless | Laser-cut | Heavy but extreme durability |
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| G1-proto | `skid_stl` | 1 | PETG | Print | Prototype — 2 halves if bed <500 mm |
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| # | Spec | Qty | Use |
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|---|------|-----|-----|
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| G-f1 | M4×12 FHCS | 6 | Skid plate to deck (countersunk flush) |
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| G-f2 | M4 rivet-nut (short) | 6 | Pre-installed in deck plate |
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---
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## Part H — Sensor Brackets
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| # | RENDER | Qty | Material | Notes |
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|---|--------|-----|----------|-------|
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| H1 | `csi_mount_stl` | 4 | PETG | CSI corner brackets (45° outward, 20° down) |
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| H2 | `d435i_mount_stl` | 1 | PETG | D435i front arm (8° nose-down) |
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| # | Spec | Qty | Use |
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|---|------|-----|-----|
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| H-f1 | M2×6 SHCS | 8 | CSI camera PCB to bracket |
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| H-f2 | M3×8 SHCS | 8 | CSI bracket to deck |
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| H-f3 | M4×14 SHCS | 2 | D435i bracket to deck front face |
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| H-f4 | 1/4-20 UNC hex nut | 1 | Captured in D435i bracket face |
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| H-c1 | 200 mm CSI FPC cable | 4 | IMX219 to Jetson |
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---
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## Part I — Electronics Bay (reuse from rover)
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The `rover_electronics_bay.scad` bay fits the SaltyTank deck directly — the
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deck bolt pattern is identical. Print or reuse existing bay + lid.
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| # | Part | Qty | Notes |
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|---|------|-----|-------|
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| I1 | Electronics bay body | 1 | `rover_electronics_bay.scad` → `bay_stl` |
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| I2 | Electronics bay lid | 1 | Includes RPLIDAR tower |
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| I3 | M3×12 SHCS | 10 | Bay to deck |
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| I4 | M3×8 BHCS | 4 | Lid to bay |
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---
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## Part J — Stem + Sensor Head (shared, unchanged)
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Same stem adapter, RPLIDAR, D435i, and IMX219 sensor head as SaltyLab.
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Recommended stem length for SaltyTank: **500 mm** (lower than SaltyBot mast for
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stability; RPLIDAR at ~635 mm from ground with 98 mm deck height).
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---
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## Mass Estimate — Frame Only
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| Assembly | Material | Est. mass |
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|----------|----------|-----------|
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| Deck plate (8 mm Al, ~45% lightened) | Al | ~1.55 kg |
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| Side frames ×2 (6 mm Al, ~35% lightened) | Al | ~0.52 kg |
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| Skid plate (4 mm HDPE, solid) | HDPE | ~0.56 kg |
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| Idler tensioner blocks ×2 | PETG | ~0.06 kg |
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| CSI brackets ×4 + D435i bracket | PETG | ~0.07 kg |
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| Stem collar | PETG | ~0.04 kg |
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| Fasteners (M4–M8 SS) | Steel | ~0.18 kg |
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| **Frame total** | | **~2.98 kg** ✓ |
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> **Just under the 3 kg target.**
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> To save weight: switch side frames from 6 mm to 5 mm Al → saves ~0.09 kg.
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> Set `FRAME_T = 5.0` in `saltytank_chassis.scad` and re-export DXF.
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---
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## Assembly Sequence
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### 1. Fabricate / source parts
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1. Export DXFs; send deck and side frames to waterjet. Order HDPE skid to DXF.
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2. Print idler blocks, CSI/D435i brackets, stem collar.
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3. Source track belts, idler wheels, road wheels, hub motors.
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4. Install M4 rivet-nuts in deck plate (6× for skid; stem flange positions).
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### 2. Side frame preparation
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1. Test-fit hub motor axle D-cut bore in side frame — adjust `SPROCKET_AXLE_D`
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and `SPROCKET_AXLE_FLAT` if caliper measurement differs.
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2. Press or Loctite M8 flange nuts into road wheel axle positions (optional).
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### 3. Frame assembly
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1. Slide side frames into deck side edge slots (inner face flush with deck edge).
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2. Insert M5×20 SHCS from above through deck slots; fit nyloc nuts under deck.
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3. **Snug only** — leave adjustable for wheel alignment (step 6).
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### 4. Drive motor installation
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1. Feed hub motor axle through rear bore in side frame (D-cut aligned to flat).
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2. Bolt sprocket plate to motor hub: 4× M5×16 SHCS, 2.5 N·m, Loctite 243.
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3. Fit axle lock nut; Loctite 243; torque 35 N·m.
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4. Route phase + hall cables through deck cable slot.
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### 5. Road wheel installation
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1. Slide M8×80 bolt through side frame road wheel bore.
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2. Fit road wheel on axle (M8 flat washers both sides).
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3. Thread M8 nyloc; torque to 12 N·m.
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4. Verify wheel rotates freely.
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### 6. Track belt installation (one side at a time)
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1. Install idler block in tensioner slot (tensioner bolt only finger-tight).
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2. Thread track belt around sprocket → road wheels → idler.
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*(Easier with motor temporarily removed — reinstall after threading.)*
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3. Fit idler axle (M8×100) through idler block + idler wheel; nyloc finger-tight.
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4. Apply tension: tighten M6 tensioner bolt until ~10 mm slack on upper run.
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5. Torque idler axle nut to 12 N·m.
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### 7. Geometry verification
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1. Set robot on flat surface; check all 4 road wheels contact ground through track.
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2. Measure track tension on both sides — should match within 2 mm.
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3. Spin motors briefly — verify tracks run straight without walking.
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4. Torque side-frame-to-deck M5 bolts to 4 N·m once alignment confirmed.
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### 8. Skid plate
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1. Slide skid plate under deck; align M4 countersunk holes with rivet-nuts.
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2. Fasten 6× M4×12 FHCS from below; tighten evenly to 2.5 N·m.
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### 9. Electronics, sensors, stem
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1. Mount electronics bay on deck (10× M3×12); route cables.
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2. Install CSI and D435i brackets on deck corners/front.
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3. Press stem through collar; install stem adapter + clamp.
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4. Mount sensor head + RPLIDAR on stem top.
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---
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## Critical Dimensions
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| Dimension | Nominal | Tolerance |
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|-----------|---------|-----------|
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| Deck length × width | 500 × 360 mm | ±1 mm |
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| Frame height | 90 mm | ±0.5 mm |
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| Frame length | 500 mm | ±0.5 mm |
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| Drive axle bore OD | 16.11 mm | +0.4/0 (round section) |
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| Drive axle flat chord | 13.00 mm | +0.4/0 |
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| Bearing seat recess OD | 37.80 mm | +1.5/0 |
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| Hub motor flange BC | 52 mm | **⚠ verify caliper** |
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| Tensioner slot height | 10.5 mm | ±0.2 mm |
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| Tensioner travel | ±15 mm | — |
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| FC hole pattern | 30.5×30.5 mm | ±0.2 mm |
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| Jetson hole pattern | 58×49 mm | ±0.2 mm |
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| Stem bore | Ø25.5 mm | +0.3/0 |
|
||
| Track belt width | 80 mm | ±1 mm |
|
||
| Sprocket PCD | 64.7 mm | ±0.5 mm |
|
||
| Idler OD | 80 mm | ±1 mm |
|
||
| Road wheel OD | 60 mm | ±1 mm |
|
||
|
||
---
|
||
|
||
## OpenSCAD Version
|
||
|
||
Requires OpenSCAD **2021.01 or newer**.
|
||
|
||
```bash
|
||
# Full assembly preview:
|
||
openscad saltytank_chassis.scad &
|
||
```
|