saltylab-firmware/chassis/saltytank_BOM.md

SaltyTank Chassis — BOM & Assembly Notes

Issue: #121 Agent: sl-mechanical Date: 2026-03-01

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Overview

SaltyTank is the tracked variant of the SaltyLab robot family. Rubber or metal continuous tracks replace wheels for rough-terrain capability. The electronics bay, RPLIDAR, D435i, stem, and sensor head are shared with SaltyLab and SaltyRover — no modifications required.

Side view (schematic):

    ←  +Y forward
                              Sensor head + RPLIDAR
                                      │
 ┌──────────────────────────── deck (Z=0) ───────────────────────────┐
 │              [Electronics Bay]     [Stem collar]                  │
 └──────────────────────────────────────────────────────────────────┘
 │ [Side frame - 90 mm tall]                                         │
 │   ◎ idler (Ø80)       ◎ road wheel  ◎ road wheel   ◎ drive (Ø66)│
 │───────────────────── track belt (rubber, 80 mm wide) ─────────────│
 (ground)

Top view (schematic):
            +Y (forward)
                 │
[track]  ┌──────┴───────┐  [track]
         │  [Electronics │
         │    Bay +      │
         │   RPLIDAR]    │
[track]  └──────┬───────┘  [track]
                │
            D435i →

Key dimensions:
  Deck: 500 mm (L) × 360 mm (W)
  Track belt centres: 360 + 6 + 80 = 446 mm left-right CL to CL
  Overall robot width (outer track edge): 446 + 80 = 526 mm
  Ground clearance (hull between tracks): 90 mm  ← exceeds 50 mm req.
  Height: deck to RPLIDAR scan plane: ~330 mm (with 550 mm stem option)

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File Index

File	Description	RENDER → Output
saltytank_chassis.scad	Deck plate + side frames + idler block + CSI/D435i mounts	See table below
saltytank_skid_plate.scad	Underside skid plate (bolt-on, sacrificial)	skid_2d → DXF; skid_stl → STL
rover_electronics_bay.scad	Electronics bay body + lid + RPLIDAR tower	Unchanged — reuse rover part
rover_motor_mount.scad	(Not used — drive sprockets mount directly to side frame)	—
rover_stem_adapter.scad	Stem adapter (shared)	Unchanged
rplidar_mount.scad	RPLIDAR anti-vibration ring (shared)	Unchanged

RENDER map

RENDER value	Output	Qty	Process
"deck_2d"	saltytank_deck.dxf	1	Waterjet / CNC, 8 mm Al
"side_frame_2d"	saltytank_side_frame.dxf	2	CNC / laser, 6 mm Al (cut 2×, flip 1)
"side_frame_stl"	saltytank_side_frame.stl	2	PETG print (prototype)
"idler_block_stl"	saltytank_idler_block.stl	2	PETG print
"csi_mount_stl"	saltytank_csi_mount.stl	4	PETG print
"d435i_mount_stl"	saltytank_d435i_mount.stl	1	PETG print
"skid_2d"	saltytank_skid.dxf	1	Waterjet / CNC, 4 mm HDPE
"skid_stl"	saltytank_skid.stl	1	PETG print (prototype)

Export commands

# Deck plate DXF:
openscad saltytank_chassis.scad    -D 'RENDER="deck_2d"'         -o saltytank_deck.dxf

# Side frame DXF (cut 2×, flip one):
openscad saltytank_chassis.scad    -D 'RENDER="side_frame_2d"'   -o saltytank_side_frame.dxf

# Side frame STL (print 2×, mirror right in slicer):
openscad saltytank_chassis.scad    -D 'RENDER="side_frame_stl"'  -o saltytank_side_frame.stl

# Idler tensioner block STL (×2):
openscad saltytank_chassis.scad    -D 'RENDER="idler_block_stl"' -o saltytank_idler_block.stl

# CSI bracket STL (×4):
openscad saltytank_chassis.scad    -D 'RENDER="csi_mount_stl"'   -o saltytank_csi_mount.stl

# D435i bracket STL (×1):
openscad saltytank_chassis.scad    -D 'RENDER="d435i_mount_stl"' -o saltytank_d435i_mount.stl

# Skid plate DXF (4 mm HDPE, preferred):
openscad saltytank_skid_plate.scad -D 'RENDER="skid_2d"'         -o saltytank_skid.dxf

# Skid plate STL (prototype):
openscad saltytank_skid_plate.scad -D 'RENDER="skid_stl"'        -o saltytank_skid.stl

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Part A — Deck Plate

#	Spec	Qty	Material	Process	Notes
A1	8 mm 5052-H32 Al, 500×360 mm blank	1	Aluminium	Waterjet	Preferred
A1-alt	6 mm 6061-T6 Al	1	—	CNC router	Saves 0.3 kg
A1-proto	8 mm PETG FDM, 2 halves lap-jointed	1	—	Print	Prototype only

Deck fasteners:

#	Spec	Qty	Use
A-f1	M5×20 SHCS	8	Side frame to deck side edge (4 per side)
A-f2	M5 T-nut or rivet nut	8	Captured in deck edge (installed before frame)
A-f3	M4×16 FHCS	4	Stem collar to deck (4× M4 countersunk)
A-f4	M3×12 SHCS	10	Electronics bay to deck
A-f5	M4×12 FHCS	6	Skid plate to deck (countersunk from below)
A-f6	M4 rivet-nut	6	Installed in deck for skid plate bolts

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Part B — Side Frames (×2)

#	RENDER	Qty	Material	Process	Notes
B1	side_frame_2d	2	6 mm 6061-T6 Al	CNC router or waterjet	Cut 2× same DXF; flip 1 (mirror)
B1-alt	side_frame_stl	2	PETG	Print	5 perims, 60% gyroid; prototype only

⚠ Hub motor flange bolt circle: Default is 52 mm BC × 4× M5. Measure your motor hub before cutting the side frame — adjust HUB_FLANGE_BC in saltytank_chassis.scad if needed.

Side frame fasteners:

#	Spec	Qty	Use
B-f1	M5×20 SHCS	8	Frame-to-deck attachment (4 per frame, through slotted holes)
B-f2	M5 nyloc	8	Under deck
B-f3	M5×16 SHCS	8	Hub motor flange to side frame (2× M5 per motor hub face)
B-f4	M8×60 hex bolt	2	Road wheel axle bolts (1 per wheel × 2 per side)
B-f5	M8 nyloc	4	Road wheel axle retention
B-f6	M8 flat washer	8	Both sides of each road wheel

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Part C — Drive Sprockets + Hub Motors

SaltyTank reuses the same hoverboard hub motors as SaltyLab/SaltyRover. A laser-cut sprocket plate bolts to the motor hub and engages the track belt.

#	Part	Qty	Spec	Notes
C1	Hub motor	2	10×2.125" tire, 36 V, ~350 W; axle OD 16.11 mm (caliper)	Only 2 motors — rear drive
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)
C3	Motor phase cable	2	12 AWG, 300 mm, XT30	Left + right rear
C4	Hall sensor cable	2	6-pin JST-PH, 300 mm	—

Sprocket plate design (separate file to be made if needed): 10 teeth, pitch = 20 mm → PCD = 20 / sin(18°) ≈ 64.7 mm → R ≈ 32.4 mm. Hub bolt circle = 52 mm, 4× M5 at 90°. Verify against actual motor hub. Sprocket tooth profile: ISO/DIN standard for roller chain or custom for belt track.

Motor fasteners:

#	Spec	Qty	Use
C-f1	M5×16 SHCS	8	Sprocket plate to motor hub flange (4 per sprocket)
C-f2	Hub motor axle nut	2	M16×1.5 (verify axle thread); torque 35–40 N·m
C-f3	Loctite 243	—	On axle nut and flange bolts

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Part D — Idler Wheels + Tensioners

#	RENDER	Qty	Material	Notes
D1	idler_block_stl	2	PETG	Tensioner sliding block, 1 per side

#	Part	Qty	Spec	Notes
D2	Idler wheel	2	Ø80 mm, 80+ mm wide, M8 bore, flanged	Off-shelf: e.g. polyurethane track idler
D3	M8×100 SHCS	2	Stainless	Idler axle through block + wheel + outer bearing
D4	M8 nyloc nut	2	—	Axle retention
D5	M8 flat washer	4	—	Both sides of idler wheel
D6	M6×40 SHCS	2	—	Tensioner adjustment bolt (threads into idler block lug)
D7	M6 nyloc nut	2	—	Captured in block; lock bolt position

Track tensioning procedure:

1. Loosen idler axle nut (M8) — block free to slide in slot.
2. Turn tensioner M6 bolt CW to push block rearward → tighten track.
3. Target: ~10 mm slack on upper track run (finger-press deflects 10 mm).
4. Tighten M8 axle nut to 12 N·m. Check tension after first 5-minute run.

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Part E — Road Wheels (2 per side, 4 total)

#	Part	Qty	Spec	Notes
E1	Road wheel	4	Ø60 mm × 80+ mm wide, M8 bore	Polyurethane or HDPE; must fit inside track width
E2	M8×80 SHCS	4	Stainless	Road wheel axle through side frame
E3	M8 nyloc	4	—	—
E4	M8 flat washer	8	—	—

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Part F — Track Belts

#	Part	Qty	Spec	Notes
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
F1-alt	Metal link track	2	80 mm wide, 20 mm pitch, adjustable length	Higher durability; heavier (~0.8 kg/belt); louder

Track circumference calculation: C = 2 × span + π × (D_sprocket + D_idler) / 2 = 2 × 440 + π × (66 + 80) / 2 = 880 + π × 73 = 880 + 229 ≈ 1109 mm Order 1120 mm (next standard rubber track pitch × N links).

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Part G — Skid Plate

#	RENDER	Qty	Material	Process	Notes
G1	skid_2d	1	4 mm HDPE (white)	Waterjet / CNC	Preferred — lightweight, low friction
G1-alt	skid_2d	1	2 mm 304 stainless	Laser-cut	Heavy but extreme durability
G1-proto	skid_stl	1	PETG	Print	Prototype — 2 halves if bed <500 mm

#	Spec	Qty	Use
G-f1	M4×12 FHCS	6	Skid plate to deck (countersunk flush)
G-f2	M4 rivet-nut (short)	6	Pre-installed in deck plate

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Part H — Sensor Brackets

#	RENDER	Qty	Material	Notes
H1	csi_mount_stl	4	PETG	CSI corner brackets (45° outward, 20° down)
H2	d435i_mount_stl	1	PETG	D435i front arm (8° nose-down)

#	Spec	Qty	Use
H-f1	M2×6 SHCS	8	CSI camera PCB to bracket
H-f2	M3×8 SHCS	8	CSI bracket to deck
H-f3	M4×14 SHCS	2	D435i bracket to deck front face
H-f4	1/4-20 UNC hex nut	1	Captured in D435i bracket face
H-c1	200 mm CSI FPC cable	4	IMX219 to Jetson

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Part I — Electronics Bay (reuse from rover)

The rover_electronics_bay.scad bay fits the SaltyTank deck directly — the deck bolt pattern is identical. Print or reuse existing bay + lid.

#	Part	Qty	Notes
I1	Electronics bay body	1	rover_electronics_bay.scad → bay_stl
I2	Electronics bay lid	1	Includes RPLIDAR tower
I3	M3×12 SHCS	10	Bay to deck
I4	M3×8 BHCS	4	Lid to bay

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Part J — Stem + Sensor Head (shared, unchanged)

Same stem adapter, RPLIDAR, D435i, and IMX219 sensor head as SaltyLab. Recommended stem length for SaltyTank: 500 mm (lower than SaltyBot mast for stability; RPLIDAR at ~635 mm from ground with 98 mm deck height).

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Mass Estimate — Frame Only

Assembly	Material	Est. mass
Deck plate (8 mm Al, ~45% lightened)	Al	~1.55 kg
Side frames ×2 (6 mm Al, ~35% lightened)	Al	~0.52 kg
Skid plate (4 mm HDPE, solid)	HDPE	~0.56 kg
Idler tensioner blocks ×2	PETG	~0.06 kg
CSI brackets ×4 + D435i bracket	PETG	~0.07 kg
Stem collar	PETG	~0.04 kg
Fasteners (M4–M8 SS)	Steel	~0.18 kg
Frame total		~2.98 kg ✓

Just under the 3 kg target. To save weight: switch side frames from 6 mm to 5 mm Al → saves ~0.09 kg. Set FRAME_T = 5.0 in saltytank_chassis.scad and re-export DXF.

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Assembly Sequence

1. Fabricate / source parts

1. Export DXFs; send deck and side frames to waterjet. Order HDPE skid to DXF.
2. Print idler blocks, CSI/D435i brackets, stem collar.
3. Source track belts, idler wheels, road wheels, hub motors.
4. Install M4 rivet-nuts in deck plate (6× for skid; stem flange positions).

2. Side frame preparation

1. Test-fit hub motor axle D-cut bore in side frame — adjust SPROCKET_AXLE_D and SPROCKET_AXLE_FLAT if caliper measurement differs.
2. Press or Loctite M8 flange nuts into road wheel axle positions (optional).

3. Frame assembly

1. Slide side frames into deck side edge slots (inner face flush with deck edge).
2. Insert M5×20 SHCS from above through deck slots; fit nyloc nuts under deck.
3. Snug only — leave adjustable for wheel alignment (step 6).

4. Drive motor installation

1. Feed hub motor axle through rear bore in side frame (D-cut aligned to flat).
2. Bolt sprocket plate to motor hub: 4× M5×16 SHCS, 2.5 N·m, Loctite 243.
3. Fit axle lock nut; Loctite 243; torque 35 N·m.
4. Route phase + hall cables through deck cable slot.

5. Road wheel installation

1. Slide M8×80 bolt through side frame road wheel bore.
2. Fit road wheel on axle (M8 flat washers both sides).
3. Thread M8 nyloc; torque to 12 N·m.
4. Verify wheel rotates freely.

6. Track belt installation (one side at a time)

1. Install idler block in tensioner slot (tensioner bolt only finger-tight).
2. Thread track belt around sprocket → road wheels → idler. (Easier with motor temporarily removed — reinstall after threading.)
3. Fit idler axle (M8×100) through idler block + idler wheel; nyloc finger-tight.
4. Apply tension: tighten M6 tensioner bolt until ~10 mm slack on upper run.
5. Torque idler axle nut to 12 N·m.

7. Geometry verification

1. Set robot on flat surface; check all 4 road wheels contact ground through track.
2. Measure track tension on both sides — should match within 2 mm.
3. Spin motors briefly — verify tracks run straight without walking.
4. Torque side-frame-to-deck M5 bolts to 4 N·m once alignment confirmed.

8. Skid plate

1. Slide skid plate under deck; align M4 countersunk holes with rivet-nuts.
2. Fasten 6× M4×12 FHCS from below; tighten evenly to 2.5 N·m.

9. Electronics, sensors, stem

1. Mount electronics bay on deck (10× M3×12); route cables.
2. Install CSI and D435i brackets on deck corners/front.
3. Press stem through collar; install stem adapter + clamp.
4. Mount sensor head + RPLIDAR on stem top.

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Critical Dimensions

Dimension	Nominal	Tolerance
Deck length × width	500 × 360 mm	±1 mm
Frame height	90 mm	±0.5 mm
Frame length	500 mm	±0.5 mm
Drive axle bore OD	16.11 mm	+0.4/0 (round section)
Drive axle flat chord	13.00 mm	+0.4/0
Bearing seat recess OD	37.80 mm	+1.5/0
Hub motor flange BC	52 mm	⚠ verify caliper
Tensioner slot height	10.5 mm	±0.2 mm
Tensioner travel	±15 mm	—
FC hole pattern	30.5×30.5 mm	±0.2 mm
Jetson hole pattern	58×49 mm	±0.2 mm
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

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OpenSCAD Version

Requires OpenSCAD 2021.01 or newer.

# Full assembly preview:
openscad saltytank_chassis.scad &