ARACHNE-001: Forearm Slingshot Launcher
Classification: Wearable Elastic Propulsion
Status: DRAFT v0.1
Date: 2026-01-22
1. CONCEPT OVERVIEW
FOREARM SLINGSHOT - "ARACHNE LAUNCHER"
═══════════════════════════════════════
ELBOW VERTEX (Anchor Point)
┌───────────────────────────────────────────────────────────────────┐
│ │
│ ╔═══╗ │
│ ║ ◉ ║ ← Elbow mount (elastic anchor + tensioner) │
│ ╚═╤═╝ │
│ │ │
│ │ ══════════════════════════════════════ │
│ │ ║ ELASTIC BAND (high-tension latex) ║ │
│ │ ══════════════════════════════════════ │
│ │ │ │
│ │ F O R E A R M R U N W A Y │
│ │ │ │
│ ▼ ▼ │
│ ┌─────────────────────────────────────────┐ │
│ │▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓│ ← Forearm sleeve │
│ │▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓│ (guides elastic) │
│ └─────────────────────────────────────────┘ │
│ │ │
│ ▼ │
│ ╔═══════════════════╗ │
│ ║ WRIST COIL UNIT ║ ← Spring-loaded spool │
│ ║ ┌───┐ ┌───┐ ║ (stores elastic tension) │
│ ║ │ ◎ │──│ ◎ │ ║ (uncoils at MACH release) │
│ ║ └───┘ └───┘ ║ │
│ ╚════════╤══════════╝ │
│ │ │
│ ▼ │
│ ┌───────────────────────────────────────────────┐ │
│ │ BACK OF HAND │ │
│ │ ╔═══════════════════╗ │ │
│ │ ║ SPRINGBOARD ║ ← Launch ramp │ │
│ │ ║ ▲▲▲▲▲▲▲▲▲▲▲▲▲ ║ (curved for │ │
│ │ ║ / \ ║ trajectory) │ │
│ │ ╚═══════════════════╝ │ │
│ │ │ │ │
│ └─────────────────┼─────────────────────────────┘ │
│ │ │
│ ┌─────────────────┼─────────────────────────────────┐ │
│ │ T H U M B │ T R I G G E R │ │
│ │ ▼ │ │
│ │ ┌─────────────┐ │ │
│ │ │ ◉ LATCH ◉ │ ← Thumb holds elastic │ │
│ │ │ ╲ ╱ │ at tension vertex │ │
│ │ │ ╲ ╱ │ │ │
│ │ │ ╲ ╱ │ RELEASE = thumb lifts │ │
│ │ │ V │ → elastic snaps back │ │
│ │ └─────────────┘ │ │
│ └───────────────────────────────────────────────────┘ │
│ │
└───────────────────────────────────────────────────────────────────┘
2. LAUNCH SEQUENCE
Phase 1: ARMED
[ELBOW]
║
║←─────────────────────┐
║ elastic stretched │
║ (potential energy) │
║ │
[WRIST] │
║ coiled tight │
║ │
[HAND] │
║ │
[THUMB]═══════════════════┘
↑
LATCHED (vertex)
Phase 2: RELEASE
[ELBOW]
║
║ ←──── elastic SNAPS
║ (kinetic energy)
║
[WRIST]
║ UNCOILS → MACH WAVE
║
[HAND]
║
[THUMB] ← released
Phase 3: TUNNEL ACCELERATION
Elastic wave propagates through wrist coil at supersonic speed:
════►════►════►
MACH WAVE
Phase 4: SPRINGBOARD LAUNCH
Projectile hits curved ramp on back of hand, redirects trajectory:
╱ ↗ PROJECTILE
╱
═════╱ springboard
↖ incoming wave
3. COMPONENT SPECIFICATIONS
3.1 Elbow Anchor Assembly
| Component |
Material |
Dimensions |
Notes |
| Mount plate |
Aluminum 6061-T6 |
60mm × 40mm × 3mm |
Anodized |
| Elastic hook |
Stainless 316 |
8mm diameter |
Polished loop |
| Strap |
Neoprene + Velcro |
Adjustable |
Silicone grip lining |
| Tensioner |
Spring steel |
2mm wire |
Preload adjustment |
Load Rating: 150N static, 300N dynamic
3.2 Forearm Runway Sleeve
| Component |
Material |
Dimensions |
Notes |
| Outer shell |
Ripstop nylon |
250mm length |
Low friction |
| Inner channel |
PTFE tube |
12mm ID |
Guides elastic |
| Reinforcement |
Carbon fiber strips |
3mm × 200mm |
Prevents twist |
3.3 Wrist Coil Unit
┌──────────────────────┐
│ SPRING HOUSING │
│ ┌────────────────┐ │
│ │ ╭──────────╮ │ │
│ │ │ ◎◎◎◎◎◎◎◎ │ │ │ ← Coiled elastic
│ │ │ ◎◎◎◎◎◎◎◎ │ │ │ (compressed spiral)
│ │ ╰──────────╯ │ │
│ └───────┬────────┘ │
│ │ │
│ ════╧════ │ ← Release channel
│ (MACH TUNNEL) │
└──────────────────────┘
| Component |
Material |
Dimensions |
Notes |
| Housing |
Glass-filled nylon |
50mm × 30mm × 20mm |
Injection molded |
| Spool core |
Delrin |
25mm diameter |
Low friction |
| Spring |
Music wire |
0.8mm × 15 coils |
2N/mm rate |
| Channel |
Polished steel tube |
8mm ID |
Chrome lined |
3.4 Springboard (Back of Hand)
| Component |
Material |
Dimensions |
Notes |
| Ramp surface |
Flex-polymer (TPU) |
80mm × 50mm |
15° curve |
| Base plate |
Carbon fiber |
2mm thickness |
Bonded to glove |
| Shock absorber |
Silicone gel pad |
5mm thickness |
Dampens impact |
3.5 Thumb Trigger
| Component |
Material |
Dimensions |
Notes |
| Latch body |
Titanium |
20mm × 15mm |
Lightweight |
| Release mechanism |
Ball detent |
3mm ball |
10N release force |
| Thumb pad |
Textured rubber |
15mm diameter |
Ergonomic |
4. ELASTIC SPECIFICATIONS
Primary Band
- Material: Natural latex surgical tubing
- Dimensions: 6mm OD × 3mm ID × 400mm length
- Elongation: 600% max
- Tensile strength: 25 MPa
- Fatigue life: ~5000 cycles at 300% stretch
Reinforcement (at vertices)
- Material: Kevlar sleeve
- Coverage: 30mm at each anchor point
- Purpose: Prevent abrasion failure
5. PERFORMANCE ESTIMATES
| Parameter |
Value |
Notes |
| Draw length |
300mm |
Elbow to thumb |
| Draw force |
50-80N |
User adjustable |
| Stored energy |
7-12 J |
At full draw |
| Projectile mass |
5-20g |
Foam darts, etc. |
| Launch velocity |
25-40 m/s |
90-145 km/h |
| Effective range |
15-30m |
Flat trajectory |
6. ERGONOMICS & FIT
Sizing Chart
| Size |
Forearm Length |
Wrist Circumference |
| S |
220-250mm |
140-160mm |
| M |
250-280mm |
160-180mm |
| L |
280-310mm |
180-200mm |
| XL |
310-340mm |
200-220mm |
Fit Concerns & Solutions
| Concern |
Risk |
Solution |
| Elbow anchor slip |
Misfire |
Velcro + silicone grip |
| Wrist coil bulk |
Discomfort |
Low-profile spiral housing |
| Thumb fatigue |
Strain injury |
Mechanical latch (click-release) |
| Back-of-hand impact |
Bruising |
Flex-polymer springboard |
| Elastic wear at vertices |
Failure |
Kevlar reinforcement |
Fit Rating
HAND-FIT RATING: ████████░░ 8/10
(Prototype viable, needs iteration on wrist bulk)
7. SAFETY WARNINGS
⚠️ EYE PROTECTION REQUIRED - Always wear safety glasses
⚠️ ELASTIC INSPECTION - Check for cracks/wear before each use
⚠️ NEVER DRY FIRE - Always have projectile loaded
⚠️ TEMPERATURE LIMITS - Latex degrades below 0°C and above 40°C
⚠️ FINGER CLEARANCE - Keep fingers clear of release channel
8. REVISION HISTORY
| Version |
Date |
Changes |
| 0.1 |
2026-01-22 |
Initial draft |
9. RELATED DESIGNS
- ARACHNE-002: Dual-arm synchronized launcher (PLANNED)
- ARACHNE-003: Magnetic assist variant (PLANNED)
- ARACHNE-004: Compressed gas hybrid (PLANNED)
10. CROSS-REFERENCE: MARIONETTE SPOOL SYSTEM
The ARACHNE forearm launcher shares architectural DNA with the MARIONETTE SPOOL
sail-drone propulsion system (src/physics/marionette_spool.py).
Shared Principles
| Principle |
ARACHNE |
MARIONETTE |
| Tether Energy Storage |
Elastic band on wrist coil |
Cables wound on spool drums |
| Release Mechanism |
Thumb latch (vertex) |
Centrifugal unreeling |
| Runway/Guide |
Forearm sleeve |
Cable channels per sail |
| Human Control Point |
Thumb trigger |
Throw + whistle command |
| Terminal Guidance |
Springboard redirect |
Champion brain + HOLD |
MARIONETTE SPOOL Architecture
COLLAPSED (pre-throw) DEPLOYED (marionette mode)
┌───────┐ SAILS
│███████│ ⛵ ⛵
│███████│◄── All cables \ /
│███████│ wound tight \ /
│SPOOL │ ┌───┴───┐
└───────┘ │ SPOOL │◄── Champion brain
│ │CONTROL│ runs HERE
▼ └───┬───┘
Human │
hand individual
cable control
Integration Concept: ARACHNE-MARIONETTE Hybrid
The ARACHNE launcher could serve as the throw mechanism for a MARIONETTE spool:
- Pre-throw: SPOOL is wound, cables coiled
- ARACHNE Launch: Forearm runway provides velocity + spin to spool
- Unraveling: Centrifugal force deploys sails
- Marionette Mode: Champion brain takes over cable control
- Recall: Sails collapse, cables reel back to spool
FOREARM ──────────────────────────────────► DEPLOYED CONSTELLATION
[ELBOW] ⛵
║ ⛵ ╲ ╱ ⛵
║══elastic══[WRIST]══SPOOL══════throw══════► ╲│╱
║ [SPOOL]
[THUMB] │
↑ MARIONETTE
release CONTROL
Source References
src/physics/marionette_spool.py - Spool mechanism + Champion brain integrationsrc/visualization/dervish_viz.py - Visualization of sail constellationsrc/physics/hubless_dervish.py - Sail physics + wind tacking
