A skydiver exits at 4 000 m. Before the canopy opens, the drop zone is already watching through their eyes.
Live from 4 km — 14 ms behind reality.
the actual gate-verified CAD — spin it and watch the parts fly home yourself in the 3D Lab
▶ Play the jump · 🧊 3D Lab · 🪂 Freefall Simulator · 🚧 Gate Simulator · ⚖ vs GoPro · 🎛 Antenna decks · Build it — one page · What the gates caught · The numbers · Legal (DE)
Today the ground sees a dot in the sky. Spectators, the waiting area, your own team — they follow the jump with the naked eye, and the footage arrives only after landing. The moment itself stays invisible.
SkyLive puts the jump on the screen as it happens. A helmet-mounted transmitter the size of an action cam sends a digital HDZero picture from ~4 km up, down its own 5.8 GHz radio link — no internet, ~14 ms — straight onto the big TV in the waiting area. Not a recording. The present tense.
That's the entire transmitter: a radio, a camera, a battery, and a button. The simplicity is the design — and you pick your wiring path:
- Soldered (recommended for the flight unit): every lead cut to its true run length — shorter cables, less weight, nothing to rattle, the most robust joints a jump can ask for.
- Wago quick-build (great first build): three 221-412 lever clamps, zero solder, re-openable in seconds — perfect while you're still iterating.
| part | what it does | the real part | |
|---|---|---|---|
| 📡 | Radio (VTX) | turns the picture into a 1 W digital signal, ~14 ms | HDZero Freestyle V2 (30 × 29 × 14 mm, runs directly on 3S — no flight controller, no BEC) |
| 👁 | Camera | HD skydive POV, 162° | HDZero Nano90 (ships in the VTX kit, powered over its MIPI cable) |
| 🔋 | Battery | ~40 min at 1 W (calculated: 850 mAh / ~1.3 A) | Tattu R-Line 3S 850 mAh (XT30) |
| 🔘 | Switch | on/off — breaks the battery + line directly | 12 mm latching push-button, panel-mount |
The VTX side plugs in via its stock JST-GH 6-pin harness either way. Full step-by-step (with the three hardware-killer rules): build/BUILD_GUIDE.md.
The shell: an upright, two-storey GoPro-style case — battery downstairs behind its own tab-locked door, radio + camera upstairs under a screwed roof lid — printed in PETG/ASA (never PLA) with a sacrosanct 3 mm wall, long passive louver vents, and a GoPro mount underneath. Outer dimensions: 71 × 39.5 × 56 mm — genuinely action-cam-sized. Both short sides carry an identical T-clamp strain-relief interface at the top edge — guide slot, round seat, and a screw-driven nose clamp — so the antenna can anchor left or right; the unused side is closed by the same T-piece. It builds from the parametric script in build/cad/ and passes every geometry gate on each rebuild; this exact file set is what went to the printer.
Two sizes, one architecture. Don't take a photo's word for it — spin both in the 3D Lab, where every dimension tag is a real millimetre from the executed CAD. The 850 (71 × 39.5 × 56 mm) is the flight unit; the Mini 300 (59.5 × 39.5 × 48 mm, −28 % volume) is the same design wrapped around a 300 mAh pack — same T-clamp antenna anchors (literally the same printed T-piece), same tab door, same camera corner. The width stays 39.5 on both because the radio and camera set it, not the battery.
There is no electronic antenna switch on the sender — the omni rides outside on its semi-rigid coax, and the clever part lives where it belongs: on the ground.
The mount is a proper screw clamp, measured off a working reference build's STEP files: the Ø 3.1 mm semi-rigid coax drops from above through a guide slot all the way down into a round Ø 3.2 seat that passes horizontally through the case wall — the seat has clearance, on purpose. The clamping is the T-piece's job: its stem ends in a convex nose of R 1.55 mm — exactly the cable's radius — and two vertical M2 cap screws pull that nose 0.4 mm down onto the cable, pinching it into the seat. The screws are the clamp; a yank on the antenna loads the printed wall and the bolted nose, never the connector. Outside, the RHCP omni sits directly against the wall, its axis horizontal, pointing straight through it. That 90° turn is the whole point: an upright omni's donut pattern has its nulls pointing up and down, which in head-up and head-down would aim a null exactly at the receiver. Lying sideways, the donut fires down and up and all around — signal toward the ground in every jump attitude. Both short sides carry the identical interface, so the anchor moves left or right to suit the helmet setup — one T-piece design, printed twice, no drilling, no notching.
| honest caveat | status |
|---|---|
| Body shadow, not the antenna, is the limiter in belly/sit poses (−7…−12 dB literature midpoints) | assumption, to be jumped |
| Nose clamp holding force and S11 with the coax clamped | MEASURE_ME — fit-print pull test + NanoVNA |
| CAD asserts a 0.4 mm nose-to-cable engagement (1.15 mm³) on every rebuild | calc, not a torque test |
Two earlier antenna integrations — the fully encapsulated side-capsule omni and the
down-firing patch shell — are preserved as engineering studies with their full RF derivations
in build/ENGINEERING/antenna_capsule.md; the external
anchored omni won on serviceability (swap an antenna in seconds, nothing to detune, one part to
reprint).
The gain lives on the ground. You're tumbling; the ground isn't. A bigger helmet antenna buys ~2–3 dB; aiming the ground antenna buys 10–14 dB. So the ground station is an HDZero BoxPro (4-way diversity, HDMI out to the TV) with an aimed TrueRC X²-AIR patch (nominal 13 dBic — honestly, expect ~10), a Double AXII 2 LR horizon omni and a Matchstick overhead omni. The receiver rides the best branch, frame by frame.
| value | status | |
|---|---|---|
| 📡 Transmit power | +30 dBm (1 W) — 25 mW SRD for all tests, PMSE assignment for the event | planned path |
| 📡 Free-space loss @ 4 km | 119.8 dB (5.8 GHz, Friis) | derived |
| 📡 Link margin @ 4 km | head-down ≈ +9 dB · back ≈ +3 dB · belly rides the threshold (−0.2 dB) · sit ≈ −2 dB — margins improve 2–3 dB per km of descent | calculated, not measured |
| 🧍 Body shadow | −7…−12 dB with the side-mount offset (literature midpoints) — the single biggest uncertainty | assumption, to be jumped |
| 🌡 Heat at 1 W | ~13 W of waste heat. On the ground, in still air, no passive case can hold that — so the doctrine is 25 mW on the ground, 1 W only at door-open; in freefall the 200 km/h wind is the heatsink (4–8× surplus) | calculated |
| ⏱ Latency | ~14 ms | manufacturer figure |
The full model — pattern math, pose-by-pose margin tables, every assumption and its direction of error — is in build/rf/, including an interactive link-budget explorer you can open in any browser. The thermal, structural and print derivations live in build/ENGINEERING/.
No overclaiming. A CAD boolean check is not a test. Nothing in this repo carries a measured badge yet — and when the 2026 recalculations made numbers worse, the worse numbers were published.
Everything a re-builder needs is under build/:
- 📋
BUILD_GUIDE.md— the solder-free assembly, the wiring map, the three hardware-killer rules, and the power/thermal operating doctrine. - 🛒
BOM.md— every part with real EU prices (as of 2026-07). - 📐
MEASURE.md— the dimensions you must caliper yourself (nothing in this project is guessed). - ✅
VERIFICATION.md— how a CAD model is turned into a trustworthy printable part: a seven-layer defense-in-depth, the honest limits of gates vs. physical tests, and the release checklist. - ⚖️
LEGAL_DE.md— the German regulatory situation, honestly: what is legal today (25 mW SRD), what the event path is (PMSE), and why 1 W under an amateur licence is locked pending clarification. - 🧊
cad/— the parametric build123d scripts (spec.pyis the single source of truth for every dimension).
Print released (2026-07). The concept, the electronics, the RF doctrine and the engineering derivations are done and published here; the case design is frozen and the first fit-print is in the lab.
- ✅ Sender electronics bought and specified — four parts, solder-free.
- ✅ RF doctrine derived and published (donut orientation, ground diversity, capsule study) — calculated.
- ✅ Thermal, structural and print-factor derivations published — calculated.
- ✅ Final case CAD (71 × 39.5 × 56 mm) builds watertight and passes every geometry gate — roof lid on 3 corner inserts, tab-locked battery door, twin T-slot antenna anchors, 3 mm wall. Print files released; the first fit-print is on the printer. Geometry-verified, not yet a physical test.
- ✅ Mini-300 variant (59.5 × 39.5 × 48 mm, Tattu 300 3S HV): full architecture port of the final build — same T-slot anchors (the T-pieces are literally the same printed part), same tab door, no power switch (the electronics storey has no room for one; power = plug the battery).
build/cad/mini_300.py, geometry-verified, not yet printed. - 🔜 Then: fit-print feedback → thermal measurement (multimeter protocol is written) → antenna S11 with the coax clamped → 25 mW range test → test jump.
⭐ Star the repo — releases will carry the first real measurements and, eventually, the first freefall footage from the system itself. Building one, or flying camera and have opinions? Open an issue.
4000 m ─┤ ██ EXIT link margin: head-down +9 dB · belly −0.2 dB [CALC]
3000 m ─┤ ██ freefall ~200 km/h — the airstream IS the heatsink [CALC]
1500 m ─┤ ██ canopy margins improve 2–3 dB per km of descent [CALC]
300 m ─┤ ██ pattern ground diversity rides the best of 4 antennas
0 m ─┴─▓▓─ beer footage was live the whole way down [PLAN]
The whole repo runs on a two-word doctrine: a CAD boolean is not a test. Current state of every load-bearing number:
| number | value | status |
|---|---|---|
| case dimensions, both senders | 71×39.5×56 · 59.5×39.5×48 | 🟢 executed CAD, gate-checked |
| battery | 58×30×22 (850) · 45×17.5×15.3 (Mini) | 🟢 measured with calipers |
| brass inserts | M3 Ø5×6 · M2 Ø3.2×3 | 🟢 measured |
| XT30 wire, coax jacket | Ø2.8 · Ø3.1 | 🟢 measured |
| GoPro teeth 3.0 / gap 3.3 | first fit-print in progress | 🟡 printing now |
| antenna clamp holding force | screw-driven nose, 0.4 mm engagement (calc) | 🔴 MEASURE_ME — pull test pending |
| antenna S11, insert strength, snap cycles | — | 🔴 MEASURE_ME |
| link budget @ 4 km, thermal model | full derivations in build/rf | 🟡 CALC — to be jumped |
🟢 measured · 🟡 calculated/derived and labelled · 🔴 open, honestly. When the 2026 recalculations made numbers worse, the worse numbers were published — that policy stands.
A solo-built, prototype-stage project shared in full. Calculated values are marked as such and separated from what still has to be measured. Transmit power is regulated: the plan of record is licence-free 25 mW SRD for all development tests and a PMSE short-term frequency assignment for event operation — see DISCLAIMER.md and build/LEGAL_DE.md.
License: CC-BY-4.0 · CAD: build123d (Python) · Made by @SchoenTom