libdrone — Off-Grid Field Production Pod

About¶

Practical guide for operating a libdrone build, repair, and charging capability independent of grid power. Covers power budget grounded in actual libdrone tool specifications, generator and LiFePO4 battery sizing, LiPo charging protocols for 6S and 4S packs, field soldering and printing workflow, and a phased BOM calibrated to Czech pricing. Inspired by frontline Ukrainian drone workshop practice (MZAK1, Nebokray) and adapted for 1–5 person civilian resilience and survey teams.

Related documents: LD-COM-001 (civilian resilience use cases), LD-REF-005 (workshop setup), LD-REF-004 (shopping list), LD-OPS-002 (DSRA — battery and safety procedures).

Foreword¶

The libdrone workshop in Telč has a grid connection. Most of the time, this is invisible — you plug in, you print, you charge, you solder. Then the grid goes away and you discover that the drone platform you have built is helpless without it.

Ukraine taught a specific lesson to anyone paying attention: small drone teams that can operate without infrastructure are disproportionately effective. The ability to charge batteries, repair a broken arm, and print a replacement part in a field environment — without grid power, without a fixed location, without a logistics chain — is the difference between a capability and a demonstration piece.

This document specifies a realistic, costed, field-deployable production pod for libdrone Pro and Core operations. It is not aspirational. Every item is either already owned by the libdrone project or is available in Czechia within 2–5 days.

Contents¶

1. Power Budget — What libdrone Actually Draws
2. Power System Design
3. Battery Charging — 6S and 4S Protocol
4. Soldering and Electronics Repair
5. 3D Printing in the Field
6. Pod Configuration and Mobility
7. Operating Cycles
8. Winter Protocol
9. Safety
10. BOM and Cost Summary

1. Power Budget — What libdrone Actually Draws¶

Before sizing any generator or battery, establish the actual loads. Generic guides use round numbers. This section uses libdrone's specific tools.

1.1 Confirmed Load Inventory¶

1.2 Realistic Simultaneous Load Scenarios¶

Scenario A — Charging only (batteries depleted after a field session): - 2× packs on HOTA D6 Pro at 2C: ~200 W - Laptop monitoring: ~40 W - Total: ~240 W

Scenario B — Charging + repair (most common field scenario): - 2× packs charging: ~200 W - SEQURE station active: ~65 W - Laptop: ~40 W - Light: ~30 W - Total: ~335 W

Scenario C — Full production (printing a replacement arm + charging): - Prusa CoreOne+ active print (post warm-up): ~250 W - HOTA D6 Pro charging 2 packs: ~200 W - Soldering station idle-warm: ~20 W - Laptop: ~40 W - Light: ~30 W - Total: ~540 W

Scenario D — Peak spike (printer bed warm-up while charger at max): - Prusa bed heating: ~750 W - HOTA D6 Pro single-port max: ~325 W - Total: ~1,075 W

Conclusion: A 2 kW generator with a 50% headroom rule covers all scenarios including Scenario D peak with margin. A 1 kW generator covers Scenarios A and B only — viable for charge/repair without printing.

1.3 LiPo Energy Accounting¶

One libdrone Pro flight: 6S 1800 mAh pack. Energy per pack: 1.8 Ah × 22.2 V = ~40 Wh. To recharge from storage voltage (22.8 V) to full (25.2 V): ~35 Wh input at 90% charger efficiency.

HOTA D6 Pro at 2C charge rate on 6S 1800 mAh: 3.6 A × 25.2 V ≈ 90 W per port. Charge time: ~35 min from storage, ~50 min from depleted (3.5V/cell).

4 packs charged sequentially on one port: ~3.5 hours at 2C. 4 packs on dual port simultaneously (2+2): ~1.75 hours at 2C.

2. Power System Design¶

2.1 Generator — Primary Source¶

Recommended: Honda EU22i or equivalent 2.2 kW inverter generator.

The inverter generator produces clean sine wave AC — necessary for the Prusa CoreOne+ and the HOTA D6 Pro, both of which contain switching power supplies sensitive to waveform quality. A conventional AVR generator at 2 kW is cheaper but produces a noisier waveform and may cause HOTA D6 Pro to fault at high charge rates. The price delta (~5,000 CZK) is worth it.

Czech-available alternatives: - Hyundai HY2000Si — 2.0 kW inverter, quieter than AVR, ~18,000 CZK - Honda EU22i — 2.2 kW inverter, ~26,000 CZK, better fuel efficiency - Einhell TC-PG 2200 — conventional (not inverter), usable for charging-only scenarios

Do not use the generator for printing and heavy charging simultaneously unless the generator is 2 kW+ inverter. Scenario D peak (1,075 W) approaches the limit of a 1 kW generator — it will trip the overload protection.

Fuel consumption: Honda EU22i at 500 W load ≈ 0.3 L/hr. At 1,000 W ≈ 0.6 L/hr. A 5 L Jerry can provides 8–16 hours of operation depending on load.

The minimum viable generator for libdrone field operations is 2 kW inverter type.

2.2 LiFePO4 Buffer Battery¶

A LiFePO4 battery bank absorbs generator output during low-draw periods and supplies peak demand spikes (e.g. printer bed heat-up) without loading the generator beyond its rating.

Recommended: 100 Ah 12.8 V LiFePO4 (e.g. Eco-Worthy, Epoch, or Jakiper)

This battery is the buffer between the generator and the loads. The generator charges it when loads are low; it supplies loads during peaks. This also allows solar panels to top up the buffer during daylight without requiring generator runtime.

Runtime on buffer alone (Scenario B, ~335 W): 1,020 Wh ÷ 335 W = ~3 hours of charge+repair work without generator.

2.3 Solar Input¶

Solar extends buffer capacity during daylight and reduces generator runtime. It does not replace the generator — a single panel cannot run the Prusa.

Recommended: 200 W foldable panel + Victron SmartSolar MPPT 100/20

The Victron MPPT is critical — a PWM controller wastes 20–30% of available solar energy in mismatched conditions. The SmartSolar also provides Bluetooth monitoring (Victron Connect app) showing state of charge and generation without an additional display.

At Czech summer sun (5 peak sun hours/day): 200 W × 5 h × 85% efficiency = ~850 Wh/day into the buffer.

At Czech winter sun (1.5–2 peak sun hours/day): 200 W × 1.5 h × 75% = ~225 Wh/day — insufficient standalone, useful as supplement.

2.4 12V DC Output and AC Inverter¶

The LiFePO4 buffer runs at 12.8 V nominal. Two distribution paths:

12V DC direct: HOTA D6 Pro has a DC input (XT60, 11–30 V). At 12V input, it delivers full 325 W. Running the charger direct from the LiFePO4 via DC is more efficient than AC→inverter→HOTA internal DC conversion (~85% efficient vs ~95% efficient DC direct). Always use DC direct for the charger when available.

AC inverter (1 kW pure sine): Required for Prusa CoreOne+, laptop, and any other AC-only equipment. A 1 kW pure sine inverter is sufficient — the printer peaks at 750 W but the buffer absorbs the spike.

⚠️ Do not use a modified sine wave inverter with the Prusa CoreOne+. The printer's power supply may run warm and the steppers may produce audible noise. Pure sine only for the printer.

3. Battery Charging — 6S and 4S Protocol¶

3.1 Equipment Already Owned¶

HOTA D6 Pro — 325 W, 15 A, 1–6S, dual AC/DC. This is the correct charger for all libdrone batteries. No additional charger is required for a 2-drone field operation. Additional chargers add complexity and split the 325 W budget across more units with no net gain for a 4-pack inventory.

3.2 Pack Inventory Recommendation¶

For 2-drone continuous operation (Pro + Core), maintain:

4 packs per platform supports continuous operations: one drone flies while the other's packs charge. Flight + recovery takes ~20 min; charging at 2C takes ~35–50 min. The rotation is not perfectly continuous but provides a natural maintenance and data-review window between sorties.

3.3 Charge Rate Guidelines¶

2C is the maximum recommended charge rate for field operations. Higher rates (3C–5C) are technically possible on 150C-rated packs but generate significant heat and accelerate cell degradation. The time saving is marginal (35 min → 20 min) and the risk is real. Use 2C.

3.4 Field Charging Protocol¶

Before charging: ☐ Let pack cool 15 minutes after flight — do not charge a warm pack ☐ Inspect visually: swelling, deformation, connector damage ☐ Check cell voltage spread: reject any pack with >0.05 V cell imbalance ☐ Set charger to balance charge mode — always, every time, no exceptions

Charging: ☐ Set charge rate to 2C for the relevant pack capacity ☐ Place pack in dedicated ammo box (item 19b from BOM) during charging ☐ Do not leave pack unattended without the ammo box — not negotiable in field conditions ☐ Set HOTA D6 Pro to alert on completion — do not estimate charge time

After charging: ☐ If not flying within 24 hours: set to storage mode (3.85 V/cell = 23.1 V for 6S) ☐ Store packs in individual ammo boxes, separated from tools and electronics ☐ Never store packs in the same physical space as fuel (generator petrol)

3.5 Field Charging Power Draw¶

Running both HOTA D6 Pro channels simultaneously: - 2× 6S 1800 mAh at 2C: 2 × (3.6 A × 25.2 V) = 2 × 90 W = 180 W - 2× 4S 850 mAh at 2C: 2 × (1.7 A × 16.8 V) = 2 × 29 W = 58 W

Total charging load (4 packs simultaneously, dual Pro packs split across channels): ~180 W — well within 325 W HOTA limit and Scenario B budget.

4. Soldering and Electronics Repair¶

4.1 Equipment Already Owned¶

Note on Omnifixo: The Omnifixo is a magnetic third-hand positioning system — not a soldering iron. It holds PCBs and wires in position during soldering. The soldering iron is the SEQURE station.

4.2 Field Repair Scenarios and Time Estimates¶

4.3 Field Soldering Setup¶

The FNIRSI SAG-55 hot air gun draws 550 W. At 12V DC from the LiFePO4 buffer via an inverter, a 60-second burst for heat-set inserts or reflowing a connection draws approximately 550 Wh/60×60 = ~9 Wh. Trivial on a 1,020 Wh buffer. Use it freely — the constraint is not power but operator safety (fumes).

Always run the NEWACALOX fume extractor during any soldering session outdoors. The outdoor airflow disperses flux fumes, but the extractor still catches the concentrated near-source plume that causes long-term respiratory damage.

Minimum viable field repair kit (what to pre-pack — not sourced in the field): - SEQURE station + tip set - Omnifixo arm set - Solder (Sn60Pb40, 0.8 mm, rosin core) - Flux pen - Kapton tape - Heat shrink (2mm, 4mm, 8mm assortment) - 18 AWG and 26 AWG silicone wire (0.5 m of each) - XT60 pair + XT30 pair - MR30 pair × 4 - GX12-7 connector pair × 2 (payload interface) - USB-C cable (Betaflight configurator connection) - FTDI adapter

5. 3D Printing in the Field¶

5.1 What Can Realistically Be Printed in the Field¶

The Prusa CoreOne+ draws ~750 W peak and ~250 W average during print. This is the largest single load in the pod. It cannot run indefinitely on battery alone — it requires the generator.

Print the things that break. Pre-print the things that might break.

Field printing rule: arm shafts and tabs only. A full frame rebuild (40–50 hours) requires the generator running for two consecutive days — not realistic in a mobile deployment. Carry 4 printed arm shafts and 4 tabs as pre-built spares. Field printing is for replacement of shafts that have crashed beyond your spare inventory.

5.2 Generator Runtime for Field Printing¶

One arm shaft print (~20 min at ~250 W average): - Generator runtime: 20 minutes - Fuel consumed: 0.3 L/hr × 0.33 hr = ~0.1 L - Cost: negligible

Printing all 4 arm shafts simultaneously (one per build plate load): - Total print time: ~80 minutes - Generator runtime: 80 minutes - Fuel: ~0.4 L

Pragmatic recommendation: run one print session per deployment day if repairs are needed. Start the generator, warm up the printer (10 min), print shafts, charge batteries in parallel (charging adds ~180 W to the load, total ~430 W — fine for the 2 kW generator), shut down when done.

5.3 Filament in Field Conditions¶

PETG is humidity-sensitive but not as acutely as PLA. For field printing (outdoor exposure up to 8 hours), a sealed bag with silica gel desiccant is sufficient protection for PETG.

Field filament kit: - 500 g PETG Natural (arm shafts, tabs) — sealed bag + 50 g silica gel - 250 g ASA Natural (bumpers) — sealed bag + 25 g silica gel - PCCF is not recommended for field printing — abrasive on nozzles and requires more careful calibration. Carry PCCF structural parts pre-printed from the workshop.

The Prusa CoreOne+ requires calibration before printing after transport. The bed levelling mesh must be redone if the printer was moved significantly. Budget 10–15 minutes for calibration before the first field print.

6. Pod Configuration and Mobility¶

6.1 The Minimal Kit (Backpack + 1 Person)¶

For solo operations or when vehicle transport is not possible:

The 20,000 mAh power bank at 65 W limits charge rate to ~0.7C on 6S packs — slower than ideal but functional for 1–2 pack refreshes between sorties. The HOTA D6 Pro accepts USB-C PD input.

This configuration supports 2–3 hours of field operations from a single backpack with no grid or generator. It is the minimum viable resilience configuration.

6.2 The Vehicle-Based Pod (1–3 Person Team)¶

Transport: any car boot or small van. The generator is the bulkiest item.

Weight breakdown:

53 kg is manageable for two people. It fits in a standard estate car boot or van shelf. The generator is the heaviest single item — carry it with two people.

6.3 Bike Cargo Trailer Configuration (1 Person, Silent)¶

For deployments where noise discipline matters or where a vehicle is not available, the LiFePO4 buffer + solar provides a silent option. The generator stays behind.

Silent pod on cargo trailer: - 100 Ah LiFePO4: ~11 kg - 200 W solar panel (folded): ~3 kg - MPPT + inverter: ~2.5 kg - Drones + batteries + repair kit: ~10 kg - Total trailer load: ~27 kg — within rating of most cargo trailers

Runtime without generator (from full LiFePO4): - Charging only (180 W): ~5.6 hours - Charging + repair (335 W): ~3 hours - Solar top-up in summer: +850 Wh/day — extends operations significantly

Printing is not possible on this configuration (no generator). Carry pre-printed arm spare set.

7. Operating Cycles¶

7.1 Single-Day Deployment Cycle¶

This assumes 2-drone operation (Pro + Core), vehicle pod, 8-hour deployment.

06:00  Depart. Generator pre-started 10 min before departure for warm-up.
       Prusa CoreOne+ printing replacement arm shafts during transit (van).
       HOTA D6 Pro on DC: charging 4× 6S packs.

07:30  Arrive at site. Generator running. Printer finishing arm print.
       LiFePO4 buffer charged to 100% by generator during transit.

08:00  First sorties begin. 2× drones airborne.
       Generator off — LiFePO4 sustains charger (Scenario A: 240 W).

09:00  Pack 1 + 2 depleted. Swap to Pack 3 + 4. Start charging 1 + 2.
       Generator on if printing or heavy repair needed.

12:00  Lunch break. All packs on storage charge (2C down to 3.85V/cell).
       Generator off. Laptop review of morning data.

13:00  Afternoon sorties resume. 4× fresh packs available.

17:00  Final sorties complete. All packs on charge.
       Generator on for 1-hour charge session + arm shaft print if needed.

18:00  Pack down. All packs at storage voltage.
       Generator off. Return transport.

7.2 Multi-Day Deployment Cycle¶

For 2–3 day deployments, the key constraint is fuel (generator) and filament (spares). A 20 L fuel can covers approximately 30–40 hours of intermittent generator use — more than sufficient for 3 days.

Daily fuel budget: 1–2 L for charging sessions + printing. Daily filament budget: 60–120 g PETG if printing replacement shafts.

Pre-deployment checklist for multi-day: ☐ Generator oil level and fresh fill ☐ LiFePO4 at 100% (charge from mains before departure) ☐ 20 L petrol in approved NATO jerry can ☐ 8× packs at storage voltage (charge to full the night before deployment) ☐ 8× printed arm shaft spares packed ☐ 500 g PETG in sealed bag ☐ Full repair consumables kit topped up

8. Winter Protocol¶

libdrone in Czech winter conditions (0°C to −15°C) requires specific adjustments.

8.1 LiPo Batteries¶

LiPo cells lose capacity non-linearly below 0°C. A 6S 1800 mAh pack at +5°C may deliver only 60–70% of rated capacity. At −5°C, expect 50%.

Winter charging: Do not charge cold packs. Let them warm to room temperature (or at minimum +10°C) before charging. A cold LiPo accepts charge poorly and the chemical process is incomplete.

Winter field procedure: - Store packs inside the vehicle or in an insulated bag until 5 minutes before flight - After landing, return packs immediately to warm storage - Set Betaflight minimum cell voltage to 3.6 V (not 3.5 V) for winter - Expect 30–40% shorter flight times — plan sorties accordingly

8.2 Generator¶

Inverter generators start harder in cold weather. Keep the generator in the vehicle during transit. Allow 3–5 minutes warm-up before connecting loads in temperatures below −5°C.

Fuel: petrol thickens slightly below −10°C. Standard 95 octane fuel is fine to −20°C. No winter additive required for Czech conditions.

8.3 3D Printing¶

PETG and PCCF are more brittle below 0°C. Do not print outdoors in freezing conditions — the cooling rate is too fast and parts will delaminate or crack.

If printing is essential in cold conditions, insulate the Prusa CoreOne+ enclosure. A simple cardboard sleeve over the printer during printing maintains a ~30°C ambient inside — sufficient for PETG.

Printed arm shafts become slightly more brittle below −5°C. The crash-sacrificial behaviour still works (they still snap on impact), but the snap point shifts — lower-energy crashes may not break the shaft, transmitting force to the tabs instead. Inspect tabs carefully after winter crashes.

9. Safety¶

9.1 LiPo — the Real Risk¶

LiFePO4 (the buffer battery) does not undergo thermal runaway. LiPo (the drone flight packs) does. The separation between these two chemistries in field setup is not optional.

Mandatory separation rules: - LiPo flight packs: always in individual ammo boxes during charging and storage - Never charge LiPo packs inside a vehicle with windows closed - Never store LiPo packs in the same enclosed space as petrol - Damaged or swollen LiPo: discharge in saltwater, do not transport inside a vehicle

Fire response: LiPo fire cannot be extinguished with water (water reacts with lithium) and is not effectively smothered. The correct response is containment — move the burning pack to an open area away from fuel and other batteries. An ABC powder extinguisher can knock down the initial flame but will not stop thermal runaway once started. Sand bucket is useful for smothering a pack that has not yet reached thermal runaway. The primary mitigation is prevention through the charging protocol above.

9.2 Generator¶

• Store petrol in approved NATO-spec steel jerry cans, not plastic containers
• Maximum on-site fuel: 20 L (legal limit in Czech Republic without special permit)
• Generator exhaust: always directed away from personnel and the drone operating area
• Never run the generator inside an enclosed space — CO poisoning
• 1.5 m minimum clearance from all equipment when running

9.3 Field Soldering¶

• Fume extractor mandatory during any soldering session
• LiPo packs disconnected and physically separated from the soldering area
• Never solder a pack that is not fully discharged to storage voltage or lower

10. BOM and Cost Summary¶

10.1 What Is Already Owned¶

The following items from the libdrone project require no purchase:

10.2 Phase 1 — Charging Independence (~12,000 CZK)¶

Enables off-grid charging without printing. Backpack or vehicle deployable.

Phase 1 uses vehicle engine or mains to charge the LiFePO4, then provides autonomous charging and repair capability for 3–5 hours without any generator.

10.3 Phase 2 — Generator + Solar (~24,000–32,000 CZK)¶

Adds printing capability and extended runtime.

10.4 Phase 3 — Mobility Hardware (~5,000–8,000 CZK)¶

Packaging for mobile operations.

10.5 Total Cost Summary¶

Existing equipment (already owned) would cost approximately 45,000–55,000 CZK to replace — this is not an additional cost but the sunk investment the pod is built around.

Phase 1 alone (12,000 CZK) is the most impactful first step. It converts the existing workshop into a deployment-capable field kit without the generator.

Revision History¶