L1 Charging Pod: L1 Aircraft Results

Bottom line. The pod can charge both L1 aircraft safely at 9 A, which needs a new drone-type setting: the existing 10 A and 20 A settings must not be used on the L1 pack. With the pod kit fitted, the L1-Q's leg falls from 8.9 km to 7.2 km and the L1-W's from 36.3 km to 29.5 km in still air. Neither aircraft can use a pod as listed today: both lack the per-cell BMS and charge FET the pod requires, the listed landing camera fails the landing requirement, and L1 flight software v2.2.1 has no pod support. None of the L1 aircraft or pod software exists in built form; every figure below is simulated.

Data used. L1 values come from the L1 design reference and parts lists (v2.2.1). These are engineering estimates for aircraft that have not been built or flown. Both aircraft carry a 6S2P pack of Molicel P45B cells (about 194 Wh, 900 g). From the cell data sheet: 4.5 Ah typical per cell (4.35 Ah minimum), standard charge 4.5 A, maximum continuous charge 9 A (with faster capacity loss), charge temperature 0–60 °C, AC impedance at most 8 mΩ per cell. The pack is therefore 9.0 Ah: 1C is 9 A and the maker's maximum is 18 A. The model takes the pack's ohmic resistance as 42 mΩ (an assumption: 1.5 times the AC figure plus wiring and BMS) plus 12 mΩ of polarization resistance, so at steady current the pack dissipates I² × 54 mΩ. Gaps in the L1 data (frame size, panel strings, avionics draw, battery location) are filled with stated assumptions in podsim/l1.py.

Pod charge current for the L1

The drone-type switch carries a third position, "L1: 9 A", used for both L1 aircraft (see Drone charger). Charging ends at 4.10 V per cell (about 92% charge), above the L1's 85% relaunch rule. Firmware overcurrent scales with the setting (1.25 × 9 A = 11.25 A); the 30 A hardware trip is unchanged.

Pod results with the L1 pack

• Protection. Every protection case passes on the L1 pack: converter runaway cut by hardware alone within 0.33 ms at every state of charge and both ends of the OV band; all six protection-hardware failures (worst 113.5 ms, at most 125 A, under 10 mAh added); pad short; lift-off; current and voltage sensor failures.
• Pod thermal. Unchanged: full rate to 34 °C ambient. The interior heat that sets the envelope comes from parts off the heat-sink plate, which do not depend on drone current.
• Charges per pod per day (arriving at 30%, storage reserve kept): large solar kit 10.7 on a clear 4-peak-sun-hour day and 3.8 in winter sun (1.5 hours); small kit 3.3 and 1.1; grid only, or solar plus grid, 22.5 (limited by charge time).

L1 range and pod spacing

The added mass is the 0.30 kg pod kit plus about 0.05 kg for the per-cell BMS the L1 lacks. A leg uses the L1's 107 Wh (85% to 30%). It allows 45 s of hover (L1-Q) or 30 s of extra vertical flight (L1-W) to centre on the pad. Power scales with mass to the 1.5 power for the quad and its vertical flight, and in proportion to mass in cruise. Design spacing keeps 10% for routing. Both aircraft are timed on one basis: transit (forward flight, which sets the distance) and time in the air (transit plus hover or vertical flight).

Space pods for the worst headwind expected on the route. The L1-Q's short leg makes a pod network for it dense: about one pod every 4 km in a 5 m/s headwind.

L1 on-board solar

The study simulated both panels with the Genasun charger's efficiency and night drain. It applied this design's charging rules as if the external output switch listed under gaps were fitted. Each aircraft was run with the pack directly under the panel and with the vented gap.

The clear-day figures are an upper bound. The L1 documents' own real-world averages (about 78 Wh a day for the L1-Q and 198 Wh for the L1-W) are lower. On an average day the L1-W still refills, while the L1-Q gains roughly 40% of its pack. The mounting rule holds for both aircraft: directly under the panel, the pack passes the 60 °C storage limit on a 45 °C day. Without a heater, both aircraft gain little on cold days, and nothing below about 2 °C.

L1 gaps against the pod requirements

Charger. The Genasun GVB-8-Li has no enable input, no battery temperature input on lithium models, no published latched overvoltage protection, and draws about 6 mA at night (about 3.5 Wh a day). The on-board charging rules need an added output switch driven by the BMS charge-allow signal, a 100 ms pod-current interlock, both NTCs and a latched 25.05 V comparator. Because it is a boost charger, the panel strings need Vmp below about 19.8 V at −10 °C and Voc below 24 V at −30 °C. The L1 documents do not give the strings, so this is unverified. The L1's own rule (no charging below 0 °C or above 45 °C) is wider than this design's: solar charging starts only at 5–40 °C and runs at 2–44 °C, and the pack is presented to the pod only at 10–35 °C.

In-flight solar. With the required charge FET open in flight, the panel can no longer feed the pack in flight. To keep the L1-W's in-flight gain, add the gated, load-limited output onto the discharge bus described under on-board solar charging.

Software that would have to be written (none exists in L1 v2.2.1):

1. AprilTag pad detection on the companion computer and MAVLink LANDING_TARGET output to the flight controller, with a fallback when no tag is seen.
2. Pod approach and landing: route to the pod coordinates, descent onto the pad and touchdown confirmation.
3. Charge-FET control: open before arming and in flight; close on the pad only when both pack sensors read 10–35 °C; open if either falls below 10 °C.
4. Sleep on the pod at no more than 0.3 A; wake on charge completion (pack voltage at taper) or on schedule.
5. Relaunch logic: leave at 85% or more, or at taper end, within the launch window, after re-arming checks.
6. Solar handling: the hardware interlock does the switching; firmware logs it and keeps the solar output off in flight unless the bus output is fitted.
7. Pod-occupied and pod-dead fallback: wait, divert to the next pod, or land and charge on solar.

What must change before an L1 uses a pod.

• On the pod: add the 9 A setting.
• On each aircraft:
  • fit the BMS, charge FET and balancer;
  • fit a camera to the specification;
  • add the vented gap where the battery sits under a panel;
  • add the charger output switch and interlock;
  • confirm the contact plate fits, or build a 200 mm-grid L1 pad;
  • write and flight-test the software above;
  • recompute pod spacing with measured weights and power.