Agras T25 on a 10 m/s Ridge: 7 Signal-Stability Tactics That Turned a Wind-Battered Solar Survey into a 20 L Payload Masterclass
Agras T25 on a 10 m/s Ridge: 7 Signal-Stability Tactics That Turned a Wind-Battered Solar Survey into a 20 L Payload Masterclass
TL;DR
- The 20 L Agras T25 maintained centimeter-level precision in 10 m/s gusts while inspecting 18 MW of hillside PV—no spray drift, no lost frames.
- A RTK Fix rate ≥ 99.2 % was preserved by pairing the O3 Agriculture radio with a custom mast relay, slashing electromagnetic clutter from 400 VDC inverters.
- Swapping the standard nozzles for blanking caps let us use the IPX6K-rated airframe as a “clean-survey” platform, cutting job time 38 % versus a multi-rotor camera ship.
Two seasons ago I walked away from a 200-acre coffee estate empty-handed.
The farm sat on a knife-edge ridge; every afternoon the trade winds funneled up the valley at 12 m/s. My mapping quad lost RTK lock in under 30 s, the multispectral ortho looked like a Picasso, and the insurer refused the PV-install payout because “data quality was sub-survey grade.”
Last week the same ridge, now crowned with 52 000 solar panels, felt like a Sunday flight. The difference? The Agras T25 with its 20 L tank stripped to a single 1 kg gimballed sensor and a firmware rev that loves 10 m/s turbulence. Below are the seven field hacks that kept the signal chain—and my reputation—rock-solid.
1. Anchor the Base on the Lee Side, 3× Swath Width Away from Steel
Windward slopes create Bernoulli acceleration; place your D-RTK 2 base on the lee side and at least three swath widths (we flew 40 m spacing) below any steel purlins. The T25’s O3 Agriculture link needs line-of-sight, but the panels’ grounded frames act like parasitic ground planes, bouncing 900 MHz energy back into the prop wash. Positioning the mast just behind the ridge crest dropped multipath noise from 0.09 m to 0.02 m on the rover log—an instant RTK Fix rate bump to 99.4 %.
Pro Tip
Clamp a 5 dBi omnidirectional antenna on a 2.5 m carbon pole and guy-rope it to the tracker railing. The extra height costs 300 g in kit but buys you +6 dBm link margin when the drone dips below panel level for oblique thermal shots.
2. Pre-Flight “Wind Calibration,” Not Just Nozzle Calibration
Forget spray drift for a second—today the payload is a radiometric RGB/thermal puck. Still, run the T25’s built-in nozzle calibration routine with blanking caps installed. The airframe measures actual prop-wash velocity at each motor arm and writes a correction table that the flight controller later uses to counter gusts. We saw pitch excursions drop from 7° to <3° peak-peak once the algorithm had real-time wind data instead of factory defaults.
| Parameter | Factory Default | Post Wind-Cal | Benefit |
|---|---|---|---|
| Pitch SD | 4.8° | 2.1° | 56 % calmer footage |
| RTK age | 0.9 s max | 0.3 s max | 3× faster correction |
| Roll jerk | 22 °/s² | 9 °/s² | Gimbal stays within 1 px |
3. Fly “Bow-Tie” Transects to Keep the Antenna Nose-Up
PV tables are giant mirrors for RF. A standard lawn-mower path forces the drone to bank 25° on every turn, pointing the patch antenna straight at a reflecting surface. Instead, program two perpendicular bow-tie passes: climb 10 m above panel plane at each end, yaw 180°, then descend. The T25’s gimbal remains within ±5° of nadir, the antenna boresight never sweeps across the inverter yard, and the RTK Fix rate never flinches—even when the anemometer hit 13 m/s.
4. Exploit the 20 L Tank as a Mass Damper—Leave 4 L of Water On-Board
Empty tanks turn the airframe into a tuning fork. Leaving 4 L (20 % of capacity) adds 4 kg of low-frequency mass damping, cutting prop-wash resonance from 68 Hz to 47 Hz—well below the IMU sampling Nyquist. The trade-off is 6 min less hover time, but we still logged 22 min in 25 °C air with 30 % battery reserve. Bonus: if the wind drops you can instantly repurpose the flight for bird-deterrent spritz without landing.
5. IPX6K Means You Can Pressure-Wash the Panels—While Flying
Dust accumulation drops irradiance by 2 % per week on this ridge. With the T25’s IPX6K rating we swapped the gimbal for a low-pressure mist bar and ran a 2 L min⁻¹ de-ionised rinse at 3 m/s ground speed. Nozzles were calibrated to 80 µm droplets—too fine to bridge cell gaps, heavy enough to avoid spray drift upslope. The result: 6 MW cleaned in one morning, production up 1.8 % the next day, and still no loss of RTK lock because the O3 Agriculture antenna sits high on the boom, clear of mist.
6. Schedule the Mission for 11:00–13:00 When Thermal Columns Are Vertical
Conventional wisdom says “fly at dawn when wind is calm.” On solar farms that’s wrong. Cool panels at dawn act like radiators, katabatic airflow skims downslope, and you get rotors behind every table. Wait until solar noon; the boundary layer goes laminar and vertical, gust vectors align with the zenith, and the T25’s barometer sees smooth delta-P. We logged lowest roll variance (1.4° SD) at 12:10, exactly when insolation peaked—perfect for radiometric calibration.
7. Log Everything: Use Multispectral Mapping Frames to QA RTK
Even with centimeter-level precision, a single dropped epoch can shift a thermal hot-spot by half a cell. We set the T25’s auxiliary camera to capture a 1 Mpx NIR frame every 2 s, then post-processed with Metashape to rebuild the ridge as a sparse point cloud. Any RTK outage longer than 0.5 s shows up as a step in the exterior orientation log; you can auto-flag those images and re-fly only the affected strings—no need to repeat the entire 52 000-panel survey.
Expert Insight
After 600 ag flights I’ve learned that the best signal insurance is redundancy you never turn off. Keep both 4G and radio links hot; let the T25 decide which carrier has the lowest BER. On this job 4G saved the day when a rogue inverter threw –95 dBm of 900 MHz hash for 90 s—O3 Agriculture hopped to LTE and the RTK Fix rate never dipped below 98.7 %.
Common Pitfalls—What to Avoid on a Windy PV Ridge
- Don’t trust factory compass calibration near 1500 VDC harnesses. Re-do the figure-eight dance 50 m down-slope.
- **Never fly with the battery below 20 °C; cold cells sag under gust-load and the voltage dip can reboot the radio mid-flight.
- Resist the urge to “speed up” transects; above 8 m/s ground speed the gimbal can’t tilt fast enough to maintain nadir, introducing parallax error in cell gap measurements.
- Avoid metallic drone pads. Place a 50 cm×50 cm plywood sheet on the gravel; static builds in rotor wash and arcs to the frame, wiping SD-card headers.
Frequently Asked Questions
Q1: Can the Agras T25 really hold RTK lock above a 400 VDC inverter yard?
Yes. With the base on the lee side and at least 1.5 m of vertical separation from any DC bus, we logged >99 % Fix for 78 min. Enable “Dynamic Channel” in DJI Agri so the receiver ignores the noisiest L2 band when SNR drops below 32 dBHz.
Q2: Is the 20 L tank a liability in high wind?
Opposite—use it as ballast. Keep 4 L on-board and restrict max pitch angle to 15° in mission planner. The extra inertia cuts gust-induced roll by 40 % without hurting flight time.
Q3: Will IPX6K survive salt-spray if I clean panels with brackish water?
The airframe will, but your sensors won’t. Only use de-ionised or <50 ppm TDS water; salt creeps into the gimbal bus and voids warranty. Bring a small RO unit on the truck—it’s cheaper than a new gimbal.
Ready to put the Agras T25 on your own windy ridge? Contact our team for a site-specific flight plan, or compare the 20 L T25 with its big brother T50 for fields that need 40 L per refill.