7-inch autonomous quadcopter on ArduPilot: parts list and flight-time sums

We get this brief from students often: a 7-inch quad that flies GPS waypoints, sends telemetry, runs computer vision on board and stays up for 15 to 20 minutes. All of it fits on a 7-inch frame. The flight time is the hard part, and the battery decides it.

What the brief turns into

Each line of the brief maps onto hardware.

• Waypoint navigation and GPS flight need an autopilot running ArduPilot, a GNSS receiver with a compass on a mast, and a power module so the autopilot knows how much battery is left.
• Telemetry is a pair of radios between the aircraft and a laptop running Mission Planner or QGroundControl.
• Manual override is still needed. ArduPilot's failsafes are built around an RC link, and whoever is flying must be able to take the aircraft back. That means a transmitter and a receiver.
• Computer vision means a companion computer and a camera on board, talking to the autopilot over MAVLink.
• 15 to 20 minutes is a question of weight and battery, and the next two sections work it through.

Seven inches suits this brief. A 5-inch frame can't carry a companion computer for long. A 500 mm frame such as the X500 V2 carries one easily, but it is harder to transport and costs more when it crashes. If the payload grows beyond a Raspberry Pi and a small camera, use our final-year project build instead.

Start with the weight

Write the weight budget before you buy anything, because every later number depends on it. These are typical masses for this build. Weigh your parts as they arrive and correct the sheet.

The Pixhawk 6C Mini, Micro M10 and PM02 V3 figures are Holybro's. The rest vary by brand, and the wiring line is the one students most often underestimate.

Choosing the battery by doing the sums

You can estimate hover power from the propeller size and the weight alone. For one rotor, the ideal power is P = √(T³ ÷ 2ρA), where:

• T is the thrust that rotor must make, in newtons: all-up mass in kg × 9.81 ÷ 4.
• ρ is air density, 1.2 kg/m³ near sea level. It is lower on a hot day or at altitude, and the power goes up.
• A is the area swept by one propeller. A 7-inch propeller sweeps 0.0248 m².

Real propellers and motors lose a good share of that. Divide by a figure of merit of about 0.5 for a small propeller, and by about 0.78 for the motor and ESC. Then add the electronics: roughly 3 W for the autopilot, GPS and radios, and 5 to 8 W for a Raspberry Pi 5 running a vision model. Call it 10 W.

Worked example. With a 450 g Li-ion pack the aircraft weighs about 1,170 g. Each rotor must make 1.17 × 9.81 ÷ 4 = 2.86 N. The ideal power is √(2.86³ ÷ (2 × 1.2 × 0.0248)) = 19.8 W. Divided by 0.5 and 0.78 that is 50.9 W per motor, or 204 W for four, and 214 W with the electronics.

The pack is six 21700 cells at 3.6 V and 4.5 Ah: 97 Wh. Plan to use 80% of it and land with the rest, which leaves 78 Wh. The hover time is 78 ÷ 214 × 60 = about 22 minutes.

The same sum for four common packs:

The 6S LiPo most FPV pilots use gets about 13 minutes with this payload, short of the brief. The 4,000 mAh LiPo just reaches it. The single-row Li-ion pack meets it with minutes to spare, which makes it the pack to build around. The two-row pack flies longest on paper, but at 1.6 kg it pushes a 7-inch frame and its motors hard. At that point, move to a bigger airframe.

Li-ion has a catch. It holds more energy per gram than LiPo but gives less current. A single-row pack can only supply what one cell is rated for, so check the continuous rating on the cell's datasheet. Good 21700 cells are rated at 30 to 45 A, which at 22 V is several times the hover power. That is plenty for autonomous flight, but not for hard manoeuvres. Li-ion voltage also sags more under load. Set the low-battery failsafe from the voltage you log in a real hover, not from the cell's resting voltage.

Two more corrections, pulling in opposite directions. A multirotor in steady forward flight needs less power than in a hover, so a waypoint mission usually beats these numbers. Vision work tends to mean loitering over a target, though, so plan against hover. And the 0.5 and 0.78 are assumptions. After the first flights, hover for three minutes, take the average current and voltage from the log (the PM02 V3 reports both), and redo the sum with the power you measured.

Thrust and the speed controller

A camera platform that must hold position in wind needs a thrust-to-weight ratio of at least 2:1. At 1,170 g that is 2,340 g in total, or about 600 g per motor at full throttle on 6S. Look it up in the motor maker's thrust table for your exact propeller. Most 2806 to 2808 motors on 7-inch propellers clear it with room to spare.

The same table gives the full-throttle current per motor. It must stay under the ESC's continuous rating. The T-Motor F55A PROII is rated for 55 A per motor on 3S to 6S, runs AM32 firmware and bolts to the usual 30 × 30 mm stack holes. On most 7-inch combinations the full-throttle current stays well below 55 A, but check your motor's figure.

Wire the ESC's signal harness to the autopilot's FMU outputs, which can send DShot. Turn on bidirectional DShot so ArduPilot's harmonic notch filter can follow each motor's RPM. That filter does more for a clean position estimate than any other setting on this aircraft. Our ESC guide explains DShot and output groups in more detail.

The PM02 V3 sits between the battery and the ESC. Holybro rates it at 60 A continuous and 100 A for under a minute, on 2S to 12S, and it supplies 5.2 V at up to 3 A to the autopilot. This aircraft hovers at about 10 A. A full-throttle climb on all four motors can briefly pass 60 A, which is what the burst rating is for, so don't hold full throttle.

Wiring the autopilot

The Pixhawk 6C Mini has two telemetry ports and two GPS ports. This arrangement uses all four:

Both the Pixhawk and the Raspberry Pi use 3.3 V serial logic, so TX goes to RX and RX to TX with a common ground and no level shifter. Power the Pi from its own 5 V, 5 A regulator. The power module's 5 V output belongs to the autopilot, and a Pi 5 under load will pull it down.

The software on the companion computer

The Pi talks to the autopilot with pymavlink or MAVSDK, or with MAVROS if the team works in ROS 2. For vision, OpenCV and a small detection model at reduced resolution run at a few frames per second on a Raspberry Pi 5's processor. That is enough to find a target on the ground, but too slow for avoiding obstacles at speed. The Raspberry Pi AI HAT+ adds an accelerator if you need more, at the cost of weight and power.

Keep the split simple. The autopilot flies the mission in AUTO. When the Pi finds what it is looking for, it switches the autopilot to GUIDED and sends position targets, then hands back with AUTO or RTL. The failsafes stay in the autopilot, where a crashed Python script can't turn them off. Our companion computer guide covers the power arrangement and bench tests in detail.

Setting it up in ArduPilot

1. Flash ArduCopter and set the frame to Quad X.
2. Set the motor outputs to DShot, turn on bidirectional DShot, and enable the harmonic notch filter.
3. Calibrate the accelerometers, the compass (mast up, and well away from the battery leads) and the radio.
4. Set the battery monitor to analog voltage and current and enter the pack capacity. After the first flight, compare the mAh the log says you used with what the charger puts back, and correct the current scale.
5. Set the failsafes: RC loss to RTL, ground-station loss to RTL, low battery to RTL and critical battery to land. Turn on the geofence with a maximum altitude and radius.
6. Hover in Stabilize, then AltHold. Run AutoTune on a calm day.
7. Log a three-minute hover and redo the flight-time sum with the measured power.
8. Fly short AUTO missions within sight. Only then add GUIDED control from the Pi.

Before you fly in India

With a battery on board this aircraft weighs between 250 g and 2 kg, which makes it a micro drone under the Drone Rules, 2021. Rule 42 exempts research, development and testing flights by R&D entities and by educational institutions recognised by the central government from the type certificate, unique identification number and remote pilot certificate, when they fly within their own premises or in a green zone. Ask your department how it applies that exemption and keep the answer in the project file. Check the Digital Sky airspace map before any flight away from campus. Green-zone airspace extends to 400 ft (120 m) above ground.

The radios need the same care. Confirm which telemetry band and power you are allowed to use before you order, because a radio on the wrong band cannot be changed later. Our telemetry radio guide covers the choice.

Sources.

• Mass, ports and PWM pin layout of the Pixhawk 6C Mini from Holybro's technical specification and model differences page (accessed 2026-09-23)
• Mass and compass of the Micro M10 GPS from Holybro's product page (accessed 2026-09-23)
• Input range, current ratings and output of the PM02 V3 from Holybro's product page (accessed 2026-09-23)
• Current rating, cell count, firmware and mounting of the F55A PROII from the manufacturer's published specification.
• Companion computer serial settings from ArduPilot: communicating with a Raspberry Pi via MAVLink (accessed 2026-09-23)
• DShot and bidirectional DShot from ArduPilot: DShot ESCs (accessed 2026-09-23)
• The R&D exemption, drone categories and airspace zones from the Drone Rules, 2021 backgrounder published by PIB.
• Hover power from momentum theory, as set out in J. G. Leishman, Principles of Helicopter Aerodynamics. The figure of merit and motor efficiency above are our assumptions for a small propeller, not measured values.

Published 23 September 2026. Last revised 25 September 2026. Corrections to sales@vebixautomation.com.

Building this for a project?

Send us the airframe, the payload, the flight time you need and whether it is for coursework or a competition. We will check that the parts work together and send a quotation your department can raise a purchase order against. Ask for a quote.