GPS drones
A GPS drone is a drone carrying a satellite navigation receiver, so that the aircraft knows its own position on the ground to within a few metres and can use that knowledge to do three things: hold a spot in the air with nobody touching the sticks, fly back to where it took off from, and refuse to drift when the air moves. Everything sold as a feature on this class comes out of those three. The receiver does not make the aircraft safe, does not make it fly itself, and does one thing badly enough to matter, which is that it stops working exactly where a beginner most wants it to.
Where this class sits
Typical take-off weights for this class, on the same scale used on every class page, so the twelve can be read against one another. The only figure here with legal force is the 250 gram line.
What a GPS drone actually is
A GPS drone is an ordinary multirotor with a satellite receiver and an aerial added, feeding a position into the flight controller alongside the gyroscope, accelerometer, barometer and compass it already has. The name is loose. GPS is one system, run by the United States, and almost every current receiver also listens to at least one of GLONASS, Galileo and BeiDou, so the accurate term is GNSS and the label on the box is a generic. A receiver needs signals from a minimum of four satellites to fix a position in three dimensions, and flight controllers usually wait for a good deal more than that, plus a period of stability, before they will let the aircraft into a satellite assisted mode.
What the fix changes is what happens when you let go of the sticks. Without it, releasing the controls levels the aircraft and leaves it drifting with whatever the air is doing. With it, the aircraft plants itself. That difference is the reason the feature became standard on camera machines, and it is discussed from the camera's side on Camera drones. What a drone actually is covers the definition of the word.
What separates a GPS drone from the rest
What separates a GPS drone from the rest is position hold, and it is a genuine engineering line rather than a marketing one. An aircraft without it flies in attitude mode: the sticks command a lean angle, the aircraft holds that angle, and the wind carries it wherever it likes, so the pilot corrects continuously. An aircraft with a fix flies in position mode: the sticks command a velocity, and when they are released the flight controller works out how far the aircraft has been pushed off the spot and flies it back. In still air the machine appears to be nailed in place. In a breeze it leans into the wind and stays where it was put.
Three further behaviours are built on the same fix, and they are the ones the class is really bought for.
- Return to home: the aircraft records a home point at launch, climbs to a set altitude on command or on low battery, flies a straight line back, and descends.
- Waypoint and orbit flight: a route or a circle is set in software and flown to the positions rather than by hand.
- Geo awareness: the aircraft compares its own position against stored airspace and restriction data and warns or limits accordingly.
The physical limit of all of it is signal quality. A satellite fix needs an open view of the sky, so it degrades under a tree canopy, in a narrow street, against the side of a building, and indoors it is gone. A partial or reflected fix is the dangerous case, because the aircraft acts on a position it believes and that position is wrong.
What a GPS drone costs
Satellite positioning used to be the line between a toy and an aircraft, and prices still carry the memory of that. Under one hundred pounds a receiver may be fitted but should be assumed to be slow to lock, poor at holding and unreliable in return to home, and at that band the more useful feature is often optical flow, which holds position by watching the ground and works indoors where satellites do not. From roughly two hundred to six hundred pounds the receiver is dependable, the return to home works, the return altitude can be set, and the aircraft reports its satellite count on screen. Above that band the money buys the camera, the obstacle sensors and the link, not better positioning: the fix does not get meaningfully more accurate for a hobby flyer, because the limiting factor is the sky rather than the receiver.
Paying more therefore stops changing the positioning almost immediately. What it does change is what happens when positioning fails, since the expensive machines fall back more gracefully and tell you more clearly that something is wrong.
What to check before buying a GPS drone
- Read which constellations the receiver uses, and prefer a machine listing more than one.
- Check whether the aircraft displays its satellite count and fix quality in flight, rather than just a green tick.
- Check whether the return altitude is adjustable, and where it is set by default.
- Find out what the aircraft does when the control link drops: hover, land, or return.
- Find out what it does when the satellite fix drops mid flight, and whether it warns before switching mode.
- Check whether it also carries optical flow for holding position low down and indoors.
- Check whether compass calibration is required before each flight and how it is performed.
- Check the weight against 250 g, since the sub 250 g machines fitted with receivers give up wind resistance to get there.
- Check whether altitude and distance limits can be set in the software before the first flight.
What flying a GPS drone is like
The first ten minutes are spent waiting, and then being surprised at how still the aircraft is. The receiver takes a minute or two to lock from cold, the controller counts satellites up, the home point sets, and only then does the machine become the thing in the advertisement: it climbs, you release the sticks, and it simply stops, in the air, at that spot. For anyone whose only previous flying was a toy, that stillness is the whole experience of the class, and it is also the source of the one bad habit it teaches, which is trusting it.
What it punishes is flying somewhere the sky is not open. Take the same aircraft between two buildings or under trees and it loses satellites, drops out of position mode without ceremony, and starts drifting exactly like the toy did, usually at the moment attention is on the screen rather than the aircraft. It also punishes a lazy compass. A compass calibrated next to a car, on a manhole cover, or beside a steel framed building will be wrong, and the classic symptom is the aircraft circling wider and wider around the point it is trying to hold instead of sitting on it. The fix is to land, move well away from metal, and calibrate again.
Caution
Return to home flies a straight line at whatever altitude has been set, and it does not know about the tree, the pylon or the crane between the aircraft and the home point. Set that altitude above everything in the area before launching, not after. Take manual control the moment the aircraft is heading somewhere wrong: return to home is a convenience, not a rescue, and an aircraft returning with a bad fix will fly to the wrong place with complete confidence.
The UK rules that apply to GPS drones
GPS drones are placed in the scheme by weight against the 250 g boundary and by whether a camera is carried, and a satellite receiver changes neither, though the geo awareness it enables can warn about restricted airspace it would otherwise be easy to enter unknowingly. The 400 foot ceiling, about 120 metres, and the requirement to keep the machine in unaided sight apply to a satellite equipped aircraft precisely as they do to any other, and an accurate position readout is not a substitute for either. The Civil Aviation Authority publishes these requirements and amends them from time to time, so they should be read there rather than taken from software built into an aircraft.
GPS drones against the alternatives
Three sibling classes are the better answer in situations this one handles badly. Indoors, a satellite receiver is useless and often refuses to engage at all, so a small optical flow machine, the class covered by indoor drones, is the better buy for anybody who wants to fly in a room. For learning to fly rather than to position, FPV and racing drones is the better class and the reason is instructive: most of those machines carry no satellite hold at all, deliberately, because the aircraft is meant to go exactly where it is pointed and the pilot is meant to be the stabilisation. And as a first present for a child, a toy machine with no receiver is more suitable, since a satellite hold on a light aircraft encourages flying further away than the child can see.
The sub 250 g satellite machine, and what it gives up
The most searched combination in this class is a camera aircraft with a satellite receiver that still comes in under 250 g, and it exists in numbers now because that boundary is the one buyers care about most. The engineering is a real compromise rather than a free lunch. Getting a receiver, a gimbal, a camera and a usable battery under the boundary means a small airframe with small propellers, and a small light airframe has less authority in wind, so the same gust that a heavier machine leans into will push a sub 250 g aircraft off station even with a perfect fix. The receiver knows the aircraft has been displaced and commands a correction; the aircraft simply cannot produce enough thrust sideways to obey quickly.
What that means in practice is a machine that behaves impeccably on a calm morning and works noticeably harder on an exposed hillside, with shorter flights because it spends battery fighting rather than flying. It is still the right choice for a great many people, because the weight class carries real advantages and the positioning works. It is worth buying with the trade understood rather than as a machine that has been given something for nothing: the fix is the same, the ability to act on it is not.
Is a GPS drone the right buy for you?
Yes, for almost anybody buying an aircraft to fly outdoors with a camera on it. The class suits somebody who wants to concentrate on the shot rather than on holding station, somebody flying in open country where a lost link matters, and somebody who would rather the aircraft came back than went for a walk. It is the wrong buy for a reader who mainly wants to fly indoors, where the receiver contributes nothing, and for a reader who intends to learn stick skills, because a position hold quietly does the flying and the skill never arrives. It is also the wrong buy for anyone who reads return to home as a guarantee, since the feature is a straight line flown by a machine that cannot see.