title_body: Seeking a cheap, programmable drone, for use in the UK This meta question states that recommendation questions are on-topic. However, as I am new here, I don't want to commit a fox's foot (faux pas ;-), so please vote to close, rather than downvote, if I have posted wrongly (or, just ask me to delete the question). Thanks.
  As soon as I get a single answer here, I will delete as duplicate my as yet unanswered Hardware Recommendations question Cheap programmable drone, for use in the UK, which reads:
  
  I am looking for a cheap, programmable drone, for use in UK, to use in
  a Minimal Viable Product for a system that will later use more highly
  spec’ed drones.
  • Needs to accept a programmed flight plan (*)
  • Needs to carry an
  ESP32 (approx. 10g) and a coin cell battery (2.9g), possibly an
  altimeter of GPS sensor (I would guess 5g, max 10g)
  • Long flight time is not important, but I would like 5, preferably 10 minutes
  • Outdoor use, not indoor, although I can live with being restricted
  to calm days
  (*) I am not sure if UK law requires a human drone operator, rather
  than a programmed flight plan. If that’s the law, I will comply, but I
  have a strong preference for programming a series of waypoints.
  
  [Update] do I need to be licensed to fly a drone in the UK?
  
  I hope that this question is specific enough to be acceptable. Basically, I am looking for a quick &amp; dirty demo (don't want to spend £ hundreds, in case no one bites at the idea), to demonstrate how a drone with an ESP32, or similar, can be automated to fly over sensors and collect data via Bluetooth Low Energy (BLE).
upvoted_answer: The sort of sensors and equipment you are talking about would fit on a 250mm frame (measured diagonally, between motor centres), which is the 'standard' outdoor FPV size that takes 5&quot; props. Below this size, things don't really get any cheaper but it gets a lot harder to squeeze everything into the frame.
  If you need more space, the F450 'Flame wheel' frame is pretty standard for development drones. It's heavy and fragile compared to an 250 frame though, and everything is more expensive, so I'd stay small if you can.
  'Programmable' is difficult to define as almost no one writes their own code, yet the dividing line between 'toy' and 'hobby' grade is when the flight controller has a USB port and can be flashed with (usually) open-source firmware such as BetaFlight, and the PIDs and flight modes configured.
  Most flight controllers only have a couple of inputs, one of which is used for the RC receiver. The other is for people who want to add a GPS (and some flight controllers have built in barometer and compass). In theory then, you could do everything with a standard flight controller, if you can work out how to modify BetaFlight, and you're careful to leave it enough CPU time to fly the drone.
  Alternately you could handle navigation on the ESP32 and just send the flight controller commands as if it was the RC receiver.
  The next step up are the flight controllers designed for autonomous flight, such as the Pixhawk. They have a lot more inputs and software for setting up waypoint missions. They are more expensive though.
  You probably don't need the button cell, most people use a PDB (power distribution board) to split the battery wires to the motors, and they usually also contain a 12v and 5v regulator, and often the flight controller also provides 3.3v
  Finally, you're unlikely to stay under 250g so you need to register as a drone operator with the CAA. It's only £9 and you can take the multi-choice test as many times as necessary. The rules are pretty simple (don't fly near things you wouldn't want to hit!) but you should read them to make sure you don't accidently break the law. You should also consider buying some insurance, it's pretty cheap from FPVUK or the BMFA.