I'm trying to build a system that would allow me to monitor a moving object in real time, to estimate its average speed over a fixed distance. The issue is that the object is a drone, it can't be guaranteed to cross a specific horizontal or vertical line, so using a lidar, or an ultrasonic sensor didn't seem like a good way to go. The other concern is the accuracy, latency/delay in timing between start and finish, even in milliseconds isn't acceptable.

The system I'm trying to build consists of three components, a start line, a finish line and a tag/ some type of transmitter.

The starting line and finish line are two identical devices that would detect when the tag crosses them, so when the drone starts and finishes the journey, but my application requires being able to detect the drone even if it was to be high from the ground, say 10-15 meters. I tried researching suitable sensors but had no luck figuring out what suits my needs. model

Any suggestion for the hardware would be greatly appreciated

  • 2
    This isn't really an IoT question...
    – romkey
    Jul 20, 2022 at 23:55
  • A quite different approach, but have you considered a Doppler radar? What’s the width of the “gates” and the size of the drone?
    – jcaron
    Jul 21, 2022 at 14:44
  • The drones are tiny, and the "gates" is a half circle with a 10meter radius, or something near that. I don't think the doppler radar would work accurately in that scenario, but i'll look into it.
    – Rami
    Jul 27, 2022 at 5:55
  • What's "tiny"? The most accurate detection would be using a series of "break-beam" sensors across the width of the "gate". If the drones are 30 cm wide for instance (smallest dimension), then one sensor every 30 cm will be required, which for a 10m-wide gate means over 30 sensors (I suppose the drones are wider than they are high, otherwise it would make more sense placing the beams horizontally). Break-beam sensors are cheap, here's an example that's supposed to work over those distances: aliexpress.com/item/4000154782526.html but even that has a 2.5 ms response time.
    – jcaron
    Aug 28, 2022 at 13:11

2 Answers 2


Here's an alternative solution to what you're shown.
Create a way of having a bright point light from the drone.
Have a way where you take two pictures that captures this point of light from the drone.
If you can have both pictures come into the same photo frame and you know the time interval between them and are good with trigonometry...
If you cant predictably go perpendicular to the camera's line of sight, you may need two cameras synced and orthogonal. And even more trig !
Other constraints:

  • You'll have to keep the time interval short enough that the path of travel can be assumed to be a straight line.
  • You maybe only able to do this at night. :-)
  • You'll need a lot of luck! Wish you all the best.
  • Or you can just do a long exposure from the camera but have the drone flash a light at a known interval. Maybe this is easier to do. Will definitely need a dark night for long exposures ! Jul 28, 2022 at 17:16

How about using GPS coordinate information along with barometric sensing to measure altitude changes?

You can calculate speed using the SQRT ((Xnow - Xprevious)^2 + (Ynow - Yprevious)^2 + (Znow - Zprevious)^2)/(Tnow - Tprevious)

where (Xnow - Xprevious) and (Ynow - Yprevious) represent the changes in latitude and longitude between successive samples and then converted to units of meters by multiplying the.

(Znow - Zprevious) is a difference in barometric pressure converted to a change in altitude in units of meters.

and (Tnow - Tprevious) is the time in units of Seconds between successive samples

  • I doubt this would yield anywhere near the accuracy OP wants.
    – jcaron
    Nov 27, 2022 at 9:17

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