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felixge / node-ar-drone

A node.js client for controlling Parrot AR Drone 2.0 quad-copters.
http://nodecopter.com/
MIT License
1.76k stars 428 forks source link

Move specific distance #116

Closed ktlmoore closed 9 years ago

ktlmoore commented 9 years ago

Hi,

This may be a stupid question but I can't quite find the answer - how would you suggest going about using ardrone to move the drone a specific amount in a windless environment (say, 1m forward)? I assume it would be: front(speed) and then stop after a certain time, but I don't see an easy way to determine what that certain time is without knowing the actual speed of the drone, which is not provided.

felixge commented 9 years ago

This is a hard problem. The drone does not know it's actual position in space, and dead reckoning (what you described) will always have a large amount of error. Your best bet is utilizing the cameras on the drone, but this in itself a challenging task, and I'm not aware of anybody in the nodecopter community having implemented such a system successfully.

sentientcucumber commented 9 years ago

There is the ardrone-autonomy module. You can provide distances to move in a given direction according to the API. I haven't used it, so I can't speak to how accurate it is, but hopefully it's helpful.

felixge commented 9 years ago

@shellhead ah, right. Completely forgot to mention that. AFAIK it uses dead reckoning, but it's doing that as good as possible :)

wiseman commented 9 years ago

General strategy

You need to

  1. Start monitoring navdata and establish your termination condition; something like "distance traveled is >= 2000 mm"
  2. Start the drone moving.
  3. Watch incoming navdata, checking whether your termination condition has been met.
  4. Stop the drone when your termination condition has been met.

Without GPS

Even without GPS, the AR.Drone can make a pretty good guess of its relative position if you're talking about smallish distances (a few meters?). An AR.Drone engineer described the navdata.demo.drone.camera.translation data as "This position is estimated using all on-board sensors and should be a bit more accurate than integrating the speed information". I believe they use optical flow from the downward facing camera combined with accelerometer data to come up with a combined best guess position. This is the data I used to implement commands like "go forward six feet" in this demo.

My ar-drone-rest library (sorry @andrew, I hadn't seen yours) uses this to offer the following sort of API:

Tell the vehicle to move forward slowly and stop when it has traveled 1 meter:

$ curl 'http://127.0.0.1/v1/stopAfter/1000'
$ curl 'http://127.0.0.1/v1/front/0.1'

You can find the implemention around https://github.com/wiseman/ar-drone-rest/blob/master/lib/server.js#L37

With GPS

If you have the AR.Drone Flight Recorder or other GPS, you can measure long distances, though maybe not as precisely. You would use navdata.gps.latFuse and navdata.gps.lonFuse to get the coordinates of the drone, and something like geolib to compute the distance between coordinates.

wiseman commented 9 years ago

Please re-open if you have more questions on this topic.