Wednesday, May 11, 2011

Idea: ArduPilot Differential GPS


Fail... lots of people have thought of this idea and it won't work.

Executive Summary
  • Hook a GPS to GCS.
  • GCS calculates GPS difference.
  • GCS transmits GPS correction over xbee MAVLINK connection
  • ArduCopter Stabilize mode gets very fine resolution.


I was just reading the ArduCopter 2.0 docs and saw this:

The quad should stay in a 4-5 meter diameter "circle" around the target position.

I recalled an old TV show where somebody used differential GPS (hereafter DGPS... is that a common name?) to track glacier movement... they had DGPS receivers planted across the ice, and a DGPS transmitter attached to rock.  I recall being impressed that they were able to get 1-inch resolution.

I googled around for DGPS products -- wouldn't it be neat if you could just buy something and have your ArduCopter hover with that kind of resolution! -- but found out a couple of things:

  • DGPS seems pretty common in the GIS world.
  • the definiton of "highly affordable" DGPS systems was about $15k.  Yikes!
  • "portable" DPGS receivers were touted as being easy to carry around by a single person.
  • DGPS seems to work by sending the sideband correctional signal over some kind of modem.
  • "normal" GPS receivers won't benefit from a DGPS transmitter.


So, I had an idea for implementing DGPS in the ArduPilot/ArduCopter world.
  • Hook up a GPS unit to your ground control station (GCS).  This could be any GPS unit... You could use a hand-held receiver with USB, make a custom arduino-based unit, etc.  The purpose of this unit is to be near the GCS and feed a love GPS signal of the GCS's current position.
  • When setting up the GCS, allow an absolute current position to be entered.
  • Add a MAVLINK message outbound from the GCS to the plane(s), broadcasting the difference in measured and specified absolute position and altitude.
  • When in stable mode, the ArduPilot software takes the DGPS correction into account if it is available.
  • Super Precision Stable Mode!


  1. Its not called DGPS. DGPS is standard gps technology. I think the industry term for what you are describing is RTK GPS (Real Time Kinematics). I operate gps guided agriculture equipment every day and DGPS is the standard system, accurate to 1 foot or so. RTK is accurate to sub-inch detail and requires a geo-location-known base station and ratio modems to send correction signals to the mobile station. DGPS does not. But ya, that is a sweet idea.

    Here is an link on DIYdrones that has a few insights


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