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3D RoboticsPermalink Reply by Chris Anderson on April 12, 2009 at 7:41am

That's a cool idea. You can easily get continuous rotation servos (used in robotics). Assuming the ground station and launch point are about the same, the airborn ArduPilot could send the tracking ArduPilot its home position as part of a setup string.

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Permalink Reply by Nick Sargeant on April 12, 2009 at 11:17am

Please correct me if i'm wrong but I believe continuous rotation servos have no ability to go to a fixed point (they be stationary or can rotate clockwise/anticlockwise only)?
However you could probably use external gearing on a standard hobby servo or perhaps use a special 360* rotation servo usually used for sailing boats such as the GWS S125 1T

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3D RoboticsPermalink Reply by Chris Anderson on April 12, 2009 at 5:14pm

Ah. You may be right. In that case, I'd go for gearing. You'll want you antenna on a pretty robust turntable anyway, and gearing is easy to add.

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Permalink Reply by Kyle Corbitt on April 13, 2009 at 11:04pm

There are a couple of approaches that are often used to solve this: using an "absolute encoder" that allows for the motor to always know which way it is pointed (generally in the relatively expensive $30-40 range) or have a means of calibrating the motor, which can be as simple as pointing the antenna due north and then hitting "calibrate."

If you think about it even using traditional, limited-rotation servos you would either need an onboard digital compass or to calibrate the direction your servos were pointed to begin with, otherwise your software will have no idea which servo setting is equivalent to which direction!

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Permalink Reply by Reto on May 14, 2009 at 12:25pm

Would it be possible to have some leds placed at fixed angles around the axis (maybe one North, and three others E, S, and W, or more if necessary) on the stand and an optical sensor turning with the antenna? At every light recognition (based on servo turning direction and led count), the angle could be recalibrated automatically. Just wondered while reading here.

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Permalink Reply by David Low on April 13, 2009 at 8:21am

great idea!!
it would be interesting to see the development of ArduTracker :)

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Permalink Reply by Scott James on April 14, 2009 at 5:14am

Great Idea! Can someone please do this! (My programming is no where near good enough yet!)

It could be set up to receive Raw NMEA Data so that any GPS or autopilot system could be used.
You would just need a "get home position" button on it which would involve putting your UAV down next to the antenna and pressing the button before take off! Then just point the antenna North and off you go! (using data modems of course)

It would be good to set it up to a standard Servo City type mount (or something cheaper), or have a feature where you could Scale / calibrate it to your own mount.

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Permalink Reply by Joseph Glanville on May 14, 2009 at 11:58am

You wouldn't even need to use an Ardupilot for this I would imagine, the standard Arduino boards would be perfectly capable of accomplishing this.
This is a brilliant idea however!
The concerns about zeroing the antenna are perfectly valid but the digital compass still seems a little overkill.. zeroing to north is a perfectly valid way of solving this problem but it might be tricky.
Even with some of the most directional of antennas, have a 10-15 degree beamwidth on both axis so at a decent range the antenna mount would not need to be super accurate.
An idea that just come to my head are telescope mounts, they would fit the bill for a mechanical platform almost perfectly.
Will post more after I have a think about it.

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Permalink Reply by Marty on May 14, 2009 at 9:29pm

Yes it should work on any Arduino board with minor adjustments. Nick suggested Ardupilot 168 boards as many of us already have them and they have now been made obsolete by the 328 boards and they have a small form factor.

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Permalink Reply by Joseph Glanville on May 15, 2009 at 1:48am

Yep makes perfect sense.
I will be beginning work on this shortly as I am going to need one for my current project.

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Permalink Reply by Joseph Glanville on May 14, 2009 at 12:51pm

Just found this topic:
http://diydrones.com/forum/topics/705844:Topic:46641
Collaboration is always best. :P

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