Tracking - Pan scale


I set up an ardustation with JR servos, installed on a home-made pan-tilt base. I set the pan servo limits to match the station gear ratio, and by using the antenna test screen I get perfect 360 deg rotation. However, when operating, I start with the antenna pointing at the plane, but when moving to the sides, the antenna deflects more than required.

At first I thought my limits were not set correctly, but I ruled that out by setting them up several times. Also, when circling the station, when I reached 360 deg, and the station had to make a full circle to 0 deg, it did so such that 0 was aligned with 360, without overlap with the other travel end. This, to my understanding, also demonstrates that the travel is set properly. Moreover, it shows that the antenna is pointing to where the station wants it to, and not someplace else due to mechanical setup.

If this is true, then the station is might actually be giving wrong commands. I realize this is unlikely, since people use this station successfully. Any idea what I should check?



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  • IThanks for the reply.
    I get 9-10 sattelits, and I do fly in a large are, with no obstrations (fields).
    The problem is indeed consistent.servo seems to be linear as I test the station through the antenna test screen.
    Any other ideas?
  • When you're doing the test how many satellites are being received? If you're close to the aircraft, multipath issues with buildings nearby can pollute the solution and cause errors in pointing also. If the errors are consistent, it is also possible that your servos are operating in a nonlinear range of pwm values. The software assumes linear rotation through the whole 360 degrees of rotation. Data errors on the link would show extreme errors in pointing that would be very inconsistent.

    The best way to test is in a large open field and to carefully compare the pointing angles vs expected angles and check for nonlinearity.
  • I forgot to mention - I am not using an XBee modem, but rather an 2400 bps modem ( The connection with the station seems to be ok, but now I fear that somewhere on the data path the plane position data is damaged.

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