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Aug 23, 2012, 09:37 PM
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Sonar flights continue

After all that work on making a high frequency amplifier, test flights once again led nowhere. It was definitely better than air to ground pings, but much less accurate.

The latest thing is instead of recording & replaying telemetry files, making video of the ground station.

In 2007, you couldn't make video of a screen because AGP was unidirectional. That motivated a lot of investment in flight recordings. PCI express once again brought back the bidirectional speed to allow the screen to be recorded.

The most successful flight showed clear circling around the target position. The sonar successfully tracked it flying below 1 meter, in a 2x2 meter area, with 0.2 meter accuracy, but the feedback couldn't dampen the oscillation.

The sonar range is much less than air to ground. The omnidirectional motor noise is always near the airborne receiver, while it has a chance to diffuse before it hits a ground based receiver.

For confined, indoor use, sonar once again is best suited to a horizontal receiver array on the ground with an airborne transmitter that always points sideways to the array. It might still work for a monocopter, in which the aircraft has a couple pings per revolution which are always guaranteed to hit the ground array.

Going back to vision for daylight operations, Centeye is too expensive for any product, but a cheaper camera might be able to simulate the same high speed, low resolution magic trick, at a lower speed.

The idea with a low resolution camera is the high speed allows you to detect a flashing LED. Aim the camera so a flashing LED lands right in the middle of 4 pixels. As long as all 4 pixels are illuminated as equally as possible, you can get the position to a much higher resolution than the camera's pixel count.

This depends on the camera either not having a lowpass filter or the pixels being binned in software without any lowpass filtering. It also depends on having a very accurate, fast pan/tilt mechanism.

In reality, it's never going to land exactly between 2 pixels. It would take a very high frame rate, lots of position averaging, with the camera turret constantly orbiting around the target, so the LED splits 2 pixels as much as possible.
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