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Feb 28, 2013, 02:34 AM
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PX4Flow test 1


With the PX4Flow connected to USB & Qgroundcontrol fired up on a Mac, it was immediately clear that it had a very long, sharp, macro lens, allowing it to resolve texture from far away, but also limiting its useful altitude to 0.5m to infinity & requiring a very high framerate. The image is a 64x64 window in the middle of the sensor.

Setting it to low light mode produced a noisier image. In any mode, the position updates only said 90Hz even though it's supposed to do 250fps. Maybe it accumulates readings. There was no obvious update rate parameter.

It didn't seem to compensate for angular movement. According to the mavlink source code, flow_comp_m_* is the angular rate & altitude compensated motion in floating point meters. flow_* is the raw number of pixels moved. The usual limited range readings over carpet of the Maxbotix sonar appeared.

It didn't need any calibration. Just connect it & it outputs Mavlink position packets. The lens was already focused. It outputs packets at 100Hz on USART 3 but not USART2. It seems to run as low as 3.3V at 120mA. Below that, current drops & LEDs start going out. Above that until the 5V maximum, current is constant.

Not having the right variation of micro USB connector is a drag, but there's nothing to do on qgroundcontrol besides test the focus & convince yourself low light mode is worthless.

The same thing could probably be done for a lot less weight with the TCM8230, windowing a 64x64 area to get some textures. It would require a large grid pattern on the floor while the PX4Flow could get away with linoleum.

Flying with such a large lens pointing down is an expensive disaster in the making, but it's not clear if optical flow is going to be important enough in the long term to justify doing it from scratch.
Last edited by Jack Crossfire; Feb 28, 2013 at 05:23 AM.
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