Greetings,
I was wondering if the Nav board will work without the GPS module? My main use would be for improved flight performance (stabilization mainly). I have several planes and I'm going to put the full setup with GPS in one of them, but if it works without the GPS I might go that route for the other planes (versus moving stuff from plane to plane which seems like a bad idea). Thanks in advance!
Best regards,
Mark
Replies
If I interpret your question correctly, what you need is called a stability augmentation system (SAS).
Aviation Dictionary: stability augmentation system
Top Home > Library > Cars & Vehicles > Aviation Dictionaryi. An autostabilizer system that is essentially a damping device incorporated in most helicopters (and some airplanes). The stability augmentation system enhances stability but does not have the ability to hold a given datum.
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The question implies that you want a tight and stable response from the plane while it is under manual control.A simple SAS does not require accelerometer feedback loops or use of the DCM attitude reference frame. A satisfactory implementation would consist of including a simple gain transfer function in a stick to surface to rate feedback loop in each of the pitch and roll axes. It would involve blending the stick (manual flight mode) inputs with the rate gyro outputs (negative feedback) . Start flight test with unity straight through gains (fly-by-wire) and fade in the feedback in small lincrements.Include a panic switch. You should be able to get what you want with a few handsfull of code lines. The fundamental SAS pitch loop on the F/A-Hornet used around 250 16bit words of memory. You would have to reload an unaltered version of MatrixPilot and connect the GPS for UAV applications.
If you pursue this I would like to keep up with the results.
Mike Cowan
Did anybody actually released the code for UAVdevboard that enables it to work in STABILIZATION MODE without a GPS module connected to it?
Thanks!
We had a discussion about this on the uav-devboard list in early March.
The gist of that discussion was that providing you make the UAV DevBoard believe that it is travelling at a speed slightly greater than the normal flight speed of you plane, then you can probably do this. Flight Speed is required to take account of G forces in tight turns. The on board accelerometers are vital for continually correcting the roll and pitch gyros. The accelerometers feel the pull of gravity. However, in a continuous turn, the gravity vector cannot be accurately found unless the firmware subtracts the pull that is felt by turning from the accelerometers. In order to calculate the turning pull, the firmware needs to know two things 1) The rate of turning (from the gyros) and 2) the speed of the plane. The speed is normally provided by the GPS unit. However it would seem that in practice, you can simply provide a rough statically defined estimate of the speed (e.g. 10 m / s for many small model planes), and the calculations will be sufficient to keep the plane stabilized in pitch and roll.
More detail in the discussion thread referred to at the beginning. This feature is not currently in the firmware. It would not be too hard to add it.
Pete