IMU Mid-Air Reset
I'm getting closer and closer to being ready to test my UAV, but I still have one failure case nagging the back of my mind: what to do if the board resets in mid-air and clears the DCM matrix? I mean, I don't plan on having mid-air resets, but what if it happens?
I've played with the idea of writing the position to the EEPROM every once in a while, but it would have to be very often given how much orientation can change in a second. And given certain instabilities in the flight characteristics, I don't trust it not to crash while the accelerometers slowly sort out the gyroscopes if it resets in, say, a 45 degree bank.
What methods have some of you employed to deal with a mid-air reset of your IMU variables?
Thanks!
Replies to This Discussion
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Permalink Reply by DaveyWaveyBunsenBurner on -
Mid-air resets are covered in thhe code but need to be enabled i believe. The APM sees ground speed via GPS and doesnt reinitialise the IMU. Im on a crappy phone with a tiny screen at the momont but seem to remember enable_air_restart can be set??
Sorry if i misunderstood your question.
D
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3D RoboticsPermalink Reply by Chris Anderson on -
I think answer is the same for all multicopters: if the controller board crashes, the copter will too. Unlike planes, which can revert to manual control while the board restarts, multicopters aren't controllable without the IMU. Even a one-second reboot time is probably too long to regain control unless you're flying pretty high.
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Permalink Reply by malcolm churn on -
Yup i can safely say if you have a mid air reset, you are going to crash.
It happened to me when my board did it according to the logs four times. not nice seeing the heli doing flips and rolls.
Least i know what the problem was.
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Permalink Reply by DaveyWaveyBunsenBurner on
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Sorry, thought we were talking fixed wing!!
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Permalink Reply by David B on -
We are, actually. I'm using the ArduImu board but not the accompanying code - its part of my project to write the code myself. So should I just have it assume its something close to level whenever it starts?
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3D RoboticsPermalink Reply by Chris Anderson on -
Ah, sorry for the misunderstanding. With fixed wing it's pretty easy. On APM we have a whole system for this, called "air start" that does a fast reboot that retains last calibration settings. Works great.
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Permalink Reply by Michael Pursifull on -
If you have a few seconds, would it be possible to run a few calculations with the accelerometers? If it is fixed wing, then can assume forward airspeed. I wonder if it is mathematically feasible to isolate your vector, then "look" for the earth's gravity, then compute for best-guess of perpendicular to ground? Without GPS speed/position data, I do not think it is practical, but given that you are 1) fixed wing 2) forward motion (and more motion) and 3) have streaming GPS speed and direction from which the vector might be taken, I wonder if it is possible. Or is that a masters thesis in INS?
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Permalink Reply by DaveyWaveyBunsenBurner on
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Assuming we are talking actual IMU resetting, and not autopilot, I would imagine you could, you have no idea what the actual attitude is so level is as good as any guess :) have you had a peek at the existing code for clues??
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