I’ve been curious about what installation conditions I need to worry about when building my APM based quad. We are all very aware of how magnetic interference affects the compass but I was curious how different light sources, magnetic fields and heat affect all of the IMU sensors.
https://www.youtube.com/watch?v=MrEPsA34daY
I did some testing on my workbench. This is by no means an “experiment” as I was rather lackluster in controlling outside variables and I certainly didn’t run the test more than a few times. (Basically I ran each test once off camera just to make sure I wasn’t going to make a video of nothing.)
You will notice a distinct lack of accelerometer data in the videos. That is simply because I couldn’t seem to cause any interference to the accelerometers with light, magnetic fields or heat. I chose to ignore that portion of the IMU for my tests.
What I learned from this was that I need to put additional light blocking materials to the sides of my APM. I did some testing with the case on and light definately leaks in through the foam from the sides. I was surprised how much of a difference it made. I’ve experienced altitude loss during aggressive maneuvers with Alt Hold and I wouldn’t be surprised if this was contributing to the issue.
I also learned that heat affects the gyro. I’ve had a few roll over issues recently that have been diagnosed as a bad gyro. (I’m only 90% convinced that it’s a bad gyro. It will work perfectly for weeks and then just go nuts. Once it goes crazy it will only stay broken until the APM is power cycled.) I normally do my test flights outside of my home. This would involve cold power on in a 72 degree work room followed by a transition to a sunny 80+ outdoors. I’m going to do additional testing on this to see if I can reproduce my exact issue with heat only in controlled conditions.
Let me know if you have any other questions about my tests or if there is anything that I should investigate further during my next round of testing.
Also, some gratuitous FPV flight from my other quad.
Comments
@J B: Excellent post. Several questions: What are the units on your temperature readings? (I'm assuming you're using degrees Fahrenheit.) Secondly, based on your post, I wanted to confirm that you're getting post flight case temperatures of ~125 degrees from an ambient air temp of 80 degrees.
OK I should have watched the video first.
Which values are displayed as graphs? Are these gx, gy and gz or pitch, roll, yaw? I think you must consider that the raw gyroscope values are the ones of the 16-bit ADC. You have a measureable range of +-2000°/s which are converted in a span of 2^16 = 65536 values by the ADC.
So when you see some small temperature dependencies I think these are negligible. Maybe you can check this once more but with the tuning parameters pitch, roll and yaw? That would be interesting for me.
Regards
Hi,
how did you exactly notice that the gyro is affected by heat? I'm performing some APM sensor testings aswell. I put the APM into a climate chamber and brought the temeratures from -20°C to + 50°C and the gyros and acc-sensors didn't show high fluctuations.
Martin
That's really interesting. The baro's sensitivity to light is something that I've recently heard so it's great to see a video clearly showing it. I think this is something that we need to publicize to everyone along with some instructions on how to protect against. I've heard black electrical tape on the APM2.5 case works.
The gyro's sensitivity to heat is something I've never seen demonstrated although Ryan Beall produced a paper showing the impact on his system's gyros (which are different from the APM's).
Great, contribution!
Really interesting, thanks for sharing this!
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