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
Well said Joe. Thank you.
I've posted my findings and conclusions regarding heat interference in a new blog here http://diydrones.com/profiles/blogs/temperature-changes-can-cause-u...
IMHO open source hardware and open source software means the entire community is involved; it means that as the community finds the problems, the community also finds the solutions and then they are incorporated into the hardware design to improve it. Each member of the community contributes as they can and want to. The caveat to buying a community designed device, even from a commercial operation that has decided to produce it, is that it *may* have inherent bugs that have not yet been found and that the manufacturer is not, IMO, responsible for - they are producing the communities product, not their own in-house proprietary product. The manufacturer is, however, responsible for exercising reasonable care in the production process, something I believe 3DR accomplishes nicely.
Just my 2 cents worth, FWIW.
I think your response is a little stronger than I would support. I don't really intend to discuss the meaning of DIY, fault or responsibility here. I'm just testing, learning and contributing what I have learned.
I also can't call this a hardware issue. All of the sensors (hardware) are performing exactly as they should. Unfortunately we just aren't giving the sensor a noise and interference free environment. I hope that my testing will help everyone learn how to better protect their APM from unwanted interference.
Thanky J B for this real huge eye opener!
Please keep on investigating!
This was areal WTF moment for me!
Just a few questions popping up in my head:
Maybe i do get this wrong, bit as i read this EVERYBODY since the first APM 1 is more or less affected, depending how good you boxed your board with lightproof containment?
Why the heck does 3drobotics no accurate testing of their widely sold equipment?
Why do'nt they just stick the head up and look around?
E.G. Asctec solved the baro issues many years ago with just some plastic shrinktube and foam around the baro.
regarding gyro issues 2 degrees is not much at all why not just keep it at temperature or thermal isolate for slow temperature change. Possible solutions are there, but wihout testing you will not find the problem.
Why does the community have to find out about such circimstances?
Why are the prices that high if not even the sensors are well tested for the intende use?
Just grab some availiable sensors layouting a pcb and selling this at high price, ey?
For the salve of conscience put the links to the datasheets of the sensors in the shop.
(just an assumption, i can not proove that)
This cost many people a huge amount of money, not to mention the people put in danger, maybe this was even on purpose to sell more parts stuff?
This clearly is a hardware issue!!! So maybe a callback and/or fix would be the right approach? At least a cost and shipping free diy solution kit for every APM a customer bought?
I do not think that diy in this case means every customer has to fully retest his bought product for the application especially if you buy rtf or kits.
Again, Open Source Hardware does not mean you can offload functionality and safety testing to your customer, especially if the flight controller is sold as ready to use product!
Any one else having such toughts or am i completely off track here?
It doesn't seem to be a set amount of time before the INS command and MP locks up. Sometimes it's 15 minutes sometimes its a few hours. When I was initially testing I was not seeing failures for a few hours. (As the gyro sloooooowly heated on my table.) CLI wasn't the most useful for this as I was trying to set it to run and come back to check on it after work. I did think of using a terminal program but never got back to it.
Would the raw values be of use to everyone? I can do some testing on that this weekend.
Like how long? I have run those test for a few hours at a time.
You can also connect a terminal program and access the cli that way as well.
@Craig Elder I actually tried that but the mission planner seems to crash after streaming the raw data for a while. It was what I first used in testing but couldn't really use for the videos. (It might just be my mission planner but I didn't troubleshoot it further.)
JB, you might find it interesting to run your tests from the cli where you can examine the raw sensor values discretely without the sensor fusion running.
Go Terminal
Connect APM
test
If you type help you can see a list of options.
ins will show you the raw accelerometer and gyro values
baro will show you the raw barometer and temperature readings
@Tom Mahood
1. I'm not sure. I only own one APM so I can't make any comparisons. I experienced some random roll overs from prior to 2.8 so I think I've had this problem for a while.
2. I haven't tried to figure out exactly how much of a difference makes for a change. I know that more difference doesn't necessarily mean worse values.
3. I added the liquid electrical tape to the APM recently. As the rubber coating is above the already existing foam I don't think this would make a huge difference.
4. Yes I believe it can. I fully assembled my quad list night after testing. Took it outside. Let it sit for about 2-3 minutes and then flew with no problems. Altitude hold and loiter both performed beautifully.
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