J B's Posts (3)

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Temperature Changes Can Cause Uncontrolled Roll

Short Story:

As this video shows the APM gyro is sensitive to heat changes after it is powered on. Be careful that you allow your APM to acclimate to the flying conditions before powering it up for the first time. This doesn’t seem to take more than 5 minutes but this is only for my specific quad configuration. Since everyone’s quad is different yours might take shorter or longer. My startup cycle and preflight checks now have me removing the quad from the vehicle\building\shade and placing it in it’s takeoff point as the first step. I then proceed to unpack batteries, transmitter and other gear. This give the APM a good chance to warm up or cool down before it is powered on for the first time.

Long Version:

During my tenure with the APM I’ve had a few odd crashes. Once while flying outside of my office with a cell phone camera zip tied to the frame it started rolling to the side uncontrollably. I wrote this off the the cell phone shifting.

A few weeks later I was doing some testing just outside my house. I had another uncontrolled roll. This time I was much lower and it wasn’t too hard to land before it flipped.

Crash three was again just outside of my office. I was testing simple mode at lunch. Another uncontrolled roll. (By this time I’m getting good at landing it with minimal damage.)

Crash four was after my MuMetal testing. I had taken it just outside of my house again for some loiter testing. Again it rolled uncontrollably.

During the last crash I had all of the logging on. I was linked to my laptop and even got tLogs. This time when I carried my quad back into my house (without unplugging the battery) I was able to see that the quad thought it was rolling to one side continuously even though it was just sitting on my desk.

I powered off the APM and powered it on via the USB interface with the intent of viewing the raw INS data from the terminal. Unfortunately when I began streaming the raw data the gyros looked just fine.

The next morning I plugged in the APM and began streaming INS data. My intent was to check on it during my lunch and see if it failed after a certain amount of time. Unfortunately when I came home for lunch the mission planner was locked up and no new values were streaming. I clicked on my workbench light, rebooted my laptop and started the INS test command again.

I came home from work to check on my test but mission planner was again crashed. This time the last value displayed on screen was a bad gyro value! I had seen failure! (I didn’t know it at this point but my workbench light was the key.)


At this point I began to assume that my APM had failed but only slightly. I didn't want to trust it in flight but I could use it as a testbed for other projects. I took everything apart and decided to do some random testing.


I hope all of this information helps someone. I’m not sure if this is appropriate to add to the wiki as a preflight step.


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Testing Other APM Interference Sources

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.


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.


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MuMetal Testing

I’ve been trying to clean up magnetic interference from the motors on my quad. When I run compassmot I get any where from 100% to 130%. I ordered some MuMetal and did some testing to figure out how to best use the metal and to see exactly where interference was coming from.

All of the flight electronics were removed and temporarily installed under the frame.

Here are the specs of the quad used:
3DR Quad frame Rev C
APM 2.5 running 3.0.1rc1
3DR AC2830-358 850KV motors
3DR 20A ESCs
APC 10x4.7 props
3S 6400mAH battery
Spektrum AR8000 Rx
3DR 900Mhz Telemetry

My transmitter is a Spektrum DX8

I used an old compass I have left over from my boy scout days and the magnetometer within my cell phone. (The app is Sensor List Pro).

The fields generated by the wiring, ESCs and battery all seemed to be about the same relative strength.

The MuMetal does have a small magnetic field of it’s own. It’s not very strong but it is there. (Notice how the compass point angles toward the MuMetal). In later tests I put a small amount of space under the compass.

I think I’m going to end up with my APM about 22mm above my wiring with a MuMetal sheet at about 19mm. I may consider also attaching a small MuMetal sheet to each ESC on the top as they seem to be quite magnetically noisy.

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