Hi folks
I have had two crashes with APM 2.5 - both with identical symptoms.
All functions will work normally, and then at a certain point (seemingly randomly) the following will happen:
- All RC servo control is lost - aileron, elevator, rudder.
- OSD continues to function, with GPS and altitude/speed data.
- According to logs, APM is continuing to function and record data (accelerometers etc)
- Throttle control (both RC and autopilot) continues to function.
The servos appear to reset to their neural position and I am unable to control them regardless of mode. I have tried stabilize, FBWA, manual and RTH and in all of these, I am only able to control the throttle. In RTH the plane throttles up, but does not turn.
This has resulted in the plane slowly gliding down into a crash in two separate instances.
Please see this youtube video, recorded from a friend's goggles (hence the poor reception): http://youtu.be/u81nDJ-BJDI - control is lost at approx 0:55 in the video.
Here is an image of the plane's flight path. As you can see everything was going well in FBWA (purple). I then attempted to switch modes to regain control, first into stabilize, then into RTH and eventually stabilize again.
Things which I have noted in my troubleshooting steps:
- Battery voltages were good - above 3.7v per cell on 4S.
- I had just completed a 'fast pass' at 40% throttle for 7-12 seconds. This may have placed additional load on the power system or servo's. (Note that cruise throttle is 20%)
- My OSD flickers on and off at around 0:35 in the FPV video linked above. This may indicate a voltage drop?
Information on my setup:
- Skywalker Revolution FPV airframe
- APM 2.5 with power module, running ArduPlane 3.2
- JP1 jumper disconnected
- 4x Servo's connected to APM output, along with 40A ESC BEC supplying power.
- Modules powered by APM: GPS, Compass, X8R receiver, MinimOSD 5v
My theory is that the combined draw from GPS, Compass, X8R receiver, MinimOSD and the APM board itself has overloaded the 500ma power circuit supplied by the power module, shown here:
I have found some similar issues experienced by another member who was trying to run pan/tilt servo's from the APM board, here:
My question to the experts is - does this seem like a plausible explanation, or should I be looking elsewhere to troubleshoot? I would like to avoid a third crash!
I have attached the log files for the most recent flight.
Thank you for your help!
Replies
I've performed some bench tests and have found there is a voltage drop on the APM side when all modules are connected. Here are my findings:
With only apm connected to power module
Power module output: 5.49v
Apm board voltage: 5.14v
With apm, GPS, compass connected
Power module output: 5.49v
Apm board voltage: 5.08v
With apm, GPS, compass, x8r receiver connected
Power module output: 5.49v
Apm board voltage: 5.02v
With apm, GPS, compass, x8r receiver, MinimOSD connected
Power module output: 5.49v
Apm board voltage: 4.96v
When simulating flight: prop on, 35% throttle, all modules connected, voltage drops to 4.95v on APM board side.
The voltage on the output-side of the board stays constant at 5.07v, regardless of servo load, prop spinning, etc.
Would this voltage drop be sufficient to cause the board to brown-out, crash, or otherwise behave weirdly?
If so, should I simply add a BEC to the APM-side to boost the voltage and reduce the load on the APM voltage regulator?
Thanks