3 ms·

> Access 300+ flight data points logged every 1/10 of a second > View over 200 data points collected every 1/10 of a second during the flight Is there some si

> Access 300+ flight data points logged every 1/10 of a second > View over 200 data points collected every 1/10 of a second during the flight Is there some significance to these numbers (20 seconds and 30 seconds of data) or is that just an attempt at "big numbers sound good"?

defrost 4y ago
I wondered the same thing and looked a little at the DJI Drone family which seems pretty large and broad in application. The generic data channels number easily less than 50 - time, X,Y,Z, axis velocity, battery life, yaw, tilt, pitch, etc. I dare say some of the special domain applications generate more channels of data from mounted instrumentation - all logged to a common DJI family log format - for extraction on landing or broadcast during flight etc. The 200 channel Vs 300 channel thing is likely just poor copywriting from looking at max channels in two different application areas.
- mschuster91 4y ago
  There's also (probably) detailed logs from the collision avoidance sensors, as well as GPS. Even the relatively small Mini 3 Pro has six cameras and a downward-facing IR distance meter, the larger ones (Mavic 3) have even more cameras and ultrasonic short-distance sensors. At least from Reddit reports, the amount of data that these flight logs gather is more than enough for the customer support to determine a warranty case without sending the drone in (if that's even possible because the drone crashed into water and got lost). On top of that come RTK and ADS-B receiver data, and the really large ones (Matrice, Agras) add more engines, payload status (weight, flow rate), multi-battery health, RF quality and other data channels. To be honest, it's amazing just how many features modern drones carry while still allowing sometimes well over half an hour of flight duration.
dayjaby 4y ago
As a flight pilot engineer you have to find a sweet spot and balance logging too much and too little. Writing logs to an SD card has huge costs that come with it, that's why you don't want to log too much. Logging too little and you can't debug issues later on properly. PX4 also has lots of "topics" logged at around 1/10, e.g. hover thrust estimate every 100ms: https://github.com/PX4/PX4-Autopilot/blob/main/src/modules/logger/logged_topics.cpp https://github.com/PX4/PX4-Autopilot/blob/main/src/modules/l...
- LeifCarrotson 4y ago
  This has a lot to do with the performance of your processor. Running on a single-board computer with an applications processor like a Raspberry Pi or BeagleBone, with multiple cores at 1 GHz+, gigabytes of DDR3, with on-chip SDXC drivers? Logging loads are irrelevant. The only thing to watch out for is that if you want to use the logs to figure out why you had a catastrophic crash, the OS may have write-buffered a lot of data in RAM. If you're running on a crossover MCU, like a Cortex M7, with a core or maybe two at a couple hundred MHz? Think about it what you log. Running on a Cortex M3 with a few dozen MHz and a few dozen kB of RAM? Yeah, appending to and rolling over a whole 512-byte page in RAM and finding the time to push it over the SPI peripheral is going to be tough, you may want to use a binary protocol so you're not burning unnecessary cycles in itoa() and you get more data per byte of buffer. The DJI drones discussed here have big Cortex-A53 SOCs that are already logging 4k video at 30 FPS to that SD card; the log file is only noticeable as a distraction from that task. I think the crossovers are the sweet spot, though, because a 'fast' clock or interrupt on that Linux board is slow in comparison to the more tightly integrated RTOSes.
bnycum 4y ago
Just as a reference, I work on flight data recorders for rotor and fixed wing aircraft. 1/10 of a second is pretty common in that world as well.
electroly 4y ago
I've reread their statements and I'm certain they mean data series instead of data points. That is, there are 200 different types of data that they can collect from the logs (for as long as you have the storage to keep it), not that they can only store 20 seconds worth of data.

defrost 4y ago

I wondered the same thing and looked a little at the DJI Drone family which seems pretty large and broad in application. The generic data channels number easily less than 50 - time, X,Y,Z, axis velocity, battery life, yaw, tilt, pitch, etc. I dare say some of the special domain applications generate more channels of data from mounted instrumentation - all logged to a common DJI family log format - for extraction on landing or broadcast during flight etc. The 200 channel Vs 300 channel thing is likely just poor copywriting from looking at max channels in two different application areas.

mschuster91 4y ago
There's also (probably) detailed logs from the collision avoidance sensors, as well as GPS. Even the relatively small Mini 3 Pro has six cameras and a downward-facing IR distance meter, the larger ones (Mavic 3) have even more cameras and ultrasonic short-distance sensors. At least from Reddit reports, the amount of data that these flight logs gather is more than enough for the customer support to determine a warranty case without sending the drone in (if that's even possible because the drone crashed into water and got lost). On top of that come RTK and ADS-B receiver data, and the really large ones (Matrice, Agras) add more engines, payload status (weight, flow rate), multi-battery health, RF quality and other data channels. To be honest, it's amazing just how many features modern drones carry while still allowing sometimes well over half an hour of flight duration.

dayjaby 4y ago

As a flight pilot engineer you have to find a sweet spot and balance logging too much and too little. Writing logs to an SD card has huge costs that come with it, that's why you don't want to log too much. Logging too little and you can't debug issues later on properly. PX4 also has lots of "topics" logged at around 1/10, e.g. hover thrust estimate every 100ms: https://github.com/PX4/PX4-Autopilot/blob/main/src/modules/logger/logged_topics.cpp https://github.com/PX4/PX4-Autopilot/blob/main/src/modules/l...

LeifCarrotson 4y ago
This has a lot to do with the performance of your processor. Running on a single-board computer with an applications processor like a Raspberry Pi or BeagleBone, with multiple cores at 1 GHz+, gigabytes of DDR3, with on-chip SDXC drivers? Logging loads are irrelevant. The only thing to watch out for is that if you want to use the logs to figure out why you had a catastrophic crash, the OS may have write-buffered a lot of data in RAM. If you're running on a crossover MCU, like a Cortex M7, with a core or maybe two at a couple hundred MHz? Think about it what you log. Running on a Cortex M3 with a few dozen MHz and a few dozen kB of RAM? Yeah, appending to and rolling over a whole 512-byte page in RAM and finding the time to push it over the SPI peripheral is going to be tough, you may want to use a binary protocol so you're not burning unnecessary cycles in itoa() and you get more data per byte of buffer. The DJI drones discussed here have big Cortex-A53 SOCs that are already logging 4k video at 30 FPS to that SD card; the log file is only noticeable as a distraction from that task. I think the crossovers are the sweet spot, though, because a 'fast' clock or interrupt on that Linux board is slow in comparison to the more tightly integrated RTOSes.

bnycum 4y ago

Just as a reference, I work on flight data recorders for rotor and fixed wing aircraft. 1/10 of a second is pretty common in that world as well.

electroly 4y ago

I've reread their statements and I'm certain they mean data series instead of data points. That is, there are 200 different types of data that they can collect from the logs (for as long as you have the storage to keep it), not that they can only store 20 seconds worth of data.