We managed to get our hands into a Raspberry Pi 3 and decided to give APM a try with it using the PXFmini. Here’s a walkthrough over some of the tests that our team conducted: 

Benchmarking

So, down to the benchmarks, we performed 3 types of tests using sysbench and the default Raspbian images (no APM running for now). SysBench is a modular, cross-platform and multi-threaded benchmark tool for evaluating OS parameters that are important for a system running a database under intensive load. The output of sysbench looks like this:

sysbench --test=cpu --cpu-max-prime=20000 run

sysbench 0.4.12:  multi-threaded system evaluation benchmark

Running the test with following options:

Number of threads: 1

Doing CPU performance benchmark

Threads started!

Done.

Maximum prime number checked in CPU test: 20000

Test execution summary:

   total time:                          477.3324s

   total number of events:              10000

   total time taken by event execution: 477.3236

   per-request statistics:

        min:                                 47.69ms

        avg:                                 47.73ms

        max:                                 85.54ms

        approx.  95 percentile:              47.72ms

Threads fairness:

   events (avg/stddev):           10000.0000/0.00

   execution time (avg/stddev):   477.3236/0.00

 

The output is graphed against the Raspberry Raspberry Pi 2 (note that smaller bars indicates better results):

sysbench --test=cpu --num-threads=1 run



sysbench --test=memory run --memory-total-size=2G

sysbench --test=memory run --memory-total-size=2G --num-threads=1 --memory-oper=read

The 64 bits CPU of the Pi 3 dramatically improves the results of this particular tests over the Pi 2. It’s 40% - 60% faster.

Mounting the autopilot:

We mounted the shield as follows which proved to be robust enough. Vibrations were kept at a reasonable level as will be shown later in the log analysis:

Flying with APM and log analysis

After a short flight we started some checks. The official documentation of APM will tell us:

“Check the scale on the left and ensure that your vibration levels for the AccX and AccY are between -3 and +3.  For AccZ the acceptable range is -15 to -5.“

Fine on this. We also felt that the drone was reacting really good so made a few plots that convinced us about the autopilot responses with the Raspberry Pi 3:

 

Conclusion

Raspberry Pi 3 is a great candidate to make APM Linux autopilots using the PXFmini!. Having Bluetooth and WiFi is indeed a great asset removing the need of using additional USB dongles unfortunately, WiFi is solely b/g/n and does not support the 5 GHz frequency band (which comes handy when flying with RC controllers that work in the 2.4 GHz band).

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Comment by JB on March 3, 2016 at 6:47am

Lol Jerry. Do you mean this one that RS carries still (and element 14 etc):

http://au.rs-online.com/web/p/processor-microcontroller-development...

---

@Victor

There's a new compute module coming with the 64Bit Pi3 hardware.

Jurgen from Auvidea is already making boards with PXH2, Edison and TX1.

If another version of the PXF is made I'd really like to see a MCU instead of the PCA. Plus it will be necessary to route out both some USB and the MSI for camera etc use. With the SO-DIMM slot connections of the compute module I'd try to keep it as compact as possible for small frames. It should also follow the same schematic as the existing module, so it's possible to get a head start now already before it comes out. It could be marketed as the "improved version" of the Zero PXFmini, with computer vision, for only some $35 more. (the cost of the Pi3 Module over Zero).

Layout wise I'd have the 2x USB/MSI up one end for camera/ext. wifi with PWM/RC up the other end for ESC etc. It's also possible to integrate a 4ch ESC in the same form factor as a extra daughterboard underneath the PXF for super compact setups with 3 stacked PCBs (under 50g).  

Regards

Comment by Paul Meier on March 3, 2016 at 7:48am

@JB, I agree that the new Raspberry compute module if it will feature the new SoC of the Pi3 should make an excellent cheap CC. 

I have the old version and I am very happy with it, it has a very small footprint

Comment by Lander Usategui on March 5, 2016 at 5:39am

The OS is available for download on our docs. In case you want to try it.

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