Pixfalcon configuration and use

Starting a new discussion about the Pixfalcon and their configuration, since there’s very little information out there and almost everything assumes they are a complete “drop-in” replacement for a Pixhawk.

I’ll start with my config:

Pixfalcon, via Hobbyking with SD card, Micro M8N GPS, “Ideal Power” PDB and wiring

QGroundControl for config and missions

Firmware: PX4 1.6.3 stable
Airframe: Generic quadrotor X with gimble
Wheelbase: 510mm across opposite motor shafts
Construction: 4 square section aluminium arms 23mm, top and bottom plastic decks
Motors: NTM Propdrive 28 1000KV x4
Props: 9x4.7 slow fly, Generic plastic at this stage
ESCs: unknown, I presume at least 30amp and capable of at least 4 cell, maybe 6 cell
Battery: 3cell 3000mAh Lipo Turnigy Graphene with XT60
Camera: GoPro Hero, fixed gopro mount
FPV: none yet, camera and 5.8GHz radios planned
TX: Orange RX T6 mode 2
RX: Orange RX R615

The frame, ESCs, brushless outrunner motors, LED strips and some associated wiring was donated “as is”.
The motors mount directly on the arms via drilled holes and mounting bolts.
I’ve added an aluminium spacer to top and bottom of each arm to space the top and bottom decks further apart, allowing for the receiver to be mounted in there, plus more room for the PDB and wiring. The decks are now about 18mm apart.

Top Deck:

  • Front and center is the Pixfalcon on two foam blocks supplied with it.
  • Rear is the GPS unit on a home made perspex open-sided cube, giving the GPS about 40mm extra height.
  • The safety switch mounts in this cube facing rearward, and a USB extension connector
  • right side is the battery voltage monitor with alarm, plugs into the balance leads
    Middle Deck:
  • PDB in the centre, wires out to each ESC mounted on the arms as far inboard as possible
  • Receiver to the left side so the small antenna wires poke out away from the decks and PDB
  • Battery XT60 connector hangs out the right side
    Under Deck:
  • The battery is velcro’d and strapped to the underside rear.
  • The Gopro mount is also stuck underneath and the camera hangs down.

We use the battery voltage monitor as insurance since we had previously issues with setting the voltage measurement in the Pixfalcon with the standard PDB and currently there’s no FPV or telemetry, we need to be able to hear the alarm!
Once there was a power loss and fall from about 30m altitude, no damage except a couple of broken props.

I’ve changed out the standard PDB for another I got through HK, a Holybro PDB with UBEC and OSD v1.1 - the advantage with this one is it has inputs for the motor PWM outputs from the FC and outputs to the ESC’s, thus getting rid of all the 3pin connectors on the standard Pixfalcon wiring. I was able to cut and terminate the 3 pin BEC wires from the ESCs and just connect the signal wires to the PDB, along with main power wires of course. Wiring is now much neater.
Also I was getting inconsistent voltage sensor readings from the original unit, and the Holybro seems slightly more stable
The OSD wiring is plugged into the Telem port of the Pixfalcon, but we dont have a FPV camera or radios yet and so the OSD functionality is not tested at this stage.

Currently the landing gear is home made from garden irrigation risers - they actually work quite well with enough flex for rough landings but strong enough to support the overall weight. Original legs were short perspex, 1 from each arm near the motors - they’d snap off if there was any sideways movement during landing or takeoff. Need to get some real landing gear organized…

The Pixfalcon came with some version of PX4, cant remember which version but it worked “out of the box” with QGroundControl and we were able to configure the quadcopter and it would fly well after we figured out the motor order and rotation.
I’ve recently tried the latest version that QGC automatically downloads and installs, but after config we couldn’t get the FC armed for unknown reasons, I manually downloaded and installed px4fmu-v2-default 1.6.3 and was able to fly straight away and we haven’t had to customize any special parameters.
Got to spend more time working with logs so I know what I’m looking at when/if there are issues.

Great! Stable! No issues. Missions work as expected.
We use Stabilize, Position, Mission and RTL,
Low voltage action is set to Land.
Ascent rate is AWESOME!
I’m unsure of the weight, but with 4 1000KV motors and a fairly minimalist setup, it’s almost like a racer or acro quad rather than a video platform. Flight time is around 18 mins - we keep forgetting to record it accurately.

Orange RX T6
3 flight modes on the 3 position “Flaps” switch, channel 6
RTL on the “Gear” switch, channel 5
Zippy Compact 850mAh 2 cell

I know, it’s a PX4 forum… Thought I’d throw this in to demonstrate how good PX4 is.
I was able to set up the ORX T6 to suit flight modes in Arducopter firmware by mixing channel 5 and 6 and output to channel 5 - Arducopter will ONLY use channel 5 for flight modes. With the two switches in combination Arducopter would pick up 5 modes using this method, might get 6 modes with a bit more fiddleing. I mention it because there’s almost no info regarding flight mode switches on the T6 (and no way to assign channels to switches) and no way to change the flight mode channel in Arducopter/MP/APM2.
Anyway - I’ve tried to get Arducopter working on the Pixfalcon a couple of times without any success - I came straight back to PX4 and everything just works. We miss out on Spline way points, circle mode, drift mode and a couple of other cool things but nothing we cant live without.
Arducopter on the Pixfalcon gave very poor results. It would not arm even after getting a GPS fix after about 10 mins, or if it would arm the motor outputs would be “random” with only 1 or two motors working, none working, or motors out of control with a mind of their own.
GPS fix was almost never obtained, or it took an extreme amount of time. The GPS unit would show a fix, the FC would not.
Once it lifted off to about 1m height and flew for about 2 seconds, but after landing it refused to fly again.
I’ve tried the latest couple of Arducopter versions, but I haven’t gone back very far so maybe there is a version out there that works. From what I’ve been able to find there’s customization you can do in the parameters to get the Pixfalcon and Arducopter working somewhat, but it’s not perfect and is a heck of a lot of messing around.

For Pixfalcon, stick with PX4 and QGC - it just works.

For those interested, the QGC params “Save to file” and “Load from file” in QGC works perfectly.
I had been trying more versions of “that other firmware” and not getting anyware, I reloaded PX4 fmu2 as per above and reloaded the params OK.
Another reboot was required to put all the default params in place, then reloading the params again to ensure all were back to their original values.
Flight test was perfect, no recalibration or anything required.

A small win: I was able to flash PX4 FMUv2 1.6.5 via the automatic firmware process in QGC and get a working Pixfalcon and quadcopter.
The step I’d previously been missing was recalibrating the ESCs - I’m not sure why it was required since the other calibrations seem OK. The ESC calibration in QGC worked fine, no need for manual calibrations with transmitters and receivers working in concert.
Past attempts at using the newer firmware, the odd motor behaviour had made me think that all sorts of major things were wrong. We’d even rerun all the calibrations and setup - except the ESCs! A trap for the young players I guess.
Something that reinforced the assumption that the new firmware wasnt working on the Pixfalcon was the fact that I didn’t need to recalibrate the ESC’s (or anything else) when I’d go back to firmware 1.6.3 - it just worked.

So pending more flight tests, PX4 1.6.5 works on a Pixfalcon

Pixfalcon PX4 1.6.5 flight test ok after the above-mentioned ESC calibration. No other calibrations required.

Great posts. I bought a couple PixFalcon kits last summer, and aside from the need to splice cables for integrating GPS, airspeed, etc., I had very good luck with mine.