Pixhawk Details #1: Overview of the PX4 board series (old and new)

The new PX4 Pixhawk module is an evolvement of the existing FMU and IO modules and completely compatible. The main difference is the target audience: While the FMU and IO stack is super small (the size of an average 8 ch RC receiver) but in some ways almost too densely packed, Pixhawk has more space, more serial ports and more PWM outputs.

As the above picture shows, there are two groups of servo connectors, one main group of 8 outputs which are wired through the backup processor, and an auxiliary group of 6 outputs directly wired to the main processor. The port labeled "RC" can take normal PPM sum or Futaba S.Bus inputs, the port labeled "SB" can read RSSI our output S.Bus to servos. A Spektrum satellite compatible port is on top (labeled SPKT/DSM).

The basic operation is the same, and the software is shared. Inside Pixhawk a FMUv2 and an IOv2 do their duties on a single board (and developers will find that the software will refer to FMUv2 and IOv2)

The main differences between old and new are:

  • 14 PWM outputs vs. 12 PWM (old)
  • All PWM outputs on servo connectors (old: 8 on servo, 4 on DF13)
  • 5 serial ports vs. 4 (with some double functionality, so only 3 in some configurations on old version)
  • 256 KB RAM and 2 MB flash vs 192 KB RAM and 1 MB flash (old)
  • Modernized sensor suite (latest generation)
  • High-power buzzer driver (old: VBAT driven, not as loud)
  • High-power multicolor led (old: only external BlinkM support)
  • Support for panel-mounted USB extension (old: not present)
  • Revised, improved power architecture
  • Better protection on all input / output pins against shorts and over voltage
  • Better sensing of power rails (internal and external, e.g. servo voltage)
  • Support for Spektrum Satellite pairing (needed some manual wiring work in v1, but also software-supported)
  • No more solid state relays on v2 (was not really used)
  • Connectors easier to disconnect in case, as the surrounding plastic helps to place the fingers correctly (more on this in a separate post)
  • Case prevents one-off failure operation of servo connectors
  • The new unit is consirably larger, has the same height, but offers in general more handling convenience.
  • External power supply similar to existing 3DR power brick (every unit comes with a free module)

Both generations offer the same backup / override processor that allows failover to manual if the autopilot fails in fixed wing setups. For software developers the differences are nicely abstracted in the PX4 middleware, and can be sensed / configured at runtime.

Pixhawk is available for pre-order here.

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Comment by Joe on September 1, 2013 at 5:35am

I am bored reading yet another Bill Of Materials BOM.

This is not a receiver which can be mounted anywhere using double sided tape, it requires correct alignment with the frame, it needs mountings tabs or mounting holes,

Comment by Rob_Lefebvre on September 1, 2013 at 5:41am

What is the details on this?  It's not obvious what you're saying.

  • Support for panel-mounted USB extension (old: not present)

I do like the idea of an external panel mount USB port.  But it was technically always possible.  Just buy a panel mount USB jack and a short extension cable.  So I'm not sure what this feature is.

Comment by Lorenz Meier on September 1, 2013 at 6:02am

@Robert: It is possible, but if you look at the length of a normal USB plug it exceeds the available space in most airframes, and your approach will hence only work in really large airframes, exceeding a normal quad or fixed wing size. Its a direct 4-pin DF13 connector, also useful if you want to connect USB to something onboard.

@Joe: If you could let us know *what details* you're interested in, I think we can make sure to cover those as well. The nature of a hardware announcement is to give details on hardware. That it supports all the existing PX4 and APM software was known before.

People actually interested in using it or with a PX4 board in their airframe will appreciate the "Changelog" (as requested in the announcement comments), as it makes much more transparent how they relate and it shows the continuity better than the first announcement post could. The benefit of an upgrade for APM 2.x hardware users is obviously more processing power, this list will help existing PX4 FMU users to judge if / how they would benefit from an upgrade.

Comment by Thomas J Coyle III on September 1, 2013 at 6:09am

Hi All,

I use these Adafruit USB B Female to Micro B Male panel mounts on my rovers and they work very well: http://www.adafruit.com/products/937


TCIII ArduRover2 Developer

Comment by Lorenz Meier on September 1, 2013 at 6:15am

@TCIII Thanks for sharing the link. As mentioned they work great for rovers and helis, but this plug would neither fit into Iris or an Easystar, as the plug and cable (when bending it within its design specs) would not allow to fit it.

Comment by Euan Ramsay on September 1, 2013 at 6:20am

Might be worth writing an article on how to upgrade/migrate to the new platform; I'm keep to take advantage of it, but want to preserve my existing spektrum AR8000/TM1000, gimbal controls etc from the APM. A beginners guide to to PX4/pixhawk, if you will.

Comment by avionics on September 1, 2013 at 6:46am

This looks awesome !!! very nice design, well-done to you guys .

Comment by Hugues on September 1, 2013 at 7:36am

Huumm will I wait christmas or not ? That is the question. I f anyone buys my current 8 rc tiger motors 3110-17 (700Kv), as describer here : http://www.diydrones.com/group/arducopterusergroup/forum/topics/tig...


the  I might get this sooner...

Comment by Crashpilot1000 on September 1, 2013 at 7:40am

What makes the ST sensorset superior to the Invense / Honeywell setup (like also used on Naza etc)?

Comment by Lorenz Meier on September 1, 2013 at 7:46am

I have already commented on the sensor selection in the other thread but basically:

  • The HMC5883 is already manufactured by ST (press release from Honeywell)
  • The MPU6K and HMC5883 are by now 2.5 years old, and the field has progressed since then
  • The resolution of the LSM303D is nominally higher
  • Our tests showed in a head-to-head comparison that the new sensors to perform very well, including presence of strong vibration


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