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

By PX4 [ http://diydrones.com/profile/PX4 ]

DIYDrones.com

September 1, 2013

The new PX4 Pixhawk module [ https://pixhawk.ethz.ch/px4/modules/pixhawk ] is an evolvement of the existing FMU [ https://pixhawk.ethz.ch/px4/modules/px4fmu ] and IO [ https://pixhawk.ethz.ch/px4/modules/px4io ] 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 [ http://store.3drobotics.com/products/3dr-pixhawk ].

4:30am

by Crashpilot1000 [ http://diydrones.com/profile/Crashpilot1000 ]

September 1, 2013

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

7:40am

by Lorenz Meier [ http://diydrones.com/profile/LorenzMeier ]

September 1, 2013

The HMC5883 is already manufactured by ST (press release from Honeywell ] http://www.prnewswire.com/news-releases/honeywell-announces-next-generation-3-axis-compass-chip-that-delivers-low-cost-high-accuracy-positioning-for-handheld-devices-80956102.html ])
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

7:46am

by Stefan Gofferje [ http://diydrones.com/profile/StefanGofferje ]

September 1, 2013

I wonder why the return to the integrated compass system. Wasn't there consent among the developers that the compass should be external and ideally far away from ESCs and motors? Or is this LM-model immune to EMI?

Is it possible to disable the integrated compass?

10:09am

by Chris Anderson [ http://diydrones.com/profile/zlitezlite ]

September 1, 2013

Stefan: It supports both external and internal mags (software switchable). Choice is up to user based on where the autopilot is placed.

10:15am

by Lorenz Meier

September 1, 2013

@Stefan: There is no return here. The internal compass is for free with this sensor setup, so no use not interfacing it. In contrast to APM 2.x hardware the external compass was always auto detected and the system startup will pick the external over the internal one.

If you connect a 3DR GPS with compass and orient the arrow front, you're immediately ready to go. You can also configure different orientations in the PX4 stack, and APM@PX4 has also the option to configure the compass orientation differently, if the arrow is not pointing front/up.

10:16am

by Stefan Gofferje

September 1, 2013

Chris, Lorenz:

Thanks for clearing that up! The automatic detection on startup is very cool! Is the Pixhawk as straightforward as the APM regarding config and firmware updates through mission planner? How about QGroundControl. I understand that QGC is supposed to be the primary GC for the PX4. Is that also valid for the Pixhawk? Is configuration/FW update possible through QGC? I would love that because then I could finally lose that Windows XP VM I am maintaining just for APM planner.

Pixhawk definitely looks like a very good option for my Y6 project.

12:30pm

by Chris Anderson

September 1, 2013

Stefan: we will be releasing new GCS software that works and looks like Mission Planner but is based on the cross-platform QGroundControl architecture.

12:33pm