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Dueling Raspberry Pi drone autopilots ship in Q1

Jan 5, 2016 — by Eric Brown — 3,545 views

Erle Robotics unveiled a Dronecode-ready “PXFmini” drone autopilot for the Raspberry Pi, and Emlid updated its Pi autopilot to a HAT-ready “Navio2.”

In 2014, Emlid launched a Navio drone autopilot shield for the Raspberry Pi. Last month, the company unveiled a Navio2 update with HAT compatibility, and now Spanish drone firm Erle Robotics has launched a competitor called the PXFmini. The shield works with any Raspberry Pi, but is optimized for the Raspberry Pi Zero.



Navio2 (left) and PXFmini autopilots, each paired with a Raspberry Pi 2
(click images to enlarge)

 

Erle Robotics PXFmini

We’ll begin with the PXFmini, which launched Dec. 28, and is due to ship in February starting at 69 Euros ($74). The PXFmini shield supports The Linux Foundation’s open source Dronecode flight stack, based on open source APM and Pixhawk standards. Dronecode is gaining support from companies including Qualcomm (Snapdragon Flight) and Parrot, which just announced its first fixed-wing drone, called the Disco.


Erle-Copter
Ubuntu Core Special Edition

In 2014, Erle Robotics introduced the first open-spec Linux-based drones running a Linux version of 3DR’s previously Arduino only-based APM (ArduPilot Mega) drone autopilot platform. The Erle-Copter and other drones built around its BeagleBone-based Erle-Brain autopilot, which runs Ubuntu or Snappy Ubuntu Core, shipped before 3DR’s similarly Linux/APM Solo. This was also before the re-launch of APM as a Linux-ready Dronecode project.

In September of 2015, Erle Robotics launched a six-legged Erle-Spider robot built around a new Erle-Brain 2 autopilot controller that moved from the BeagleBone to the Raspberry Pi 2. This experience no doubt helped in the development of the PXFmini, which is not based on the Pi, but is designed to work with it as an add-on.



Rendering of the PXFmini (without the Pi)
(click image to enlarge)

The PXFmini can work with any Pi, as well as Pi clones including the Orange Pi and Odroid-C1-C1+ SBCs. However, its connectors are optimized for integration with the $5 Raspberry Pi Zero. The shield measures 71 x 31mm, just slightly larger than the 65 x 30mm Pi Zero. It weighs 15 grams, so combined with the 9-gram Zero, you’re looking at an onboard drone computer weighing only 24 grams, the total weight of the Navio2 alone.


PXFmini in real life
(click image to enlarge)

The PXFmini is equipped with dual I2C ports, a UART port, 8x PWM output channels, and a PPMSUM radio input borrowed from Pixhawk designs. Other features include a 9-axis inertial measurement unit (IMU) — an MPU9250 chip — as well as a digital barometer (MS5611) and an ADC for voltage measurements. Instead of using DF13 connectors, the device uses more durable, Dronecode-approved JST GH connectors, as well as DF13-to-JST GH converters.



PXFmini explained on YouTube

 
Further information on the Erle PXFmini

The Erle Robotics PXFmini is available now starting at 69 Euros ($74). The price expands to 149 Euros ($160) with the addition of a 25-Euro power module and a 55-Euro UBlox Neo 7M GPS radio. MicroSD cards with OS images start at 10 Euros, and four JST GH and DF13-to-JST cables are available at 4-Euros each. Shipments are set for February.

 

Emlid Navio2

Emlid’s Navio2 features are a bit higher end than the PXFmini, but at a slightly higher price. The device is APM compatible, and is recommended for use with the Raspberry Pi 2, but it can work with the Zero and other Pi boards. The Navio2 is said to support flight modes including manual, stabilize, follow-me, and auto.



Navio2 without the Pi (left) and stacked with the Pi
(click images to enlarge)

Like the interim Navio+ model that followed the original Indiegogo funded Navio, the Navio2 adopts Raspberry Pi HAT (Hardware Attached on Top) technology. HAT enables the Pi to automatically configure its GPIO signals and drivers for use with external devices. The Navio2 is the first HAT device to utilize the Pi’s AUX SPI controller, says Emlid. By using two SPI controllers, sensors can be distributed more efficiently, says the company.

The 65 x 55mm Navio2 is a bit larger than the PXFmini, and at 24 grams, is considerably heavier. Compared to the earlier models, the Navio2 adds a second IMU chip for redundancy and also to “improve flight experience,” says Emlid. Like the PXFmini, it has a MS5611 digital barometer, the performance of which is improved by leaving the device as the only sensor on the I2C bus, claims the company.



Navio2 detail view
(click image to enlarge)

Whereas PWM was previously generated with a discrete PCA9685 chip, Emlid now uses an MCU, which allows the device to set frequencies for output channels by groups. instead of using DMA, PPMSBUS decoding is also now handled by an MCU, referred to as the RC I/O coprocessor, and provides 14 PWM output channels with variable frequencies. This is said to offload the processing burden from the Raspberry Pi. Meanwhile, ADC channels are now said to be more easily accessible via a DF13 port.

The Navio2 adds overvoltage and overcurrent protection circuitry on the power module port, and it continues the Navio+ power supply enhancement of a “triple ideal diode or-ing scheme,” says Emlid. The device ships with a U-blox M8N locational chip with GPS, Glonass, and Beidou support. APM supports MAVLink communication with a wide variety of multi-platform GCS choices, and can send telemetry over WiFi, LTE, Bluetooth, and other radios.

On the firmware front, PWM, ADC, SBUS, and PPM are now integrated in Linux sysfs, “allowing for easy access from any programming language,” says the company. Open-source drivers and detailed tutorials are available both in C++ and Python. The site offers extensive documentation, as well as forums and support, but we saw no evidence of schematics or claims for open specs, as with the PXFmini.




Navio2 explained on YouTube

 
Further information on the Emlid Navio2

The Emlid Navio2 is available starting at $168, with shipments starting in mid-January, but it’s currently listed as being on backorder. Options include a $12 GPS/GNSS antenna MCX, a $9 wire pack, and a $16 power module, which together would bring the total to $205.
 

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