I plan to build a hexacopter with the Pixhawk flight controller. I was researching it up and found the Pixhawk 2.1 version which comes with a CUBE and EDISON option. Also online on eBay I found a Pixhawk 2.4.8 as well. However, the data available was not comprehensive and I have the following doubts.

1> What is the difference between Pixhawk 2.4.8 and 2.1?
2> Can the Pixhawk 2.1 be paired with a companion processor? I am looking at pairing it with the Raspberry Pi. 
3> Can the Pixhawk 2.1 Edison version be paired with the Raspberry Pi?

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1: "2.1"  Is the latest pixhawk , (with Cube)  , PX4 2.4.8 is the PCB/version of the first Pixhawk (3DR Pixhawk)

2:  no "pairing" involved, yes, just like Pixhawk , Pixhawk 2.1 can be used with companion computer.

3: yes, having the Edison space, does not prevent it from interfacing any other computer.

Hmm, so as I understand

- Pixhawk 2.1 (CUBE) for all my aircraft control, telemetry and mission execution both in manual and autonomous mode.

- A companion Raspberry Pi for gimbal control, datalink, object/pattern detection and other processing.

- The Pixhawk will be be  able to do two way communication with the Raspberry pie for

    - Aircraft data transfer to Raspberry and

    - Mission modification from Raspberry based on datalink feed from user or onboard image processing by Raspberry.

Kindly confirm my understanding is correct. If not please correct with brief explanation.

Arunava,    The Pixhawk1 (2.4.8 and 2.4.9) has a slightly better IMU(lower noise gyros) than the Pixhawk 2.1.      Here is a link to the mRo Robotics autopilot store web page.    It has good descriptions of the autopilots that will allow you to form your own understanding the differences.     The Pixhawk 2.0 is the 3DR version that has the better IMU.  

https://store.mrobotics.io/category-s/113.htm

You can hook the Rasberry Pi up with the Pixhawk 1 via a one the pixhawk serial ports.    Here is a link the the developers page that discusses how:

http://ardupilot.org/dev/docs/raspberry-pi-via-mavlink.html 

Can you please tell me the difference between 2.4.8 and 2.4.9. Also, which is the IMU on 2.1 and that on 2.4.x.

Further the 2.1 advertises itself as triple redundant IMU and double barometer. So does that mean that the 2.1 has two seperate barometer sensors and three seperate 3-axis gyro & accelerometer?


2.4.9 changed some resistor & capacitor values , unless I am mistaken, trivial.

as for 2.1 , yes, more redundancy - but maybe equally important; more different sensors and sampling rates, less chance of aliasing.

The Pixhawk1(2.4.x) uses the MPU6000 IMU, a redundant set of gyros(L3GD20 3-axis 16-bit gyroscope) and accelerometers(ST Micro LSM303D 3-axis 14-bit accelerometer / magnetometer).    The MPU6000 IMU gyro noise(0.005 deg/sec/root(Hz) and sample rates are pretty much the best.   Aliasing is not a problem as the MPU6000 includes anti-aliasing filtering.

- L3GD20 gyro (a very noisy 0.03 deg/sec/root(Hz))
- LSM303D accelerometer / magnetometer
- MPU6000 accelerometer / gyro / magnetometer(0.005 deg/sec/root(Hz))

The Pixhawk2.0(3DR) uses the MPU6000 also.     

From the mRo site:

"This Pixhawk (2.4.9) has a few improvement that never made it to the public, including STM32F427 revision 3 that corrects a bug that limited the Pixhawk to 1MB of flash. Note that most of the original PixHawks do not have rev. 3."

The Pixhawk2.1 uses:

- L3GD20 gyro (a very noisy 0.03 deg/sec/root(Hz))
- LSM303D accelerometer / magnetometer
- MPU9250 accelerometer / gyro / magnetometer(0.01 deg/sec/root(Hz))

The MPU6000 has half the noise of the MPU9250, which makes initial leveling and attitude control better.

The Pixhawk2.1 is an well designed autopilot.    Not sure why the lower performance IMU was used.   Only one MPU9250 IMU is on the isolated IMU board.   The ICM20600 IMU could have been used and it is slightly better than the MPU6000.

Here is a link to the Pixhawk2.1 specification:

http://www.hex.aero/wp-content/uploads/2016/07/DRS_Pixhawk-2-17th-m...

cuav sell his own version for 140eur

So, which one would be preferable for building a hexacopter with high stability?

you wont see difference between Pixhawk or Pixhawk2 performance, you should rather focus on buying properly assembled and high-quality manufactured hardware from reputable vendor. 

For high stability you want the autopilot with the lower noise IMU gyros.    The Pixhawk 1 with the lower noise MPU6000 IMU gyros is a better autopilot for hexacopter stability.    The Pixhawk 1 uses the same processor as the Pixhawk 2.1 and same clock frequency.

Hobbyking has a pretty good deal on the Pixhawk1 v2.4.8,    mRo has perhaps a little higher quality in the Pixhawk1  v2.4.9.

Andre,  what do you mean by "PCB/version"?  They all have PCBs.

Who came up with this crazy numbering scheme?  US Robotics?  I'm a former embedded system hardware developer who changed careers and now develops embedded firmware.   This numbering is not industry standard.  How can a newer and more advanced pixhawk (the cube) have a number (2.1) less than the previous pixhawk (pixhawk 1) which seems to be numbered as 2.6.x or 2.4.x ?

Industry standard numbering is as follows:

x.y.z

where x = major version, y = minor version z = manufacturing version

x and y: Major vs. minor (subjective) refer to form, fit or functional changes such as adding new features.  These are always "visible" to the customer. 

The z or what I am calling the manufacturing version, usually refers to cosmetic changes such as cuts and jumpers that fix errors on the schematic, bugs, part changes such as manufacturing finds a cheaper substitute part, etc.

The same versioning system is used in software/firmware as well.  In that case, the third digit is usually reserved for bug fixes or other changes that the customer will never need to know about.



Andre K. said:

1: "2.1"  Is the latest pixhawk , (with Cube)  , PX4 2.4.8 is the PCB/version of the first Pixhawk (3DR Pixhawk)

2:  no "pairing" involved, yes, just like Pixhawk , Pixhawk 2.1 can be used with companion computer.

3: yes, having the Edison space, does not prevent it from interfacing any other computer.

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