The uNode


A distributed and scalable autopilot architecture is attractive to me due to space and sensor positioning demands on my airframes.  The existing range of autopilots simply doesn't fit.  The uNode (microNode) is the result of my desperate attempts to fix this.  uNode is a very cutdown version of Pixhawk with a little bit of AUAV-X2 added.


Board contents are:

  • STM32F427 Processor (as per pixhawk)
  • 64Mbit onboard flash - no sdcard
  • 4.5V to 10V input power supply or power from USB.
  • No USB connector, only 0.1" holes
  • MAX21100 6dof sensor - an experiment and about the only sensor I have space for.
  • No I/O buffers.  ESD and EMI protection on everything.
  • Power for GPS module
  • SRAM Battery backup
  • Pinouts for
    • 2x I2C
    • SPI
    • 3x UART
    • 2x CAN with transceiver onboard
    • 8x servo outputs
    • PPM input
    • SBUS or Spektrum module input.

Total manufacturing cost in volume may be ~$25.

These boards are designed to fit into the servo hatch of a wing.  They have about the same area as a slim wing servo.  There is no USB connector because there is absolutely no space for one.  There is no sdcard because it is not accessible.  Some other potential uses:

  • As a CAN connected failproof board
  • Failproof remote servo expander
  • Remote sensor interface - I2C sensors over long wires without interference.
  • A backup, get you home autopilot.  Just add GPS module.

The board uses the same processor as the pixhawk so that the same OS and software is used.  You pick whatever you need to run in what node location.  The dual CAN can then be used to setup a robust network to transport the data between nodes.  The PX4 firmware is structured to be very suitable for this.

The prototype hardware functions well.  The onboard flash works and I have had bi-direction file transfer over mavlink-ftp working.  I had it working...  The PX4 codebase has taken another leap forward, broken my branch and I somehow need to catch up again.

That's all for now until I manage to make it do something useful.

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  • ahh i see you have tried a few :) yes its not a cheap thing to do ,the tools of the field is the expensive part for sure , been designing boards for a few multirotor designers over the last two years now but most the tools i had from earlier unrelated rc work and i cant really include them in the startup costs for new products , so sometimes i forget what some experience when doing so, your right about the cloners, I have a few now gone that route

  • @Charles,  I could but I won't.  The PX4 original is in eagle.  Re-using the existing open source design and contributing back to it is easily worth $150.

    I tried kicad.  The libraries are simply awful.  Overall it comes across as the  brainchild of a true linux geek.

    Designspark has awesome libraries but the gui is painful.

    I also have eagle scripts to generate routing output for my 3d printer pcb routing setup.  I have been using the free version for so long I figure I owe them some $.  I don't regret this purchase for a moment.

    Then add:

    Debug tools: $250+ after various experiments

    Digital current limited power supply: $150 (saved the board several times, worth the money)

    Parts: ~$300 - I didn't look too close at the actual cost.

    THIS IS AN EXPENSIVE BUSINESS.  Have respect for anyone prototyping anything. It is costing way more than you think.

    Do I think I will get my money back?  No!  If it is popular enough it will be copied.  I someone thinks they can make money from this design then I invite them to do so.

  • you could use numerous FREE unrestricted design software packages even for commercial use like..

    DESIGNSPARK (Free for commercial or non-commercial use, no limitations or licensing)

    kikad -

  • @Charles,  I did do the board design myself. It's the only way to get what I want and to properly review the layout.  That's an extra $150 for the private eagle license.  If I ever want to sell these things then that will be an extra $500.

    As I said earlier in this thread, the local tax man hates people making innovations that lead to enough wealth to put food on the table.  That would be unfair to people who have no ideas of their own.

    @Bill,  It's been a few years since I did a PCB design. Like riding a bicycle... a very rusty bicycle with flat tyres and seized bearings.

  • Developer
    Great work Mr Coleman. Also good to see new options, I'm sure you have learnt lots :-)
  • I like the size, why did you pay so high for the development did you not do the design yourself? or was it done by a board designer based on your needs? just wondering why you didn't fab a small batch through oshpark and populate yourself for the test run

  • @Ye, MAX21105 is more accurate than MAX21100 and cheaper. Availability was just a little too late for this project.
    It is cheaper since it does not have the motion merging engine that we can't use anyway. The interrupt mechanisms are simpler and I have not yet worked out if that is significant or not.

  • Good job! MAX21100 is very accurate based on its datasheet. Hope to get your test results soon!

  • @Roberto, I forgot to say that the debug connector is too deep to be mounted when fitted in the aircraft.  Anything but through hole connections is a no go. 

  • @Bill,  Not much market at all so far. I did this to make sure that I have something that fit inside the aircraft.

    I don't plan to sell them since I will get into arguments with the local tax man and he will take most of my money away.  I might get the place that manufactured the prototypes to sell to a distributor.

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