In my last post I showed a Flip32 flight controller talking to a PX4Flow unit using the I^2C protocol.  Once that was working, I wanted to mount the PX4Flow to a vehicle and make a more permanent cable connection.

For the mount, I used Tinkercad to design a simple rectangular plate with four recessed screw holes, plus a small rectangular hole to pass the I^2C cable through.  Four M3 nylon machine screws and standoffs, both 5mm size, fit snugly into the holes, after which I mounted the plate permanently on the rear  bottom plate of my 250mm H-quad using E6000 adhesive.  

To make the cable, I soldered one end of the four-position cable from 3R to a four-pin jumper cable from Sparkfun.  To keep the color-coding sensible, I covered the red jumper wire with black heat-shrink tubing, making it the ground (leftmost) of the four I^2C pins on the Flip32.  Then the orange wire was +5V, the yellow SCL, and the green SDA:

Once the PX4Flow unit was mounted and wired, I found that the vehicle's legs were too short.  So I designed and printed some extra-long legs, allowing the unit plenty of ground clearance:

My ultimate goal is to modify the Flip32's Baseflight firmware so it uses the sonar and optical-flow readings from the PX4Flow to perform altitude- and position-hold.  Before doing that, I plan to collect in-flight data from the PX4Flow, by attaching a Bluesmirf modem to the Flip32's UART pins and sending a new MSP message from the Flip32 to a Python program on my laptop.

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Comment by Stephen Zidek on December 8, 2015 at 11:11am

Nice work Simon!  I do have a question.  The wiki says that the PX4Flow's sonar is insufficient.  Have you found this to be the case?


Comment by Simon D. Levy on December 8, 2015 at 11:20am

Thanks, Stephen!  The PX4Flow sonar is apparently insufficient for using with the Ardupilot firmware, but I'm writing my own addition to the Baseflight firmware and will be using my own EKF if necessary.  Because the existing Baseflight firmware works pretty well with a cheap sonar unit, I'm optimistic that I can get it to work with the one on the PX4Flow.  I do have  a LidarLite unit and other MaxBotix sonars as a backup, but I want to try the built-in sonar first.

Comment by Charles Blouin on December 8, 2015 at 4:08pm

I worked with the sonar for altitude control before, and we needed to do some sensor fusion with the accelerometer to obtain a good altitude hold.

Comment by Charles Blouin on December 8, 2015 at 4:22pm

PS: *I worked with the PX4FLOW sonar

Comment by Simon D. Levy on December 8, 2015 at 5:09pm

Thanks, Charles, I agree.  This is why I wroteTinyEKF, anticipating such a need.

Comment by Guillermo Ortiz on December 10, 2015 at 9:16am

I start my Masters of Science in Unmanned Systems at Embry-Riddle Aeronautical University Jan 2016, I am immensely grateful to the Veterans Administration for their sponsorship!

Comment by on December 10, 2015 at 11:19am

Nice work :-)

Comment by B on January 14, 2016 at 8:04am

You're getting so good with the CAD and 3D printing I don't have to do it for you anymore. Great work Simon!


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