Sunday, August 28, 2016

Probe nose design ongoing

Currently working on the design of the probe nose -- a critical part that we hope to 3D print, perhaps with an agency that uses Carbon3D. Here are a couple of views:

We now have a shared Google Drive folder for things that don't belong in the GitHub repo, like CAD files, Google documents and the like. To start with, you can download the CAD files for the above file from there; just navigate the folder hierarchy in the obvious way. :) This is a link for access to the Drive folder:

Stay tuned for more!

Friday, August 26, 2016

Airball, and other EAA prize finalists, in the news!

The EAA just recently posted an article by Beth Stanton about Airball and the other four EAA Founders Innovation Prize finalists! Go check it out!

Tuesday, August 23, 2016

Components coming in!

I got a sweet new Lenovo Thinkpad P50s to use with the EAA's free SolidWorks member benefit. The result is as you see, starting to design the probe nose:

It turns out the Arduino UART uses TTL rather than RS-232 levels, so testing with a computer with a hardware DB9 connector is an exercise in futility. Who knew? :) So we have a new FTDI USB/serial adapter with bare pinouts we can experiment with:

Finally, I got some Tygon tubing and a bunch of the cutest and littlest barbed tubing connectors imaginable. These have a 1/16" diameter barbed fitting, and a 10-32 thread on the other side. The idea is that these would fit into tapped holes in the 3D-printed polymer probe nose, and connect on the other side to similar fittings built into the pressure sensor chips:

Sunday, August 14, 2016

Arduino beginnings

The Airball probe will consist of:
  • 4 Honeywell TruStability "HSC" (high accuracy) sensors --
    • 3 differential sensors reading ΔP for α, β, and the dynamic pressure Q;
    • 1 absolute sensor reading the static pressure
  • 1 Honeywell air temperature probe
My hope is to be able to get true airspeed out of the probe, since that only requires adding one more pressure sensor and the temperature sensor. Might as well.

The pressure sensors have an I2C interface. The temperature sensors are analog.

The plan is to read these out by an Arduino, using the built-in I2C interface for the pressure sensors and the built-in 12-bit ADC for the temperature. The resulting data sentences will be sent out over an XBee radio to the display unit.

I got myself an Arduino starter pack from Adafruit. Today, I convinced myself I can get my Arduino to read analog and I2C bus values from a potentiometer and a proximity sensor, respectively. Next is to send in a quote for the sensors (it's complicated since you have to encode your desired I2C addresses in the part numbers...).

Thursday, August 4, 2016

Next steps

To get Airball into the hands of real pilots, we need to build something operationally useable. Sort of a minimum viable product. We can continue messing around with smart phones and slurping data from whatever Dynon units we can, but that's not widely installable or applicable.

Our job at this point is to build a probe and a display unit, which connect to each other wirelessly. This should allow installation in any aircraft -- certified or Experimental -- just like clipping a GoPro camera to a strut.

Probe design

As described in our paper, the probe has a large radius nose so that we don't need to mess around with calibration. Taking an idea from the 2nd-place winner of the EAA competition, it can be powered by a little windmill, so it's self-contained and never needs battery charging or wires.

The sensors we plan to use are Honeywell TruStability, the better versions of which boast accuracies of 1% of full scale. These provide an I2C interface.

The probe will emit data as 7-bit ASCII "sentences" separated by newlines, consisting of human readable pressure measurements in engineering units. This makes the protocol debuggable yet reasonably compact. It would look something like:


where the XX is a checksum and the newline ends each "sentence." This is very similar to NMEA sentences emitted by GPS receivers.

We may consider adding a measurement of barometric pressure, and a temperature probe, allowing us to infer true airspeed. We have an idea for adding TAS to the Airball display for even better situational awareness.

For the radio link to the display, we expect we'll probably use a point-to-point XBee. This will ensure that we do not interfere with Wi-Fi or Bluetooth devices used by the pilot elsewhere. It should also remove the need to "pair" radios -- each probe and display will have a hexadecimal code baked in (e.g. via coded rotary switches), so the link is basically a simple "wireless wire."

The sensor readings will be scanned by an Arduino, converted to engineering units, and then pumped onto the serial link. That's all the processing in the probe.

Our hope is that the innards of the probe, and the radio link, will be simple enough that, as soon as the windmill starts turning, the probe will produce data, which will be immediately visible on the receiving end. So it would be almost like airspeed "comes alive" on the runway, within a matter of milliseconds, without waiting for devices to pair with each other or DHCP handshakes over Wi-Fi or any of that.

Display design

The display will be an embedded Android board (probably a BeagleBone Black) running a stock Android that's been tricked up to launch our app on startup. It will contain a paired XBee radio to get data from the probe.

It will have a high brightness (at least 1000 nit) LCD panel. The high brightness display is really the main reason why we're choosing not to go with a regular smart phone.

We plan to add a single pushbutton and rotary encoder knob for all functions including modifying the display parameters (limit AoA values, the position of the annotations for various "interesting" values of AoA, scaling of the ball to airspeed, etc.):
  • Long-press (e.g. 5 seconds) to get into Setup mode. This brings up the currently editable parameter on the screen.
  • Rotate to modify the value of the parameter.
  • Short-press to cycle to the next parameter.
  • Long-press to exit Setup mode. If no activity for a while (say 30 seconds), Setup mode ends automatically.
  • Outside Setup mode, the knob acts as a brightness control.
Power can be provided by a simple 12V "cigarette lighter" cable.

Tuesday, August 2, 2016

Welcome to Airball!

This blog is intended to chronicle the progress of the Airball project.

What Airball project, you ask? Well, we have a novel way to display airdata to help pilots fly airplanes more safely, and we just won a generous award from the Experimental Aircraft Association [press release].

We hope to get this system into the hands of pilots and flight students as soon as we can, to get feedback on how it helps and how it can be improved.

Our vision is outlined in our submission to the EAA [PDF link]. If you are interested in Airball, this is a good place to start -- we have made it easy to read in chunks.

There are not really any affordable aircraft systems that gather the airdata we need for Airball, so our first job is going to be to build an inexpensive airdata probe that can be clipped to the outside of any airplane like an action camera, and which sends data wirelessly to a display unit. Stay tuned for our adventures!