The Challenge of AHRS and the AHRS Challenge


The Challenge of AHRS and the AHRS Challenge

$4,000 Bounty For A Working AHRS Software Implementation

As most of you know, we’re working on a hardware add-on for FlightBox that will include AHRS – the sensors and software necessary to drive a virtual attitude indicator or provide attitude data to a synthetic vision system. We’ve made good progress on this. Our hardware engineer has selected components and is currently working on the board design. What may not seem obvious is that the hardware is the easy part. Software is where the real challenge begins.

Attitude_Director_Indicator.svgIf you’ve ever played with a motion-sensitive game on a smartphone that may seem counterintuitive. A $100 Android phone can easily determine attitude, right? Well, yes – in some situations. It’s easy to accurately determine attitude when standing still or moving at a steady pace. It’s far more complicated when you take into account fixed-wing flight dynamics.

There are several products on the market today that claim to provide backup attitude, and they appear to do – as long as you’re flying straight and level. Drop into a 30° bank and the screen will show it – for a few seconds. But hold the turn for a few seconds and you’ll notice something disturbing: the display starts to level out. After another few seconds the display shows straight and level again – while you’re still turning. Huh?

It turns out that without some very clever software, the hardware sensors fall victim to the same effect that makes your inner ear such a bad attitude indicator – centrifugal force. In straight and level flight, your ear and the inertial sensors in the phone both detect one acceleration, that of gravity. When you’re turning, you are subject to two accelerations: gravity and the “false gravity” of centrifugal force. In VFR your brain compensates for this using your view of the horizon to override what your inner ear thinks is happening. To accurately display attitude the AHRS system needs something similar – a means of determining what sensory inputs it should ignore.

Many, perhaps most, off the shelf IMUs (inertial measurement units) – the core sensors of an AHRS – are built for use in cell phones or quadcopter drones. Neither of these are subjected to fixed wing flight dynamics. To build a real AHRS, the data from the IMU must be filtered to eliminate noise and must have the inertial (centrifugal) vector factored out of the readings. This is the real challenge of AHRS. Without this, you don’t have an AHRS – you have a toy.

Fortunately, there are people out there who are very good at the kinds of mathematics required and who could create a set of algorithms that combines data from an IMU and a GPS to provide a realistic attitude solution. Unfortunately, I am not one of those people. Thus the Open Source AHRS challenge:

Open Flight Solutions in partnership with Aerovie, Hilton Software, and DroidEFB is offering a bounty of $4,000 to the first developer or team of developers who can provide an open source AHRS implementation that can successfully return an accurate and timely orientation based on raw IMU (3 axis accelerometer, magnetometer, and gyroscope) and GPS data. Please see “The Rules” for details on the requirements and terms.

If you are a developer and you think you might be able to solve this, please jump in. If you know any developers who might be interested, please pass this along. We’re know that this problem can be solved in a way that makes GA safer and more affordable.

UPDATE: We’ve decided to extend the challenge through July 15, 2016.

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8 Comments so far

JerryPosted on  12:35 pm - May 24, 2016

Would rather see an ADS-B out solution, preferably a ” one box solution”.

    ssokolPosted on  1:10 pm - May 24, 2016

    You’re not alone. Unfortunately, the FAA certification process costs a lot more than I have to spend. I’ve been told to expect at least a year and at least $500,000 in costs before we could sell the first unit. A bit too rich for me at this point.

bobPosted on  4:22 pm - May 28, 2016

if you are able to come up with a working adsb out i think it could legally be used in homebuilts. if that is correct perhaps that would be enough market to make developing an out capability worthwhile. hope so.

just having your existing product is a blessing. thanx.

for either ahrs or adsb out, will it be retrofittable to existing units? if yes, i think i know what santa should bring me this year!

pardon strange typing. just had rotator cuff surgery, am typing one handed lefty. sigh. can’t fly for now, either. sigh, again.

Phillip HartigPosted on  6:52 pm - May 30, 2016

I am curios as to how your contest is going? I’ve built my own stratux and upgraded to AHRS only to be thwarted by foreflight. Will the winner of your contest be able to solve this problem? If so, what will it cost? Thanks phill

GregPosted on  2:16 am - Jun 7, 2016

Not sure if this is relevant but I have been playing with an open source drone control board with all onboard hardware that may accomplish what you need it to. It is called Pixhawk. Just google Pixhawk and 3d robotics.

MatteoPosted on  11:27 am - Jun 24, 2016

I would say that the AHRS quality is to be defined a priori for this challenge to have some action. Depending on the level of performance expected, the price for HW and SW will easily go up to some 1000s $. There are already on the market some AHRS modules sold for aerospace, you may see if those suffice for you cost/performance needs.

Tom CountsPosted on  5:12 pm - Jul 9, 2016

I ran across this board:
It sells for $75. Apparently it has on-board firmware and can interface with the Raspberry Pi. Looks like the advantage is the math is already done. It has the filters etc. built in. It is also configurable. The youtube video showing it’s resistance to centripetal acceleration is impressive. Is this one that Stratux could support or at least look into? Thanks

AlanPosted on  3:44 pm - Sep 8, 2016

Contact Talos Aviation Greece …they seem o have done it !

I have brilliant AHRS on my S7Edge

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