It's been a while since I've posted an update on the progress of the AutoQuad flight controller.  The event that we've all been waiting for has arrived with ST Micro's announcement and subsequent release of their STM32F4 product line.  As expected, the micro-controller is pin for pin compatible with their STM32F2 series which the AQ v6.1 hardware was designed for.  This meant it was a drop-in replacement.  The most important new feature of the chip is the implementation of ARM's Cortex M4 core with a hardware FPU!  This means that we can now do floating point operations in a single clock cycle.  All forms of add / subtract / multiply / integer conversion, etc are single clock cycle instructions with the divide and square root instructions taking 14 cycles.  This is a significant step forward for math hungry applications like AutoQuad.

As soon as I could get my hands on one (around November I think) I had it on a board working to port my ground Unscented Kalman Filter code to fit into the 168MHz MCU.  With some optimizations, it ended up fitting with processing room to spare.  The current version leaves ~40% idle time during flight.  The filter is interesting because it brings all of the important estimated states and observations under a single mathematical model.  This means that each observation can influence any number of state estimates if there is determined to be co-variance between them.  The theoretical performance improvements over my old fixed gain techniques is high.  17 states and 16 process noise terms are estimated at 200Hz observed by 13 sensor measurements.

A benefit to using such a filter onboard is that it can adapt to changing variance of sensors and measurements on the fly.  This removes the need to do ground based flight calibration simulations which was a drawback to the original fixed gain methods.  Once you have a calibrated IMU, it can provide accurate state estimates "out of the box."  While this is nice, the biggest improvement is the accuracy of the state estimates it can produce.  States like 3D accelerometer bias and 3D rate gyro bias are critical to accurate attitude estimates which is the only way that you can propagate acceleration measurements through velocity and position estimates with any kind of accuracy.

Other than the upgrade of the MCU, the hardware is mostly unchanged from the original v6.1 layout.  However, there have been a lot of new features added to the firmware since last year.  What I call DVH (dynamic velocity hold) allows the pilot to control the craft's velocity in 3 dimensions while AQ handles everything else.  Let go of the sticks and the machine holds position.  AQ now speaks mavlink so it can be configured and controlled from any ground station that supports the protocol.  A comprehensive parameter set has been established that allows configuration of almost all aspects of operation.  Gimbal support and expanded mission capabilities have been added.  1-wire support for pre and post flight communications with ESC32.  Too many more to list here.

With the help of Max Levine I created this video to demonstrate the autonomous mission capabilities of the current firmware (version 6.6):

If you use the uBlox LEA-6T as the onboard GPS module, AQ can record raw satellite observations to its uSD card along with the normal flight log.  With this data and data from a local base station, you can use post RTK to get extremely accurate position and velocity estimates (~ centimeter accuracy.)  In fact, I use the RTK velocity estimates as an absolute data point in scoring the filter's performance in the ground simulations used to tune the variance and noise parameters used by the UKF.  Future work might include onboard RTK calculations using a linux based application processor mounted on a daughter board.  This would bring the system's performance to an entirely new level.

Here is what the actual flight path looked like of the flight shown in the above video using post processed RTK:

I need to thank the small group of people who have worked very hard to test, write utility software and interfaces, create documentation and generally improve the AQ  platform.  It is still very far from a finished, polished flight controller, but it has come a long way because of their help.

As with ESC32, I have decided to release the AutoQuad FC firmware under an open source license.  It can be found at:

I would also like to invite anyone interested to participate in a public beta test of the system.   Sensor calibration, setup and configuration is still a lengthy and sometimes tedious process so I would discourage anyone who thinks they can bolt the board to a frame and start flying as that is not at all what you should expect.  I have authorized manufacture and sale by ViaCopter and Flyduino who are taking orders in a few days.

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Comment by Vincent Mees on July 3, 2012 at 3:11am

Or is it compatible with for example MP for arducopter because it also uses Mavlink..

Comment by Norbert Machinek on July 3, 2012 at 3:14am

The new AutoQuad site waits for being read. We have an almost ready wiki there, flight and instruction videos, a download section at and forum at

We use the QGroundControl with an AutoQuad Main Widget for flashing, setting up the copter and waypoint navigation.
For an easy handling on the flight field we offer a specially tailored Android version.
You can program your waypoints by clicking/touching a Google map.

Comment by Ita G on July 3, 2012 at 3:20am

That's just great, Bill!
Keep pushing the envelope, you're helping us all :-)

Comment by Vincent Mees on July 3, 2012 at 4:01am

Very promising!!

Comment by Aerhead on July 3, 2012 at 5:00am

For six years I've been looking for a autopilot that would have the functionality that AQ autopilot appears to have attained. It's interesting that it will be released just a day ahead of the July 4 "Independence day".  I believe that this autopilot and it's open software has the potential to change way people think about how things fly. No longer will an aircraft have to be blown around be wind.  

This octo I built just to get the idea out of my head and into hardware.  It uses two quad flight controller that fight each other to keep the craft level.

This autopilot with additional channel mixing could produce a craft that could pick fruit in a breeze.  It's just fun to see all the possibilities.

Comment by Héctor García de Marina on July 3, 2012 at 5:09am

By the way, will be the hardware schematics open source as well?

Comment by Mike on July 3, 2012 at 5:21am

Nice work Bill. What antenna are you using with the GPS to get RTK lock?



Comment by Michael Zaffuto on July 3, 2012 at 5:59am

Excellent job Bill..truly state of the art.

sensore - finis de vita?

Comment by Norbert Machinek on July 3, 2012 at 6:10am

@ Vincent: yes, you can connect it to the MegaPlanner with MavLink 1.0 as well. But since the underlying firmware and commands differ much, you can only use it for HUD and GPS position display - not for the setup which is completely different. 

@ Hector: the firmware/software will be open source, the hardware will be not.

@ Mike: the package will come with a big active ceramic antenna:

Comment by Jeroen van de Mortel on July 3, 2012 at 6:37am

Very nice again, very high quality. Great job Bill.


What are you going to do about the EOL status of the analog invensense sensors ? Or are using different sensors than in version 5.6 (could nog find it)? Only Analog Devices produces analog sensors, but they are expensive. And ST also has only digital ones.


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