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Dec 22, 2010, 10:15 AM
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FreeFlightIMU/FreeIMU - libre digital IMUīs

Edit: 24/8-2011

OK, lots of new stuff has happened since I started this. So here is a short recap:

I started out with the idea to make a all-in-one arduino board designed for RC flight and personal UAVīs. The idea grew from the Multiwiicopter, and a desire to replace hacked Motion plus/Nunchuks/arduino/wires and shields with a single board that could hold all the necessary components and be cheap to manufacture, and work for all the different arduino-based FC projects. And available as open hardware for anyone to make!

It very soon changed direction into evolving a digital IMU - FreeFlight IMU. The first version was the 1.1 and only 20 was made of those. It carried the ITG3200, BMA180, HMC5843 and BMP085 sensors.

During the prototype phase it was announced that Honeywell would replace HMC5843 with HMC5883L. And this spawned the first production version, the 1.22l, designed around the HMC5883L. A lot of effort was put into sourcing HMC5883L as it was unobtanium for a while, but with the help of the community the first prototypes rolled out from the factory in the beginning of April. The later batch of totally 100 units was sold out, almost immediately. I did have some issues with the magnetometer, but eventually all was solved and the FF IMU 1.22L has proven to be a good performer in Multiwii, Aeroquad and Ardupirates platforms.

About this time all hell broke loose. It seems people got inspired and all of the sudden everyone seemed to make IMUīs. We have seen several versions come out and be offered for sale here. I always wanted to see this driven forward by the community and be available as open hardware, so people could build it themselves, but not one single of the maybe 5 new IMUs and FCīs that came to market was ever offered up as open hardware

One guy did stand out right from the beginning - Fabio Varesano with his FreeIMU, which is a true open hardware initiative and driven forward by his personal and professional passion for motion-sensing and human interaction. Fabio started working with motion-sensing and IMU design long before I did. His version used another accel and there was no barometer, bit otherwise they were very similar in function

Long story short: Fabio has agreed to take over with FreeIMU, which will become the new "standard". He will take care of design and development in the future - I am sure this will mean higher speed of development and a constantly improving hardware, that also can be used outside the RC world!

Fabio has designed 2 new versions of FreeIMU that will be available very soon, and is intended to replace the FF IMU. The FreeIMU 0.3.5 will be available in two versions with different barometers. The MS version carries the MS5611 pressure sensor, and the BMP version uses the BMP085 pressure sensor! Otherwise they use the same sensors as FreeFlight IMU 1.22L: ITG3200, BMA180 and HMC5883L.

MS version will be available from late august, and BMP version will be available primo september.

First demo vid:
FreeFlight IMU Demonstration (2 min 22 sec)

Flight vids by Warthox:

Early one:
(3 min 48 sec)

Newer one:
(4 min 34 sec)

Multiwii 1.8 and FreeIMU 0.3.5MS:
(5 min 36 sec)

Early mag test:
FreeFlight IMU Compass test (1 min 4 sec)

Early stable test:
FFIMU and Multiwii stable test.mp4 (2 min 20 sec)
Last edited by JussiH; Aug 27, 2011 at 10:48 AM.
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Dec 22, 2010, 10:23 AM
working on a DIY Mini Quad!
Edwardo5000's Avatar
I would like a replacement for the WMP!

Dec 22, 2010, 10:38 AM
Registered User
I would like a replacement for the WMP!
Me too,i second that....

This MultiWii is mature enough for a complete board change, will be nice to design a board that doesn't use breakout board. All discrete and related sensors will be surface mounted on this board.

Dec 22, 2010, 10:44 AM
Thanks for the Fish
With the multitude of clones posing wiring nightmares for those new to the hobby, having an option of a different board with 6DOF would be ideal. Check out some of the Sparkfun offerings.

How are you coming with your first gen of boards? Did you redesign to be compatible with one of the other ACC?
Dec 22, 2010, 10:53 AM
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Kadath's Avatar
Personally I think that the idea of keeping the microcontroller and sensors on separate boards is preferable. Sensors technology evolves much more rapidly than uC. Having a solid uC base board means that the code base can be stable and people can experiment with all kind of sensor boards as extensions.

For the uC side, the ArduPilot Mega seems do have already done everything correctly (except for the price :

What could be done is create a board similar to a Teensy++ but with connectors for a MultiWii application. Then a 2nd sensors board that could plug into the base one in a piggy back fashion.

Just food for thought, there are many many options... Good luck with your project
Dec 22, 2010, 10:53 AM
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rimshotcopter's Avatar
One of the things that I believe is greatly overlooked is, the WM+ has Analog Gyros and an internal ADC. So this makes things somewhat complicated because there are three steps to getting the data into the Arduino. Analog - Digital conversion - I2C. I would suggest making the breakout board compatible with analog devices. I am presently testing some analog devices with the Alex's MultiWii and my preliminary results looks very promising. Right now, I am going a Cycle Time of about 2000 with Gyros only and about 4000 with the Accelerator. I have not flight tested this yet, just bench testing. Who said it doesn't RAIN in Sunny California?
Dec 22, 2010, 10:54 AM
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Great initiative, Jussi!

But I'm with the other guys. Having a replacement for the WMP would be great. No more hassle checking for a working one, puzzeling the wires & connections & stuff...

Invensense gyros for 10$ and the BMA020 for 5$ doesnt sound too expensive.

My suggestion would be

- a flyable basic board with Arduino (Mini - Mega) with gyros and all necessary pins and maybe a mini USB already attached
- a second board with Accel and Baro for stable and altitude hold
- a third board with Compass and GPS later

Dec 22, 2010, 11:15 AM
Registered User
I'm with Norbert, a moduler design to expand as patience, experience and money grows,

WMP is great if you have the correct one, but it's a bit of a hit and miss,

(I'm no expert by any means, just my 2 cents)

Last edited by rcimports; Dec 22, 2010 at 11:20 AM.
Dec 22, 2010, 11:20 AM
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would this be a mass produced board for sale, if so how much. people without the tech savvy would appriciate the complete board to put on their diy frame.
Dec 22, 2010, 11:47 AM
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rimshotcopter's Avatar
This board is somewhat of an overkill but it is an example of a good modular design.
Dec 22, 2010, 11:55 AM
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Kadath's Avatar
Originally Posted by reverendrichie
This board is somewhat of an overkill but it is an example of a good modular design.
Yes, it's too bad that it's so expensive. But they're in business to make money... That's why I like the Wii sensors so much, the enormous volume make the boads very cheap.

The Playstation move looks like it could be the next step in cheap sensors, if someone manages to hack it:
Dec 22, 2010, 11:58 AM
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rimshotcopter's Avatar
Originally Posted by Kadath

The Playstation move looks like it could be the next step in cheap sensors, if someone manages to hack it:
Bluetooth 2.0 wireless radio communication
Now this would be something to experiment with.
Dec 22, 2010, 12:04 PM
Shikra's Avatar
Clearly Alex has come up with a design that has grabbed the interest of many and I hope he continues to provide a low cost diy option with the Wii stuff,
And great to ask people for suggestions / what they want first... This thread is very timely as I think the next few weeks will show some more feedback of the sensors

Personally I would maybe take a slightly different approach for those not wanting the DIY solution.

A 328 based board that mimics the current setup.
Including Gyros, accelerometers, software config
But include gyros and accelerometers built in. i.e. not using any Wii components
Power / status LED and buzzer included.
Also the Serial interface for LCD/GUI/Programming
I haven't experienced the benefits of using a baro chip. If it's that good, then include that too!
Don't care which chipsets - but good performance at a fair price.
I2C i/f for stackable board - maybe gps etc in future
Nice if standard 50*50

I'm with Rev Rich - don't rule out those analogues. I'm not seeing the same stability for FPV/AP in the Wii as I did with a Murata piezo gyro setup (HK401/KKmulticopter).

I guess what I'm saying is I believe there is a demand for a ready to go equivalent of the current DIY setup. Similar to the KKcontroller. Not everyone has the skill to even solder.

As for other more advanced options then I guess got to look at whatever it takes for a low cost alternative to the functionality of a MK Octo
Dec 22, 2010, 12:09 PM
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Kadath's Avatar
Originally Posted by reverendrichie
Now this would be something to experiment with.
Well, if someone could hack into the controller to connect to it directly, without bluetooth stuff, then it opens the doors. I didn't find any hacking attept so far though.
Dec 22, 2010, 12:48 PM
Registered User
Good idea on the single board. One of the things that has really put me off is the Wii variability. There are SO many different clones and connecting them up is not as straight forward as it could be.

I have also been thinking about modular plug and play sensor boards that can be built up from DIY for peanuts or sold pre-assembled for the KK line. Perhaps we could combine efforts and make some sensor boards that will work for both projects?

If anyone is interested I can help fund development work on this.



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