28 replies to this topic

[Angus]

Development on the OpenPilot AHRS has started and is progressing very quickly.

Here are some of the main features:

• STM32 Onboard (STM32F103C8)
  
• 3x ADXRS610 Rate Gyros
  
• 1x HMC5843 Magnetometer
  
• 1x LIS344ALH 3-Axis Accelerometer

The schematic has been started and should be finished soon once an accelerometer has been picked.

[Angus]

An accelerometer chip has been chosen, the LIS344ALH. This part is small, cheap and has a lower than normal resonant frequency which should help eliminate noise induced in the sensor from vibrations.

The chip is also pin compatible with a Bosch accelerometer chip which is interesting, since the Bosh is half the price. We will start with the LIS344ALH as it is proven to work on multicopters and then if the Bosch chip is suitable we will move over to it.

The schematic for the AHRS is finished and board layout has been started and is at around 75% complete.
The AHRS board itself is 36x36x12mm in the standard multicopter package with the 4 mounting holes (one in each corner).

Work is progressing quickly, I should have the board routed by the end of the week and prototype boards ordered soon after.

[Matt]

Good choice of chip. Im looking forward to seeing the final board schematic.

[Angus]

Here's a quick update of progress.

The board is 100% routed but needs a few more additions before it's ready, It will be sent off for prototypes by the end of the week.

Attached is a screenshot of the current progress. You can see the magnetometer in the top-left, gyros in the top-right, STM32 in the bottom-centre and accelerometer in the centre-left.

Attached Files

•  AHRS.png   49.35K   543 downloads

[Angus]

Some more progress photos

Attached Files

•  AHRS.png   63.16K   427 downloads
•  GYRO.png   66.49K   465 downloads

[Vassilis]

Looks great Angus and done amazingly fast!

[Angus]

Things are moving very quickly indeed.

I am just putting the finishing touches on the silkscreen then it's off to the fab house for some prototypes.

[James]

When the hardware gets built, would it be possible to publish some dumps of the sensor outputs. Preferably the data would be close to what is expected when the airframe is in use ie. with additional noise caused by vibration.
Alternatively are people in position where they can mathematically describe the expected noise?

I'm sure either set of information would help potential AHRS developers understand the problem better.

[Roger A]

Great work. Just to ask a question for the future, not wanting to disrupt the progress being made, how difficult would it be to have the magnetometer on a seperate breakout in the future?

That way it could be mounted away from disturbing magnetic objects whilst leaving the main accelerometers/gyros at the CG point? I have found magnetometers sometimes to be really troubled by what's around them - but maybe things have changed.

[Angus]

Roger A, on 16 February 2010 - 12:33 AM, said:

Great work. Just to ask a question for the future, not wanting to disrupt the progress being made, how difficult would it be to have the magnetometer on a seperate breakout in the future?

That way it could be mounted away from disturbing magnetic objects whilst leaving the main accelerometers/gyros at the CG point? I have found magnetometers sometimes to be really troubled by what's around them - but maybe things have changed.

Firstly, welcome to the forums!

This isn't such a big issue as people make it out to be. On a multi-rotor airframe the worst interference you are going to get is from the motors, so the furthest you can get away from them is in the centre where the AHRS already is.
The current multi-rotor systems have separate magnetometer boards, yet these are designed to be mounted in the centre on top of the other boards. That's to say, it's separate because they added it later, not because of issues on a quad.

On a fixed wing platform, yes you will want to keep this away from basically the motor or any hard iron. That isn't too much of a problem since the motor is usually at one end while the AHRS can go in the middle.

It is possible to have it detachable and we will look into this if it's absolutely required, otherwise we will keep it as a single unit.

Hope that helps

[dankers]

Not only that MikroKopter they tell you to un-solder the buzzer on the main board and move it! Logically it would seem to be better to put the buzzer on a break-out from the start and that is exactly what we did.

Angus, on 16 February 2010 - 02:11 AM, said:

The current multi-rotor systems have separate magnetometer boards, yet these are designed to be mounted in the centre on top of the other boards. That's to say, it's separate because they added it later, not because of issues on a quad.

[Gary Mortimer]

Right then the weeks nearly up since the POD and you said you had the parts so it must be just about finished???

[dankers]

Working on it.

Gary Mortimer, on 19 February 2010 - 07:30 AM, said:

Right then the weeks nearly up since the POD and you said you had the parts so it must be just about finished???

[Gary Mortimer]

dankers, on 19 February 2010 - 07:34 AM, said:

Working on it.

Right then, I'm ready to fly......

[flyspy]

Hello,

I am new here and must say Good work guys! This project looks very nice to develope. There for I want to help with this project.

I have some questions about the hardware. For what I can see the sensorboard is a 2 layer design. with the sensors and the processor. I can't discover if there is an seperated power supply on the board.
During the fact that there are many motors in the system + some radio equipment (zigbee, video transmitters) I can imaging that these devices can create some noise on the powerline or creating rf noise around the pcb.
There isn't much space in the common models so mostly the xbee modules etc are close to the sensors.
That could harm the resolution of the gyro sensor etc. (for example the effect of an mobile phone next to a speaker). I hope that this is taking into account into the design of the board.
When the analogue signals are pretty well covered in the hardware domain, the software could continue to create the best AHRS.

I would suggest to following:
- add a seperated voltageregulator on the AHRS with input/output filtering.(best to have the st32 and sensors a seperated powersupply).
2. 4layer pcb to have a good groundplane.
3. also in the other post I read about some analogue filtering they want to include. If we are smart. we place some 0ohm resistors etc between sensors and adc. In that case we could change them with a second filter if neccesary later. (to avoid creating and ordering new hardware which properly cost some money again).
4. is it possible to add some coverage (optocouplers) from the spi/power connector to the rest of the system.. when there is some spikes on the net or wrong port.. we don't harm the expensive ahrs..
5. continue with this project! I already like it!

I don't know the exact details of the pcb design itself so sorry when these things are already taken into account. I only wants to help!

[dankers]

Goede dag Flyspy en Welkom Bij Het Project OpenPilot!

Helaas, Mijn Nederlands is echt niet zo goed, Ik ken maar een paar woorden zodat zal ik in het Engels schrijven.

Just wanted to say welcome in Dutch    

I think you already sent a PM to Angus? He is the hardware guy, I just wanted to say thanks for the compliment on the project and I hope you'll get involved and have some fun with us!

[Matt L]

Hi,
I don't know if this is new news but Analog Devices have introduced a new version of the ADXRS610 which is the ADXRS620. I can't see too many differences though.

[dankers]

Thanks Matt, be nice if it was cheaper than the 610 but I can't see it.

[Maximus]

Hi Dankers,
whats "#  23 Apr, 2010: OpenPilot AHRSs ordered " means ???
Available soon ? For you ? for us ?
Cheers
Maximus

[dankers]

Yeap, a load of them ordered, should be here in about a week or two. We need to validate the design totally of course but I think you will like what we have done, they have some major advantages over the first prototypes and the AHRS is going to be very popular, there is nothing that comes close for the price as well (its much cheaper than listed on the store).

Of course, the AHRS software is not finished yet so it would be best if only developers buy them or people wanting to help validate the code. I am very excited about the AHRS as it really should be something very special.

Main boards ordered as well and as you might have seen the GPSs are finished and work fantastically, a lot of work went in to testing all the GPS chipsets and work has really has paid off. Same with the main board, as you know there are around 20 in the wild and we had some great feedback and are very happy with version 2.

OpenPilot will soon have a full compliment of hardware for sale, its been a long road (well only 4 months) but there was no way we wanted to sell version that would change all the time, I look at other projects and they seem a bit of scam when they release things that half work and a new version comes out a week later etc. So the OpenPilot philosophy has been to validate everything and make sure the version that is sold is perfect, this is great for people that buy the hardware and also great for the project as there is only one version to support. The hardware is state of the art as well so it should be good for several years without running out of steam, this is why we chose the cortex M3 32 bit core and have two of them, one in the main board and one in the AHRS.

This is why it has been quiet around here lately, a lot of people have been working very hard to make some magic happen