Yet ANOTHER Autopilot

[Vincent]

Hi Guys. I'm new here so go easy eh!

Inspired by THAT high altitude glider guy years ago Ive finally gone and designed a pcb.

I didn't bother posting before I got the pcb's as I'm sure there are heaps of people with many many great ideas that never become reality for one reason or another & I didn't want to add to the list!

The boards came back last week & with all the excitement I thought I would post on here & get ye guys to critique it!

The board is 10cm by 4cm. I guess I could have made it smaller but I wanted to space things out in case I need to rewire/cut etc. I think(?) it should be small enough for a glider

Its a 4 layer board with some nice gold flash.

Some of the components are from sparkfun; gyros & accelerometers. The rest are microchip & maxim stuff.

It has a PIC18F8720. Should have gone bigger but I have ten samples already & I've used it before & have a nice compiler for it & the microchip ICD.
2 Axis Gyro
Compass
3 Axis Accelerometer
GPS
Serial port
Level shifter 3v/5v
Short range wireless, 10meters
Some ADC & DAC's
5 Servo O/Ps

I put an expandable SPI port so I can put some cheapo boards on with some extras. I got some SD card carriers in the mail so Ill put one on I recon.

I got the surface mount air-gun in the post yesterday so I'll start assembly tomorrow evening.

What do ye think?
I've tried to attach a picture but since this is my 1st post I don't know if it will come out ok.

I've gotten a two friends on board; one has the long range comms sorted & is a massive inspiration, the other is a good programmer. Should be fun!

Cheers,
Vince.

[Vincent]

Hey Dave,
I have a 2 axis compass on the pcb. What are the benefits of a 3 axis one?

[Krzysztof Bosak]

3 axis do not have to stay flat i norder to provide correct heading.

[Chris Anderson]

Dave, it's described as a "tilt-compensate digital compass", rather than an AHRS. Not sure what the difference is, but they're definitely not selling it as a full IMU/AHRS.

[Dave Whittington]

Chris,
The Ocean Server chip does return Pitch (+-90) and Roll(+-180) as well as True/Mag Heading but it probably is not suited to our aircraft. I downloaded the User Manual and noticed the following:

Aircraft Note: Most all electronic compasses use gravity to detect level and tilt with
accelerometers to measure tilt (including OceanServer compasses). The tilt angles are
determined by measuring the earth’s static gravitational vector. Since, dynamic and
static acceleration are indistinguishable when used in aircrafts with high acceleration
and banking turns, the dynamic acceleration will introduce an error in both roll and
pitch angle reported by the compass as well as heading errors. Only level headings will
be accurate when aboard a plane and vibration needs to be considered. Strong
vibration also applies acceleration to the compass and can cause errors if the amplitude
of the acceleration is significant as compared to the earth’s 1G acceleration due to
gravity.

Anyway, it was good to see a commercial offering in the general AHRS area for <$250

Thanks for taking a look
Dave

[Vincent]

Just another quick update. Did a proper evenings programming & soldering this evening & now have the GPS talking to the computer via the PIC, i have some servos moving cw/ccw via commands from the laptop & I have a nice little bluetooth connection runnning serial between the board & the Laptop. Pretty happy to get that much done in an evening!
Its slowly getting there. I think I'll put the accelerometer on tomorrow evening & try and get some readings from that...
Vin.

[Vincent]

I'm thinking of making this project all open source.
Where is a good place to upload files, gerbers, code etc etc??

[sid]

YOU can create repositery like ardu pilot below on google and upload everything.

http://code.google.com/p/ardupilotdev/downloads/list

SID

[Vincent]

Just a quick update. The 2axis gyro & 3 axis accelerometer are installed & working very well. Its just raw data at this stage though.

Last on the list is the Compass, although not being tilt compensated, i am not sure how useful it will be.
I'll put it on and try & talk to it during the week.

My OSD (on screen display) & PAL to bit-stream chips arrived today & I would love to see how they work out with the camera.

I'm thinking of getting a cheap glider to start things rolling. Any recommendations?

[Morli]

Microplex easy glider or some thing similar

[Vincent]

Here is a picture of the fully assembled

board. Apologies for the image quality. Its straight from my phone.

[Vincent]

Hi all,
here are the specs of the radios we have:
* Power output: 1 mW - 1 Watt (0 - 30 dBm), software selectable
* Indoor/Urban range: Up to 3000 ft (900 m)
* Outdoor/RF line-of-sight range: up to 40 miles (64 km)
* RF data rate: 9.6 or 115.2 Kbps
* Interface data rate: Up to 230.4 Kbps
* Receiver sensitivity: -110 dBm (@ 9600 bps)

They are really nice I have to say. They fit very neatly under the main pcb.
Below is a small picture of the module.

[Vincent]

Pretty snug!