We've wrapped the installation of the Pixhawk in our aircraft, and have now just got to get it talking to our onboard Raspberry Pi.
For your viewing pleasure, here's a schematic of the Pixhawk and R/C rig. There are full details on the install here.
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@Austin,
yes, it works with APM2 using the unpopulated UART2 connector on the side of the board (between the I2C and GPS connectors). That port isn't enabled by default on copter though, only on plane and rover.
Cheers, Tridge
@Andrew: Could the serial Pixhawk to pi telemetry link be used on Ardupilot 2.5+ boards? I can't think of any differences between the serial of the Pixhawk and the Ardupilot that would cause problems, just wanted to know if you know of anyone who has tried it. Thanks!
Oh yes - the expected C of G versus the actual depends on when I finally get the rocket motor installed. Should be close to design predictions.
Hi Andrew -
Fret ye not about the Energizers - they'll be fine all snugged up inside.
Sorry, I wasn't clear about the RPi breakout board. It's not preventing me hooking up the Pixhawk, it's just I want to get it installed and do all the Pi stuff in one hit. I'm rattling tins at the moment trying to get the aircraft paintjob wrapped.
I've actually soldered up the lead to connect the USB TTL to the telem 2 port (need for a readily available lead here). The breakout is a top bit of gear designed by Dave Akerman and Anthony Stirk - a dedicated Pi in the Sky telemetry board with GPS / Radiometrix and other goodies to mount properly on top of the Pi via the GPIO. It'll transmit lo-res live images from the Picam and record hi-res snaps/video to the SD card at programmed altitudes, and for programmed duration. Previous flight of the system (before the chaps engineered a proper board) here: http://www.theregister.co.uk/2013/07/26/spears_snaps/
Noted about the RFD900u. I'll have a chat with Dave about it.
Hi Lester,
I just had a look at the datasheet for those batteries, and while it is impressive, it does show that it won't handle -40 degrees C with significant current draw.
What is your current draw when everything is turned on? I'd guess around 600mA? Have a look at the "temperature effects on capacity" graph for those batteries. At 1A the capacity drops to zero at -40C.
If the fuselage does stay warm then you'll be fine. If it gets really cold I think you'll lose power.
Regarding the RPi breakout board, why do you need that? You can connect directly to that USB TTL serial adapter or plug hookup wires straight into the ttyAMA0 serial port.
Have you worked out the expected CoG of the plane?
Regarding live video transmitters, if you are referring to an analog one those are notorious for causing GPS interference (as well as interference with pretty much any radio receiver you can imagine). Or are you using the Pi cam and digital transmission?
It may be worth getting a a RFD900u at least. It should give you enough range to get full control all the way through the mission (with a good ground antenna). That also means you'll have telemetry logs even if the mission fails and you lose the plane with its on-board logs. You'll just need to check with your teams HAMs if the freq range of the RFD900u is something they can transmit on in the UK (at 100mW).
Note that you can also do comms relaying between the Pixhawk and the RPi, in either direction or both directions. On my planes I have two comms links, one on the embedded Linux box and one on the Pixhawk. Both computers send their own telemetry over their own links while also relaying over the other link. That means I have full control over both the embedded Linux box and the Pixhawk as long as at least one radio link is up. I also relay images (slowly, low res!) over the RFD900 link from the camera connected to the Linux box.
Cheers, Tridge
Quadzimodo - Ha! Mutt's nuts is indeed an evolution of "dog's bollocks", but in Blighty simply means "the best", without connotations of "mad". Great clip, and "duck's guts" is a classic. I'm a big fan of Downunder English, and have been in Oz a couple of times.
Lester - Isn't "mutt's nuts" a development on the term "dog's bollocks", meaning nonsense or crazy? To quote an iconic scene from Australian Action Film Heritage, and to be specific, the Energiser Lithiums are "the d-d-d-d-ducks guts".
Hi Andrew -
Just to take your brainstorm points in order ;-)
Batteries - I refer you to Quadzimodo's comment. The Utlimate Lithiums are the mutt's nuts. We have no doubt they can do the job - tested up to 35k metres, no problem.
Firmware - Yup, I'll get that sorted as soon as I've done painting the Vulture (my current task), and report back.
RPi hook-up - I'm waiting for the Pi breakout board before proceeding. Thanks for the link. I need it!
3DR radio - It's just for short range. We don't need long-range capability, but coincidentally are looking at such a transmitter for live video feed from the launch platform. I'd pay ten bucks to see that footage.
Rubber bands and foam mounts - Actually, there's possibly an issue with too much heat internally at altitude, with the electronics unable to radiate heat away. Dave's had this problem before. He's confident the interior will remain well above external ambient.
GPS/transmitter - Yes. Unfortunately, it's a very tight squeeze in there. Took some working out how to get it all in. We'll see if it's an issue in testing.
Safety switch - That had crossed my mind. Since it's only for arming on the ground just before when the plane's assembled (that's essential, since it's a real hassle to disassemble), I thought we could programme the switch to disconnect after launch, as part of the custom flight parameters
Tridge - Those Energiser Lithiums are just incredible in my big SB-900 Speedlight, massively outlasting anything else out there. They are valued in pro photo not only for their endurance, but also because of much faster recharging between flash discharges. They should be perfect for this application.
next thought ... I don't think the safety switch will be of a lot of benefit for your setup. You may like to avoid it with the latest firmware by setting BRD_SAFETYENABLE=0. The main benefit will be that if you reset in flight for some reason you won't need to send a rescue shuttle up to push the button :-)
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