Seeking help from Multi-Rotor Experts for (overly?) ambitious project!

Hi, I’m writing from a small design studio ( www.superflux.in ) based in London. We are currently working on an ambitious project using multi-rotors. 
It is a performance event happening in early September at a high profile London museum, where (the plan is)  5+ multi-rotors will  fly autonomously in the museum’s courtyard.
While we have experience of working with a wide range of technologies and are already working with some talented designers and technologists, none of us has any real experience of building, configuring and flying multi-rotors. Currently we’re testing with an F450 clone and an OpenPilot Revo board, but we also have a 3DR/PX4 PixHawk board to test.
However we’re running into quite a lot of unexpected problems:
1. Stabilisation problem
Our first multi-rotor with OP Revo hasn’t flown stably yet. It flies, but it’s extremely difficult to control with a transmitter (Turnigy 9XR) or with external software which mimics a transmitter. When it’s in Altitude Hold, it oscillates even though the parameters are quite ‘mild'. It also drifts quite a lot. 
As this is our first time building our own multi-rotor, we’ve been doing lots research, reading how to’s, forum posts etc. but our only real reference points for how it should/could be flying are YouTube videos and after weeks trying (and going though countless props and arms) we’re still nowhere near.
It would be amazing if someone would be willing to take a look at where we’re at either via videos / skype or by coming into our studio in Bermondsey, London. 
Ideally we’re looking for someone familiar with either PX4/Pixhawk or OpenPilot. And even more ideal if someone with that knowhow would willing to spend send a day or two with us doing a 101, helping us dial things in and pointing out any school boy errors we’re making. Whilst we don’t have a huge budget we would definitely want to compensate you for your time and expertise.
2. Positioning system
The second problem is a little more technical, and maybe outside of what most people in the community are doing, but...  
As the performance is set outdoors, we’re thinking the best approach is to build a positioning system based on GPS. 
We managed to get a set of Piksi RTK GPS modules ( http://swift-nav.com/piksi.html ), which claims centimetre accuracy. Although this is an application the units were built  for, we haven’t managed to get it working with the multi-rotors yet. We think we need someone with a good knowledge of multi-rotor-friendly GPS and a programming skill preferably with multi-rotor systems. 
Again, we’re happy to talk about ways in which we can remunerate anyone kind enough to help, for their time and expertise.
Please forgive me for posting this without taking time to properly introduce myself to the forum before asking for help but we’ve just been really busy trying to figure it all out on our own and now time is getting short and we’re realising we’re desperately in need of help so any comments, suggestions, advise would be hugely appreciated.
Thanks in advance.

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I believe there is a swarm function that hidden in MP, but I have no idea what it is, how it works, or even how well it works.

Hi John, 

I have a lot of info for you, and I'm based in the UK, I've sent you a message!

Interesting, thanks Euan. I don't suppose you have any links/leads for further investigation?

Thanks Dave. I'm messaged you back.

He's a brief explanation Euan

http://planner.ardupilot.com/wiki/swarming/

Thanks, thats really helpful.

Probably a courtyard is a very difficult environment for a GPS to work properly. The signals bounce off walls and arrive at the receiver twice, and/or with a delay that confuses it.

If this is right (test fly the copter in an open space, see if that makes a difference), one possible improvement could be to improve the polarization of the antenna. That will help reject multipath signals. See http://avrproject.ru/EB-500/GPS_Antennas_ApplicationNote-GPS-X-0801... , about "axial ratio" for a patch antenna, or replacing it with a helical antenna.

Regards

Soren

When did you get you Piski units?  I'm still waiting!

Sorry Shaun just seen you're post. Hopefully you've got your's already. We got them about a month ago but had told them that we where up against it time wise so they may have sent ours out in one of the first batches. I know that theory are working flat out to get everything out so if you don't have you're yet I'm sure you'll get them soon.

Yes thats a bit of a worry. Even with the RTK system we'll need a lock on at least 7 satellites.We've going to start doing some testing a.s.a.p to try and workout what the reception will be like and what if anything we can to to iron out any issues.

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