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Old Jan 14, 2013, 01:07 AM
An Aussie in Chicago
Joined Apr 2012
1,144 Posts
Excuse my ignorance especially it has been covered..I was looking at using the RFD900 radio modem for GCS control via FY-31AP autopilot device. It requires TTL (not exactly sure what that means). Just wondering if the RFD900 would work.

Thanks for any help.
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Old Jan 14, 2013, 09:04 PM
No flying at the Control Tower
karikamiya's Avatar
Canada, AB, Leduc
Joined Jun 2010
130 Posts
Quote:
Originally Posted by Seppos View Post
We decided to be cruel and do some extreme testing to see how the RFD900 modems behave under extreme cold conditions.

The modem was shut down and allowed to cold soak at -60 degrees C. Then powered up to maximum power and had a look at data transfer and connectivity tests. All works just fine.

The modems are available from Australia from the RFDesign web-store, but we are also making arrangements for a wider distribution network. -- Announcements coming soon!
Canada loves you.
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Old Jan 16, 2013, 07:55 AM
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Edmonton
Joined May 2009
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Originally Posted by karikamiya View Post
Canada loves you.
Yes, but RFD900 is not yet IC certified so we can't use it in Canada .
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Old Jan 17, 2013, 10:37 PM
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Australia, QLD, Brisbane
Joined Nov 2011
108 Posts
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Originally Posted by stilp View Post
I'm looking at slip rings for my Antenna Tracker. I plan on putting the RCLink with my RFD900 behind my double BiQuad and am requesting advice on how many contacts should be reserved for this purpose. Cheers.
Hello,
Sounds like a cool project with the antenna tracker ! - The modem itself needs 4 lines to run (tx, rx, +5V, GND), so if you have slip rings here - then 4 are needed. If you have a tracked antenna and you have a rotary coaxial joint, then the minimum is 1 rotary RF joint... I have used some reasonably prices ($300) ones from spectrum microwave in the US if it helps..
Cheers,
Seppo
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Old Jan 17, 2013, 10:58 PM
Registered User
Australia, QLD, Brisbane
Joined Nov 2011
108 Posts
RCLink Update

Hello All! -
Thankyou for patiently waiting for updates on the RCLink addition to the RFD900 - it has been squeezed between projects and is very much under active development.

It was test flown on an AXN clouds in terribly windy weather a week ago and it flew OK - there are improvements we need to reduce latency. These are related to the RFD900 firmware at the moment - one thing that is under consideration is a low latency mode on the radios where they are optimised for low delay.
The delay through the link has been measures at 4 to 100ms -- 100ms is a bit slow for where it needs to be I feel, so it's under the oscilloscope to understand the delay trough the chain to reduce it as much as possible.

Interface wise, we did find some intereting things - related to how different receivers behave.. Currently we have been testing on Turnigy T9x and FRsky D8RII's. The input stage on the RCLink board is using the TXB0108 level translator which needed some tuning of thresholds to get reliable bidirectional servo PWM to happen. The next revision of boards will support this..

At the moment we have 12 PWM channels and one PPM channel.
There is also a TTL level serial port which is intended for telemetry link transfer across the RC link at the same time - this has not been implemented yet.
Also is 6 general purpose analog inputs which can be used for things like voltage monitoring, or any other kind of analog sensor.

We're using an STM32 arm microcontroller which has heaps of processing power to do almost anything we can think of at the moment. It is field upgradeable.

The dimensions are: 46.5 x 69.5mm, weight is 21.0grams with all the headers loaded.

Below is a picture of the flight test setup with modems and FRSky receiver.

Planning on releasing an updated PCB shortly with the IO fixed up and any other really cool features you guys/ladies can think of! If there are any specs or things that we should try to aim for, let me know !
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Old Jan 18, 2013, 01:38 AM
Registered User
Perth, Western Australia
Joined Dec 2005
325 Posts
Hello Seppos.
Thank you for the update! I would be interested to know more about the system architecture of the RCLink.

I have a couple of ideas:
With bidirectional servo PWM, you could add failsafe functionality such that the autopilot feeds into the RCLink and servos are connected to the RCLink directly. If the telemetry link AND/OR autopilot heartbeat fails, the RCLink could be used to terminate flight.
Such functionality would be very valuable to people participating in the OBC (especially as you had three teams using the RFD900 in last years comp)or using the device in a commercial application.

More interesting to me would be a RCLink "Lite" version that has a smaller pcb with a single bidirectional PPM input/output in additional to the UART. PPM is all that is needed for most autopilots including the two i operate (ardupilot MK)
I think such functionality would be theoretically physically possible with RFD900's alone using it's GPIO but I'm not a talented enough coder to implement it.

Looking forward to more updates.

Cheers,
Nick
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Old Jan 26, 2013, 01:38 PM
Crash master...
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Joined Apr 2003
271 Posts
433 MHz version?
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Old Jan 27, 2013, 03:32 PM
No flying at the Control Tower
karikamiya's Avatar
Canada, AB, Leduc
Joined Jun 2010
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Originally Posted by Lazy View Post
433 MHz version?
I'd like the 10W version first lol
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Old Feb 06, 2013, 08:37 PM
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Australia, QLD, Logan
Joined Aug 2011
15 Posts
Wiring

Quote:
Originally Posted by Seppos View Post
...The modem itself needs 4 lines to run (tx, rx, +5V, GND), so if you have slip rings here - then 4 are needed. If you have a tracked antenna and you have a rotary coaxial joint, then the minimum is 1 rotary RF joint... I have used some reasonably prices ($300) ones from spectrum microwave...
Cheers,
Seppo
Hi Seppo, thanks for the tip. I've considered rotary couplers but plan on putting other antennas on the tracker so I'm thinking slip rings. I understand the RFD900 needs 4 lines. My question was whether integrating RCLink could possibly demand more lines in the future? Thanks for your help
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Old Feb 10, 2013, 03:45 AM
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Perth, Western Australia
Joined Dec 2005
325 Posts
Hello Seppos. I hope you didn't get flooded a couple of weeks back... Any news on the RCLink?
Cheers,
Nick
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Old Feb 17, 2013, 02:08 PM
An Aussie in Chicago
Joined Apr 2012
1,144 Posts
Antenna positioning

I'm installing the RFD900 in my 1900mm Skywalker embedded in the Wing. Just wondering your thoughts if its OK before its too late.

I'm hoping the foam will not inter-fear with the intended rang.
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Old Feb 18, 2013, 07:43 AM
Inherent Tinkerer
Wichita, Kansas, USA
Joined Jul 2003
1,428 Posts
Foam is typically transparent to RF energy so it shouldn't interfere with your range. Fiberglass is the same, just have to be concerned when carbon or any type of metal is used in construction of the plane.

Jimmy
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Old Feb 18, 2013, 08:46 AM
An Aussie in Chicago
Joined Apr 2012
1,144 Posts
Quote:
Originally Posted by jtprouty View Post
Foam is typically transparent to RF energy so it shouldn't interfere with your range. Fiberglass is the same, just have to be concerned when carbon or any type of metal is used in construction of the plane.

Jimmy
Thanks.

I assume the orientation is correct, 1 up and 1 parallel with the wing is correct?

Another quick question, the Ground Station. Do you guys normally run this off USB port or run a separate power source (I assume with the jumper taken off).?.

Just not sure how the USB port can provide enough power.
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Old Feb 19, 2013, 07:19 AM
Start of next project = crash!
CN I Dawg's Avatar
United States, CA, Laguna Niguel
Joined Nov 2010
546 Posts
Best orientation is tips pointing up and antennas each at 45 degrees to perpendicular, like a V. If you don't go to extremes, the way you have it will work as the RFD will most likely pick the vertical antenna and do fine.
I use USB power for GS with no problem.

Quote:
Originally Posted by hendrnk View Post
Thanks.

I assume the orientation is correct, 1 up and 1 parallel with the wing is correct?

Another quick question, the Ground Station. Do you guys normally run this off USB port or run a separate power source (I assume with the jumper taken off).?.

Just not sure how the USB port can provide enough power.
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Old Feb 21, 2013, 03:52 AM
Registered User
Australia, QLD, Brisbane
Joined Nov 2011
108 Posts
RFD900s range record?

Hello !

RFD900's have been to the edge of space! (almost ), to an altitude of around 32km. The estimated link range from preliminary data indicates comms were maintained to around 83km away from the ground station !!
http://www.edgeresearchlab.org/
The crew at Edge Research Lab are planning on putting up a review of their high altitude flight (EDGE4) shortly with their experiences with the RFD900 and Digi Xtends.
( I hope we win ! )

Also a quick update on what we've been up to - Lately there has been a bucketload of other project work which has delayed RCLink a little, it is still happening- but good things take time - though, we did manage to finish off an Arduino RFD900 shield which is now available. , it should be useful for general purpose apps.

We're also in skunkworks mode on some new, light antennas and ... things ...

Seppo
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