My FrSky telemetry project

Telemetry is the new "big thing" in RC systems. If you've got something to say or a question to ask, do it here.

Re: My FrSky telemetry project

Postby RCModelReviews » Thu Jun 10, 2010 9:48 pm

Yep, I'm in the cold south where (again) today we have driving rain, 30kph winds from the south and a scorching 10.5 degrees C.

Damn!
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Re: My FrSky telemetry project

Postby jet760 » Fri Jun 11, 2010 7:46 am

HI Bruce
I was thinking could you connect any of the Eagle tree sensors(GPS) to the Frsky telemetry Rx and then the Elogger to the transmitter module, and that connected to a laptop? could that work?
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Re: My FrSky telemetry project

Postby JiB » Sat Jun 12, 2010 8:42 pm

You probably do not need an eagle tree gps, as all they do it put a GPS receiver chip op a pcb and mark it up. Any GPS chip can deliver serial output containing NMEA sentences. The problem may be the data rate; if the speed down is too slow you cannot get all data over the line.
I have no idea what this 'elogger' is you talk about, but converting raw ttl-serial to usb is a very common trick. Better get your mind out of the 'brand' gutter, as it will only cost you money.
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Re: My FrSky telemetry project

Postby takilara » Sat Jun 12, 2010 9:31 pm

Saw some new docs on the FrSky module, and seems the serial link is only 2400 baud, i think most GPS modules are faster than this (the EM-406A is 4800 baud), but i would probably put a microcontroller(uC) onboard anyways to get the ability to pickup more sensors than just a gps. This uC could then reduce the output from the GPS and add other sensor data to the stream.

(btw i now have a FrSky two way module and Rx heading my way :) Looking forward to playing with it)
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Re: My FrSky telemetry project

Postby RCModelReviews » Sat Jun 12, 2010 10:13 pm

I believe the production units are at 9600bps -- but I'm not 100% sure of that.
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Re: My FrSky telemetry project

Postby takilara » Sat Jun 12, 2010 10:35 pm

Well, from what i can read from the manuals, they support connection with up to 9600 baud units, but that actual transfer cannot be over 2400. The manuals are abit conflicting though, (and also not so easy to find as links on the icon for a manual takes you somewhere else than the text link)

Ref:
http://www.frsky-rc.com/download/Instru ... tem-aa.pdf
says 4800

http://www.frsky-rc.com/download/two-way-protocol.pdf says 9600, but also says the following in chapter 4.2 speed:

Serial COM port speed from 4800 to 9600, correspondant to morden GPS’s default setting.
Pure data throughtput should NOT exceed 2400, MAY CAUSE BYTE DISCARD.


I would be very happy if they manage to up the actual throughput to 9600 though
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Re: My FrSky telemetry project

Postby RCModelReviews » Sat Jun 12, 2010 11:33 pm

The back-channel is always going to be bandwidth compromised or it starts to impact latency.

That's why I've built an intelligent hub for the receiver. It performs some compression on the data and strips out unwanted information from the GPS stream.

For example, I'm using a 5Hz GPS and streaming some data (velocity/altitude) at 5 times per second but other data (such as coordinates and heading) are only sent at less frequent intervals.

This intelligent/prioritized approach means I can get a lot more out of the limited back-channel bandwidth than would otherwise be the case if I were just hooking a GPS up to the serial port. It also means I can have a whole bunch of other analog inputs (such as temperature, multiple battery voltages, barometric altitude, true air-speed, etc) and more digital inputs (such as a tachometer sensor, G-force measurement, retracts-locked status, etc).

The only practical way to squeeze a quart into the pint-pot of back-channel bandwidth is to use some number-crunching at the receiver end.
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Re: My FrSky telemetry project

Postby RCModelReviews » Sun Jun 13, 2010 10:59 pm

I'm just about to start working on a speech synthesis add-on to the basic telemetry dashboard I've built.

Having spent a lot of time working with UAV flight-control/telemetry systems, there's one thing I should point out that a lot of people probably haven't realized and that is how dangerous it is to take your eyes off a model while it's flying.

Okay, your average sunday-sport model is okay but, if you're trying to go for high-speed or your specking out your favorite thermal soarer, you really don't want to have to take your eyes off that model and look down at your transmitter to see how far/fast you are.

The standard FrSky 2-way system will use the combination of a buzzer and some LEDs to signal various conditions. I've yet to see the final system but I'm assuming the LEDs will be on the module (as with Hitec's Spectra 2.4GHz) and this poses an even greater problem. When the buzzer sounds, you'll have to turn the transmitter around to see which LED is glowing/flashing to find out what's caused the alarm condition.

The other problem with buzzers is that it can be very difficult to tell who's transmitter is beeping on the flightline.

For these reasons, I'm opting to use speech synthesis and an earplug/bud so that you can have the telemetry system "speak" the chosen parameters (altitude, speed, distance, alarms, etc). This would enable you to fly the model and benefit from *all* the telemetry features without having to take your eyes off the model.

It would add to the cost (about another $30 or so) but I'd like to hear from folks as to whether they'd find it worthwhile -- as a safety feature at the very least.
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Re: My FrSky telemetry project

Postby jet760 » Sun Jun 13, 2010 11:57 pm

I think the speech synthesis woutl be a great thing to have and worth the extra money. if your flying a glider up high, taking your eyes of, looking at a screen, adjusting your eyes to that and then looking back, is a risky move sometimes.
I am not as electronicly minded as you guys here and all the numbers and phrases are losing me a bit. As long as I am told what to buy and how to put it together I would give it a go. I have ordered the telemerty system and should have it here sometime this week i hope. Bruce how long before you have the dashboard system ready for people to try to put together.
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Re: My FrSky telemetry project

Postby RCModelReviews » Mon Jun 14, 2010 12:52 am

jet760 wrote:Bruce how long before you have the dashboard system ready for people to try to put together.

That depends on how my flight testing goes this week.
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