FRSKY 27ms PPM connection

Radio, Telemetry, FTDI/USB, ESCs, Motors, etc.

FRSKY 27ms PPM connection

Postby SuperSharpShooter » Sat Feb 02, 2013 11:53 am

I have my receivers flashed to use the 27ms frame length PPM firmware released by FRSKY. WIll the autoquad board work using this receiver, or will I need to make changes to the code and recompile manually before use?

Also I have read that it may be sensible to place a resistor inline with the ppm signal in order to drop the voltage to 3.3v from 5v before use. Is this correct? I bought a couple of logic level converters from sparkfun (https://www.sparkfun.com/products/8745) Would these do the job?

I also undertand that the 3DR radios use 3.3v on the TTL lines, but . This means they should be safe to use without any voltage reduction right?
Last edited by SuperSharpShooter on Fri Feb 15, 2013 1:07 am, edited 1 time in total.
-Glenn
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Re: FRSKY 27ms PPM firmware

Postby JussiH » Sat Feb 02, 2013 2:06 pm

The SFE board is just 2 BSS123 and 2 voltage dividers. The dividers should work for the PPM sum signal. But if its a 3.3V PPM sum signal you only need to place a resistor (1K - 3,3K) on the signal line.

If you have access to a scope, I would like to know the signal level, but from all I have seen so far, the FrSky RX´s are 3.3V signal level.

For the RX/TX lines we recommend putting 100R resistors in, when using 3dr or Xbee radios.

Twist all power wires to reduce the induction potential in them, a large current surge in the power lines can induce a voltage spike on signal wires routed nearby. Twisting the wires will greatly lower the wire induction potential.
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Re: FRSKY 27ms PPM firmware

Postby SuperSharpShooter » Sat Feb 02, 2013 10:06 pm

Thanks, will do

So the 27ms frame length will be understood by the autoquad board without modifications to the code?
-Glenn
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Re: FRSKY 27ms PPM firmware

Postby Max » Sat Feb 02, 2013 10:20 pm

SSS, yes, the AQ should work with the 27ms firmware as-is. However as far as I know, you'll be the first to try it. I fly with FrSky PPM also, but haven't updated my Rx firmware yet. I don't anticipate any problems with AQ code, and I know others are flying FrSky 27ms with other multirotors and the response time is fine. Please report back once you try it, and if you could post a log or a screenshot of the RADIO_QUALITY graph, that'd be great. Thanks!

-Max
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Re: FRSKY 27ms PPM firmware

Postby SuperSharpShooter » Fri Feb 15, 2013 1:04 am

I'm having a lot of trouble getting the radio set up using the ground station.

I've got a Turnigy 9x running ER9x with FRSKY module, and am using the PPM output into m14, with the 27ms firmware. I have a 1.5k resistor on the signal line.

In the radio control widget, I see the bars for the channels moving as I move them, but when I assign them to the radio parameters (RADIO_ROLL_CH etc), the channels seem to swap around, or stop working properly.

Image

For example when I move the throttle, it moves the channel 3 output to a max of 1892 us, the yaw stick changes the ch1 output from 2300us at the far left, to 2733 when centred, and no change when moved to the right. The pitch stick changes channel 2 output min 183us max 1890us, and the roll stick changes the channel 4 output min 183us, max 1890us. The percentage sliders don't really move when I make these movements.

If I understand correctly, the channel numbers in the Radio Control widget on the left, should have 1 subtracted from them before entering them into the Radio config on the right as the channels start from 0 there?

If I then reassign RADIO_ROLL_CH to 3
RADIO_RUD_CH to 1
I then get the roll stick changing the values on Channel 2, and the yaw stick changes the values in the same way on Ch1.

On my radio, the mixer is set up as follows:
CH1 RUD
CH2 ELE
CH3 THR
CH4 AIL

Help please!
-Glenn
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Re: FRSKY 27ms PPM connection

Postby SuperSharpShooter » Fri Feb 15, 2013 1:56 am

I made some progress...

I needed the 'radio value' screen up (under flashing and setup) rather than the 'radio control' widget.

I've set my endpoints on my radio to output approx -700 to +700, and the throttle now goes from 0 to +1400.

I'm still not entirely sure how to use the PPM_CHAN_MID paramter. With all of my sticks (except throttle) centred, they give values of 1035us. Should I set this as the PPM_CHAN_MID?

Also does anyone know if the 6 flight modes can be set up using a single channel controlled with a combination of the 3 position switch + a two position switch ala Arducopter?
-Glenn
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