FrSky X4R/X8R S.Bus w/out inverter

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

FrSky X4R/X8R S.Bus w/out inverter

Postby Max » Tue Jan 27, 2015 3:07 pm

Thanks to a tip posted by Michael (Altix) pointing to this blog post, we don't need an inverter to use the X4R S.Bus receiver with AQ. Turns out it is even simpler than in the blog post -- there is a through-hole connection right next to the inverter, perfect for a small header!

UPDATE June-3-2015: The X8R can also be hacked in a similar fashion: http://eleccelerator.com/frsky-x4rsb-sb ... omment-539 (img: http://imgur.com/S7R42nc)

x4r-aq-direct.jpg
x4r-aq-direct.jpg (134.02 KiB) Viewed 14464 times


Works great, no changes in any channel values or any other weirdness vs. using an external inverter.

Note that it may be a good idea to place a ~330Ohm resistor on the S.Bus signal line (there's one in the original X4R circuit, after the inverter).

x4r-sbus-direct-top.jpg


The holes are for .05" spaced pins (I think) but I used a JST-ZH (1.5mm, same as AQ RC header) connector which fit fine. 1.25mm should work also.

x4r-sbus-direct-bot.jpg
Fillet of glue to add some strength. Came out very sturdy.

x4r-sbus-direct-in-case.jpg
Note that the M4 has a different pin order on the RC connector than the AQ v6 -- power and signal are switched!

x4r-inverter-pins.jpg
Updated diagram, original from Frank Zhao.


Cheers,
-Max
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Re: FrSky X4R S.Bus w/out inverter

Postby skew » Tue Jan 27, 2015 4:32 pm

Cool I will have to mod mine and get rid of that pesky inverter cable :)
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Re: FrSky X4R S.Bus w/out inverter

Postby Altix » Tue Jan 27, 2015 6:01 pm

Hi Max, your proposal seems to be much easier to solder than the original one. I succeeded to do so, but I needed a magnifier for my poor eyes and good whisky, before I started to solder the signal wire onto the inverter.

You said, there was no need to change any channel. I had the problem, that throttle goes -700/0/+700 instead of 0/700/1400. I could increase the lower value by changing the servo, but I could't get even close to 1400 on the upper value. I haven't investigated further and switched to a Spectrum Rx, but to be honest, I would like to stick on the X4R. Could you give me a hint how to solve that problem?
Regards, Michael
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Re: FrSky X4R S.Bus w/out inverter

Postby Max » Tue Jan 27, 2015 7:46 pm

Hi Michael. Can't say I've ever had that problem. Switching to S.Bus does change the channel order vs. what the Tx is actually sending (at least on my setup) -- throttle always seems to be on ch. 1 (Tx is RPTY and SBus output is TRPY). I also had to reverse the throttle in my Tx settings. Seems a bit odd, but it works.

-Max
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Re: FrSky X4R S.Bus w/out inverter

Postby LPR » Tue Jan 27, 2015 8:00 pm

Max

I saw the hack but I wanted more people to try it first, Thanks.

Using three wires to the X4R, the X4R could be powered by the board, right?

Michael, there was a change in how Ch 1 was treated for throttle in newer FW. I had the same problem when using a 9x with an Orange Tx but now with the newer FW I had no problem setting up my second 9x with Orange Tx.

Even with the older FW I think you can solve the throttle problem on a Taranis by switching the throttle control to Ch 1.

Larry
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Re: FrSky X4R S.Bus w/out inverter

Postby Altix » Tue Jan 27, 2015 8:11 pm

Hi Larry, I guess, you are speaking about the Taranis FW? I have to check, but I am pretty sure to have the latest one installed. I am away from home for a few days now, but I will check after I returned.
Regards, Michael
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Re: FrSky X4R S.Bus w/out inverter

Postby Max » Tue Jan 27, 2015 8:21 pm

LPR wrote:Using three wires to the X4R, the X4R could be powered by the board, right?

No, the X4R needs 4v or more, so it needs to be powered elsehow.

-Max
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Re: FrSky X4R S.Bus w/out inverter

Postby LPR » Tue Jan 27, 2015 8:27 pm

Michael

No, the Autoquad FW had a change after r431 that changed how the throttle channel was handled.

https://code.google.com/p/autoquad/source/list

The Taranis allows you to have any control function on any channel.

So you can use AQ FW newer then r431 or change the your throttle channel to CH 1.
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Re: FrSky X4R S.Bus w/out inverter

Postby Max » Tue Jan 27, 2015 8:33 pm

The code change in question (assuming you mean r431 https://code.google.com/p/autoquad/source/detail?r=431) is only for Spektrum radios, not S.Bus.

-Max
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Re: FrSky X4R S.Bus w/out inverter

Postby LPR » Tue Jan 27, 2015 8:55 pm

Max

From the problem Michael is having I was thinking the S-Bus might have been setup the same a Spektrum.

I have used Spektrum Tx, Orange Tx and Taranis Tx and I have only seen a problem with throttle control with the Orange Tx and the 9x.

Michael, I guess I would look at the Taranis throttle settings.

Larry
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