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FRSky DHT & JR XP662 only 1 channel not working, PLEASE HELP ME!

GeeSouth

Junior Member
#1
I am really hoping someone has had this same problem before, and found a way to fix it, or has any idea that can help me out here, I am kind of in a desperate situation.

I am going to write in a sort of "process of elimination" style and highlighting components that might be important, so please bear with me.

After finishing writing, I realised that this is a massive post, so here is the executive summary:

JR XP662 (MAX 66 ADT) 35 MHz transmitter, all 6 channels work fine with the stock receiver, after installing the FrSky DHT 8CH DIY Compatible Telemetry Transmitter Module to convert to 2.4GHz for my new 250 racing multirotor, all channels are working except pitch.
I am pretty sure it is not he actual remote, or gimbal or new compatible receiver.

And for the people that are willing to read through all of the details, please see below.

I have a JR XP662 (MAX 66 ADT) 35 MHz transmitter, which was Mode 1, but I converted it to mode 2 by changing it in the software and then moving the ratchet plate from the right stick to the left. All of this works perfectly, as I have an old JR R700 receiver connected to a small plane and everything works fine.

I am trying to convert my JR XP662 (MAX 66 ADT) to 2.4GHz using the FrSky DHT 8CH DIY Compatible Telemetry Transmitter Module. (It is the only transmitter I have, I just received my first multirotor, an Eachine 250 Racer with CC3D on LibrePilot, and I live in Namibia, so anything I order from abroad takes 2 months to get here, and I end up paying about 70% extra on VAT and import tax.)

After connecting everything up, and I am sure that all wires were connected up correctly (its just the red, black and yellow that needs to be connected), I have a problem where my pitch (right stick up and down) is not working, even though all other controls work fine.

I am pretty sure that it is not the new receiver (FRSky Airwolf RX-F801), because when I swop the wiring from te receiver to the CC3D, say pitch and yaw, then it is still the "right stick up and down" that is not working, i.e. the pitch in LibrePilot will register when the yaw stick is moved, but yaw will now not register when pitch stick is moved. So to me this all points to the problem actually being with the "right stick up and down", and not the receiver or CC3D.

But, what is really weird to me is that when I again disconnect the FrSky DHT and reconnect the old 35MHz, then everything, including the "right stick up and down" works again!!!?????

So to me everything points to the FrSky DHT module to be the faulty item, but what I find very weird is that when it is installed, literally everything works except for the "right stick up and down", All of the other 5 channels work perfectly, which is just so weird to me.

Just to explain what the pitch actually does, when I try to configure it in LibrePilot, it does not register any movements I make with the "right stick up and down", but makes really random blips from the 50% (where it seems to be resting), to 100%, it does almost look like the random blips correspond with the blinking blue light when the CC3D is connected via usb, but after observing it for about 10min, I do not think this is the case.

I really hope someone can help me out, I really dont want to wait 2 months for a new transmitter.

Thanx in advance for anyone having gone through the effort of reading all of this.

Gerald
 
#2
Hi Gerald,

The problem may be as simple as the new receiver mapping the channels different from the JR. Disconnect everything but power from the receiver and connect a servo to each channel, one at a time and move the transmitter sticks one at a time and note which one moves the servo. Continue on until you have mapped your whole transmitter. Hopefully you will find the missing control on a blank channel Remember, a six channel transmitter will leave 2 unresponsive channels on an 8 channel receiver. In any event, good luck. I hope we can help get you sorted out quickly.

Mike
 

GeeSouth

Junior Member
#3
Hi Gerald,

The problem may be as simple as the new receiver mapping the channels different from the JR. Disconnect everything but power from the receiver and connect a servo to each channel, one at a time and move the transmitter sticks one at a time and note which one moves the servo. Continue on until you have mapped your whole transmitter. Hopefully you will find the missing control on a blank channel Remember, a six channel transmitter will leave 2 unresponsive channels on an 8 channel receiver. In any event, good luck. I hope we can help get you sorted out quickly.

Mike
Thanx for the advice Mike

I just tried your idea, it seems like all channels are assigned as they are supposed to, all of them are working except the pitch, it sits silently for about 8 seconds then makes a slight jitter, then sits still again for about 8 seconds and then makes a slight jitter, it does this whether I touch the stick or not, and when I do move the stick it doesnt register any movement other than the above mentioned jitter.
 
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pressalltheknobs

Posted a thousand or more times
#4
Its certainly worth trying all channels as mjmccarron suggests but the FrsKy DHT and RX is not going to re-order channels

...but it's possible this is the result of changing to mode2, I assume from mode 1. This switches THR to the right stick and ELV/PITCH to the left stick. Since ELV/PITCH is not working that change seems a likely cause.

JR to DHT is probably PPM which is necessarily ordered and the first 4 channels are likely the control channels in whatever order JR sends them. Changing the Mode will not change the intrinsic channel order of the TX system. I believe JR is TAER (Throttle, Ail(roll),Elv(Pitch),Rud(Yaw)

If the JR firmware allows you to remap sticks to channels then you might get ELV/PITCH as a different channel not in the first 4 but I doubt that's the case.

Since the FM module apparently works perhaps there is a different path the stick signals takes to the PPM out you used for the DHT hookup. I have to admit this seems a bit unlikely since I would expect them to get the same signal. What is more likely is that the pitch signal is somewhat degraded by a bad connection which means the FrSky TX is not getting a solid pulse for that channel but the pulse is sufficient for the FM transmitter which possibly re-enforces it - the FM TX probably essentially transmits the PPM signal

I would check for loose connections to do with the mode changed. You could have a bad connector and wires broken inside the insulation are not that uncommon. You may be able to diagnose something by wiggling wires but using a multi-meter to test for continuity and resistance might be better.
 

GeeSouth

Junior Member
#5
Its certainly worth trying all channels as mjmccarron suggests but the FrsKy DHT and RX is not going to re-order channels

...but it's possible this is the result of changing to mode2, I assume from mode 1. This switches THR to the right stick and ELV/PITCH to the left stick. Since ELV/PITCH is not working that change seems a likely cause.

JR to DHT is probably PPM which is necessarily ordered and the first 4 channels are likely the control channels in whatever order JR sends them. Changing the Mode will not change the intrinsic channel order of the TX system. I believe JR is TAER (Throttle, Ail(roll),Elv(Pitch),Rud(Yaw)

If the JR firmware allows you to remap sticks to channels then you might get ELV/PITCH as a different channel not in the first 4 but I doubt that's the case.

Since the FM module apparently works perhaps there is a different path the stick signals takes to the PPM out you used for the DHT hookup. I have to admit this seems a bit unlikely since I would expect them to get the same signal. What is more likely is that the pitch signal is somewhat degraded by a bad connection which means the FrSky TX is not getting a solid pulse for that channel but the pulse is sufficient for the FM transmitter which possibly re-enforces it - the FM TX probably essentially transmits the PPM signal

I would check for loose connections to do with the mode changed. You could have a bad connector and wires broken inside the insulation are not that uncommon. You may be able to diagnose something by wiggling wires but using a multi-meter to test for continuity and resistance might be better.
Hi pressalltheknobs

You are correct regarding the TAER channel assignment, even after the mode 2 conversion, it has stayed the same.

For the 35MHz to 2.3 conversion, I just took the +, - and signal wires (Red, Black & Yellow), which were the only wires that connect to the radio's fm transmitter board , and I hooked them up to the corresponding wires of the DHT, so there cant be a different path.
Also, when I converted to mode 2, the only hardware changes I made were to move the spring and ratchet plate from the old throttle stick to the new throttle stick, I didnt touch any of the electronics, all of that was handled within the software, I basically just went into the menu and changed the config from mode 1 to mode 2.

What you mentioned regarding the degraded or bad connection, that occurred to me aswell , I am currently busy checking around with my multi-meter, but havent found anything yet.

I think I am most affraid that the fault might be with the DHT, although it would be very strange that all other controls work perfectly, and only 1 is not.

In the end, the weak signal from the "right stick up and down" might be the most plausible, but I am having a bad time finding anything.
 
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pressalltheknobs

Posted a thousand or more times
#6
Hi pressalltheknobs


Also, when I converted to mode 2, the only hardware changes I made were to move the spring and ratchet plate from the old throttle stick to the new throttle stick, I didnt touch any of the electronics, all of that was handled within the software, I basically just went into the menu and changed the config from mode 1 to mode 2.
Hmm... my guess is that you have not completed the swap... There was nothing in the manual I found about it...
http://www.jramericas.com/manuals/JRP6812-manual.pdf

But check this out... sounds like it might be your problem

http://www.rcgroups.com/forums/showthread.php?t=1047909

also discussed here

http://www.rcgroups.com/forums/showthread.php?t=1508393
 

GeeSouth

Junior Member
#7
Hmm... my guess is that you have not completed the swap... There was nothing in the manual I found about it...
http://www.jramericas.com/manuals/JRP6812-manual.pdf

But check this out... sounds like it might be your problem

http://www.rcgroups.com/forums/showthread.php?t=1047909

also discussed here

http://www.rcgroups.com/forums/showthread.php?t=1508393
Thanx, Ill check those links now.
The mode switch within the settings is not mentioned in the manual, I found the deep settings menu, when you hold the scroll and increase buttons and then switch the tx on while they are pressed, as you scroll through, you get to a mode setting where you can choose 1 or 2, and as I say, this has been working perfectly on 35MHz.

Interesting revelation though, If I change back to mode 1, then it is the "Left stick up and down" that does not register. i.e. it seems like it is channel 3 that is the problem.
This is making me question the receiver again.
 

GeeSouth

Junior Member
#8
Thanx, Ill check those links now.
The mode switch within the settings is not mentioned in the manual, I found the deep settings menu, when you hold the scroll and increase buttons and then switch the tx on while they are pressed, as you scroll through, you get to a mode setting where you can choose 1 or 2, and as I say, this has been working perfectly on 35MHz.

Interesting revelation though, If I change back to mode 1, then it is the "Left stick up and down" that does not register. i.e. it seems like it is channel 3 that is the problem.
This is making me question the receiver again.
The method I used is mentioned in the second to last post (#13) in the second link.
http://www.rcgroups.com/forums/showthread.php?t=1508393
 

pressalltheknobs

Posted a thousand or more times
#10
ok then no jumpers...

I looked at the video linked in that reddit post
https://www.youtube.com/watch?v=FcZlXd3d7O4&feature=youtu.be

It was CH4 in his case...hmmm

Yeah, does look like it might be the receiver.

Well just FYI while poking around I came across this link which may be of interest. Possibly you need to flash the RX with latest firmware. Something to keep in mind anyway.
https://nathan.vertile.com/blog/2016/02/09/airwolf-diy-frsky-rx-sbus/#top

I think there was a blog link entry associated with doing that in the reviews of it...
http://www.banggood.com/DIY-FRSKY-8...-DFT-DHT-p-987247.html?p=1G09211226617201502J
Might have been on the 802 I saw it


I also saw this comment...

"works fine with Transmitters sending 8 Channels like Taranis in D8 Mode. Testet in Graupner MC10/12 with DHT Modul and in Taranis with DJT Modul transmitting only 7 Channels then Output on Channel 3 is allways Failsafe (ca 1000us) other Channels will work normal."

so that could be an issue.
 
#12
ok then no jumpers...

I looked at the video linked in that reddit post
https://www.youtube.com/watch?v=FcZlXd3d7O4&feature=youtu.be

It was CH4 in his case...hmmm

Yeah, does look like it might be the receiver.

Well just FYI while poking around I came across this link which may be of interest. Possibly you need to flash the RX with latest firmware. Something to keep in mind anyway.
https://nathan.vertile.com/blog/2016/02/09/airwolf-diy-frsky-rx-sbus/#top

I think there was a blog link entry associated with doing that in the reviews of it...
http://www.banggood.com/DIY-FRSKY-8...-DFT-DHT-p-987247.html?p=1G09211226617201502J
Might have been on the 802 I saw it


I also saw this comment...

"works fine with Transmitters sending 8 Channels like Taranis in D8 Mode. Testet in Graupner MC10/12 with DHT Modul and in Taranis with DJT Modul transmitting only 7 Channels then Output on Channel 3 is allways Failsafe (ca 1000us) other Channels will work normal."

so that could be an issue.
Wow, thanx man, I really appreciate you trying so hard to help me out here.
Ill follow up on those posts and get back.
 
#13
Okay, just to let you guys know where I am at now.

It would seem like the problem lies with the receiver.
It might be something to do with the fact that there is a failsafe on channel 3, but I cannot be sure.

Anyway.
I have found a workaround, I am now using it in PPM mode off of its channel 4 pins.
For this it requires you to bridge the channel 1 & 3 signal pins.

So, this works perfectly, I now have it registering all 6 channels from the TX.

All I need to do now is flash the ESC's with BLHeli for OneShot.

Thanx for all the help.