Grounding to Rx (FrSky D8R-XP) of on board glow device

Cant get your radio to work? General Hardware issues?
Post Reply
User avatar
Nadim
Posts: 52
Joined: Tue Feb 23, 2016 11:42 am
Country: -

Grounding to Rx (FrSky D8R-XP) of on board glow device

Post by Nadim » Tue Jul 10, 2018 6:16 am

Hi there,

I am about to install an On Board Glow device to my D8R-XP (pretty much the same as D8R-II plus, for those who aren't familiar with this Rx).

The OBG can be powered via Rx or with a separate battery, and this (PIC 1) is what the manual says about both configurations.
PIC 1.jpg
Disclaimer: I know nothing about electronics

Now, what I'd rather do is (PIC 2).
PIC 2.jpg
The question is: do I need to reconnect the black wire from the battery to the Rx? This is probably a dumb question for anyone with an ABC in electronics, but as I said above, I know absolutely zero: red is positive, black is negative, and stop. :lol:

I guess my setup would count as a single battery setup BUT there is a BEC in the way that may or may not change things in terms of grounding.

I hope my pictures are understandable.
Thank you guys. :)

EDIT: I ask this because if it's just the signal wire I've to connect from the OBG to the Rx, then no problem, but if it's also the black wire, that would be a problem since currently I don't have any empty channel slot left...

User avatar
jhsa
Posts: 17812
Joined: Tue Dec 27, 2011 5:13 pm
Country: Germany

Re: Grounding to Rx (FrSky D8R-XP) of on board glow device

Post by jhsa » Tue Jul 10, 2018 8:12 am

You can connect exactly as shpwn in Pic2. The receiver receives the ground from the BEC. The Glow Driver receives the ground directly from the battery. So, only the signal wire needed from the Glow Driver to the Battery, exactly as in the picture. This way, ground loops are avoided.

If you need to connect another wire to a channel that is already busy, use a "Y" cable.. Simple.

I personaly don't like a single battery setup, but that is just my preference. :)

João
My er9x/Ersky9x/eepskye Video Tutorials
https://www.youtube.com/playlist?list=PL5uJhoD7sAKidZmkhMpYpp_qcuIqJXhb9

Donate to Er9x/Ersky9x:
https://www.paypal.com/cgi-bin/webscr?cmd=_s-xclick&hosted_button_id=YHX43JR3J7XGW

User avatar
Kilrah
Posts: 9515
Joined: Sat Feb 18, 2012 6:56 pm
Country: Switzerland

Re: Grounding to Rx (FrSky D8R-XP) of on board glow device

Post by Kilrah » Tue Jul 10, 2018 8:13 am

No additional ground, that goes through the BEC already.

But check your glow driver's documentation, it might not support a 2s lipo on its input.

User avatar
Nadim
Posts: 52
Joined: Tue Feb 23, 2016 11:42 am
Country: -

Re: Grounding to Rx (FrSky D8R-XP) of on board glow device

Post by Nadim » Tue Jul 10, 2018 8:32 am

Thanks guys. :)
jhsa wrote:
Tue Jul 10, 2018 8:12 am
You can connect exactly as shpwn in Pic2. The receiver receives the ground from the BEC. The Glow Driver receives the ground directly from the battery. So, only the signal wire needed from the Glow Driver to the Battery, exactly as in the picture. This way, ground loops are avoided.
That's what I sort of imagined to be the case, but... doesn't this bring up the question as to why, in the two batteries setup from the manual, there is an additional ground going from battery 2 to the Rx? The receiver should be already receiving ground from its own battery, and the OBG driver from its own, in turn. This is actually the part that took me aback while reading the manual...
jhsa wrote:
Tue Jul 10, 2018 8:12 am
If you need to connect another wire to a channel that is already busy, use a "Y" cable.. Simple.
Yes of course it could be done in theory but I have literally no space inside of the plane (already fitting this OBG is going to be a challenge), and I don't want further mess with wires and derivations. Connecting only the signal wire from the glow driver is going to be fine because I will physically put it in the connector coming from the BEC to the Rx, which, of course, only has black & red wires. This is the neates installation I was hoping for. :D

@Kilrah: yes, the manual says the glow driver takes from 4,5V up to 16V. I've already tested it with a 2S lipo and it works fine. Actually the manual states it is even better to feed it with more than the canonical 5-6V from the Rx. I guess they were thinking of unregulated NiCd or NiMh, subject to voltage drops under load, which would potentially shut off the driver. But with a BEC set to 6V, I don't think the voltage will ever get that low... So far I've been using the Rx internal sensor to check it and it really stays pretty much around 6V. In fact, I would have connected the glow driver to the Rx directly if I hadn't had the abovementioned problem of no spare channels...

Thanks again. ;)

User avatar
jhsa
Posts: 17812
Joined: Tue Dec 27, 2011 5:13 pm
Country: Germany

Re: Grounding to Rx (FrSky D8R-XP) of on board glow device

Post by jhsa » Tue Jul 10, 2018 8:43 am

The voltage drops under load could shut off your receiver, and that would be your real problem. ;) And that is the reason why I prefer the 2 batteries setup :)

About the grounds. On the 2 battery setup the batteries grounds are not connected together. As you can see, the glow battery connects only to the driver, and the other only to the receiver. That is why you also need a ground wire from the driver to the receiver..

João
My er9x/Ersky9x/eepskye Video Tutorials
https://www.youtube.com/playlist?list=PL5uJhoD7sAKidZmkhMpYpp_qcuIqJXhb9

Donate to Er9x/Ersky9x:
https://www.paypal.com/cgi-bin/webscr?cmd=_s-xclick&hosted_button_id=YHX43JR3J7XGW


User avatar
Nadim
Posts: 52
Joined: Tue Feb 23, 2016 11:42 am
Country: -

Re: Grounding to Rx (FrSky D8R-XP) of on board glow device

Post by Nadim » Tue Jul 10, 2018 8:51 am

jhsa wrote:
Tue Jul 10, 2018 8:43 am
The voltage drops under load could shut off your receiver, and that would be your real problem. ;) And that is the reason why I prefer the 2 batteries setup :)
Yes but having the Rx dead for one second and then back to life again is still way better than having the engine shutting off... and NOT back to life again. :o

I'm not seeing how, however, going 2-batteries, per se, can eliminate the Rx brownout problem. Most Rxs are probably rated to work for 4,8 V as a minimum, and I don't see how 6 volts coming from the BEC (which in turns is feeded by a 2S) can suddenly drop below 4,8V.

But even if they did, I still don't see how having 2 batteries would solve this. Of course you spare more amps/h with two batteries and they will last longer, but to me, that's just another battery to check and replace between flights...
jhsa wrote:
Tue Jul 10, 2018 8:43 am
About the grounds. On the 2 battery setup the batteries grounds are not connected together.
Hah! I see... As I said, electronics is not my field of expertise really. :D

User avatar
Kilrah
Posts: 9515
Joined: Sat Feb 18, 2012 6:56 pm
Country: Switzerland

Re: Grounding to Rx (FrSky D8R-XP) of on board glow device

Post by Kilrah » Tue Jul 10, 2018 9:49 am

Nadim wrote:
Tue Jul 10, 2018 8:51 am
But even if they did, I still don't see how having 2 batteries would solve this. Of course you spare more amps/h with two batteries and they will last longer, but to me, that's just another battery to check and replace between flights...
Because with 2 batteries your glow battery could be empty/dead/overloaded and it wouldn't matter to the receiver and RC. With a single battery, a non-essential system can bring down an essential one.
Just be aware of it...

User avatar
jhsa
Posts: 17812
Joined: Tue Dec 27, 2011 5:13 pm
Country: Germany

Re: Grounding to Rx (FrSky D8R-XP) of on board glow device

Post by jhsa » Tue Jul 10, 2018 9:59 am

Nadim wrote:
Tue Jul 10, 2018 8:51 am


Yes but having the Rx dead for one second and then back to life again is still way better than having the engine shutting off... and NOT back to life again. :o
I wouldn't count on it.. even if the brownout would last only one second (which it doesn't believe me, been there :) ) it is time enough to throw your pride and joy to the ground with no control, and smash it to pieces. :o :shock:
I would rather have the engine stopping and still have control, than a model without control at full throttle.
and having no glow driver doesn't necessarily mean that the engine will stop. the glow plug is kept hot by the combustion. I use the onboard glow to start the model's engine without wires connecting to it as they can get caught by the prop. And then configure my radio to only turn the glow ON at idle.. above about one quarter of the stick movement, it shuts OFF. This depends on the engine, fuel, and glow plug used of course.. :)
But trust me, something you do not want is a receiver brownout with an engine running ;) :D

If the single battery is a LiPo battery, there is less chance of this happening than with NiCd or NiMh, but still.

I'm not seeing how, however, going 2-batteries, per se, can eliminate the Rx brownout problem
.

The answer is in the pictures you've posted ;) On the 2 battery setup, one battery powers the receiver and servos ONLY, and the other powers the Glow Driver ONLY.
Most Rxs are probably rated to work for 4,8 V as a minimum, and I don't see how 6 volts coming from the BEC (which in turns is feeded by a 2S) can suddenly drop below 4,8V.
For a BEC to deliver reliable 6V, and depending on the BEC, it needs to be fed with some higher voltage. Let's see the best situation here. A 2 cell Lipo Battery is considered empty at about 3V per cell, and this is already too low. this makes 6V, and it is already too low for the BEC. Ahh, and don't forget that your servos are also loading the battery. on a normal sized model with 5 or 6 standard sized servos you can expect probably between 2 and 3 Amps of current peak. that is what i measured on one of my models when i was selecting a BEC for it..
So, if the battery voltage drops to 6V the BEC won't be delivering 6V anymore, it will be less, and it will get worse every time you move a servo or the glow driver turns ON.
Even at 6.6V (3.3V per cell), it might be already to low and the battery should never be drained that low anyway.
Of course, if using the old Nicd and Nimh batteries, this setup would even be unthinkable as the voltage drop on these batteries is very bad compared to the LiPos.

So, my advice is, if you are going to use the single battery setup, make sure you have telemetry and a good voltage sensor on your model. set the alarm quite high, well above 7V. Use a higher capacity LiPo with a larger C rating. This could minimize voltage drops.. You really do not want these :)

I have built my own Glow drivers that together with the openXsensor (open source multi sensor board) reports also a broken glow plug :)
This reminds me that I have actually to finish this plane :mrgreen: :mrgreen:
But even if they did, I still don't see how having 2 batteries would solve this. Of course you spare more amps/h with two batteries and they will last longer, but to me, that's just another battery to check and replace between flights...
Better checking the batteries between flights anyway, even if it is just a single battery. Safety above all :) Or, as I suggested above, telemetry.. Which radio do you have?

João
My er9x/Ersky9x/eepskye Video Tutorials
https://www.youtube.com/playlist?list=PL5uJhoD7sAKidZmkhMpYpp_qcuIqJXhb9

Donate to Er9x/Ersky9x:
https://www.paypal.com/cgi-bin/webscr?cmd=_s-xclick&hosted_button_id=YHX43JR3J7XGW

User avatar
Nadim
Posts: 52
Joined: Tue Feb 23, 2016 11:42 am
Country: -

Re: Grounding to Rx (FrSky D8R-XP) of on board glow device

Post by Nadim » Tue Jul 10, 2018 11:05 am

When I said I don't understand a thing about Electronics, I'm afraid I gave the impression of not being much attentive to safety and these kind of things.
While the first one is absolutely true, I AM definitely paranoid when it comes to setting things up and I have quite a lot of fun programming in things in my radio. :D

I've been using OpenTX (first on a 9x, now on a Taranis) for about 4 years or so and I've never flown anything without a voltage sensor and telemetry alarms linked to it. I'm referring to both the battery voltage and the BEC internal voltage. I set my alarms in a very conservative way too. The resting voltage of my lipos are usually at around 3,7 or 3,8 volts when I finish flying, so basically ready to be stored. :lol:

I've always opted for single battery setup. I'm not saying this is better, I just think that, if used with care (see the above), it can work as well in my opinion.

So far I've never had a crash because of the above. Not that it couldn't happen, but I try to minimize the likelihood... as we all do.
jhsa wrote:
Tue Jul 10, 2018 9:59 am
I would rather have the engine stopping and still have control, than a model without control at full throttle.
and having no glow driver doesn't necessarily mean that the engine will stop. the glow plug is kept hot by the combustion. I use the onboard glow to start the model's engine without wires connecting to it as they can get caught by the prop. And then configure my radio to only turn the glow ON at idle.. above about one quarter of the stick movement, it shuts OFF. This depends on the engine, fuel, and glow plug used of course.. :)
Yeah I hadn't mentioned this because that would have turned out long and most definitely go OT, but, in my specific case, an engine dying isn't a fun scenario either. Of course it's better than totally losing the plane, but it's an aerobatic plane with, really, little gliding capabilities, so a throttle deadstick would mean pretty much some serious damage (experience :roll: :D). Plus the reason why I want to install an OBG is because of the fairly rich mixture I'm using on the LS needle, which now forces me to keep a high idle RPM to prevent flooding. With an OBG, my hope is to lower idle RPM more and have a smooth idle in general, while keeping the mixture on the rich side. I already tried playing with the glow ingniter while adjusting idle and it does help immensely, so that's why I'm pretty sure it will work. "Just tune your engine better"... THIS is why I wasn't mentioning the above, I don't want to get into the weeds of tuning arguments...

As for the OBG settings, what I programmed in so far inside OpenTX is glow fully on with throttle between zero and 20%, then, glow reduced to 50% with throttle between 20% and 40%, and then off from 40% on. We'll see how it works! The nice think I didn't know about this on board glow driver is precisely this, that it can interpret a 50% signal from the Rx as "half heat on the plug". I had expected it to be just on/off, but it's a nice surprise.
jhsa wrote:
Tue Jul 10, 2018 9:59 am
I'm not seeing how, however, going 2-batteries, per se, can eliminate the Rx brownout problem
.

The answer is in the pictures you've posted ;) On the 2 battery setup, one battery powers the receiver and servos ONLY, and the other powers the Glow Driver ONLY.
Of course the two are powered separately and in case of failure of one battery, the other one will keep going, but in my case ONE battery which keeps going doesn't mean the plane being safer. Let's me break this down:

1) Single battery: in case of failure, everything will be lost. Plane either flying to the horizon until the fuel burns off or diving into the ground. Probably the second one is 99.9999 % more likely to happen much before the first one could ever happen. Not nice.

2) Double battery: failure of the Rx battery: same as above. Failure of the OBG battery: engine dying at the first maneuver I do and plane smashing into the ground. Not nice.

So while I do see the arguments in favour ot two batteries, in my specific case, either one that fails, it would mean losing the plane. Thus I don't see how a double battery setup would be saf"er". In fact, it could increase the risk of failure, while adding battery weight and another voltage sensor... another voltage alarm to worry about. So I keep saying: with my particular needs, a single battery seems to work best for me.

Seen differently, just because a new source of amps (that is, the OBG) is being connected to the main (and only) battery, it doesn't mean the battery is more prone to fail - unless the OBG driver screws things up. Possible, I guess... but see all the above.
jhsa wrote:
Tue Jul 10, 2018 9:59 am
For a BEC to deliver reliable 6V, and depending on the BEC, it needs to be fed with some higher voltage. Let's see the best situation here. A 2 cell Lipo Battery is considered empty at about 3V per cell, and this is already too low. this makes 6V, and it is already too low for the BEC. Ahh, and don't forget that your servos are also loading the battery. on a normal sized model with 5 or 6 standard sized servos you can expect probably between 2 and 3 Amps of current peak. that is what i measured on one of my models when i was selecting a BEC for it..
So, if the battery voltage drops to 6V the BEC won't be delivering 6V anymore, it will be less, and it will get worse every time you move a servo or the glow driver turns ON.
I've always used two separated alarms for the battery main voltage and for the internal voltage of the BEC. While the main voltage does drop quite noticeably when flying, I've yet to see an internal BEC voltage to drop more than 0,5 V even in the most extremes of the maneuvers (...that I can do :mrgreen: ). Of course I am talking here with a fully charged battery. But as I said, I don't fly when the cells are below 3,7, so...
jhsa wrote:
Tue Jul 10, 2018 9:59 am
I have built my own Glow drivers that together with the openXsensor (open source multi sensor board) reports also a broken glow plug :)
This reminds me that I have actually to finish this plane :mrgreen: :mrgreen:
This is nice! :) Actually this OBG driver, too, says it indicates with a LED flashing when the plug is broken. I've yet to get used to what all the LED combinations mean, but that's a nice feature to have.
jhsa wrote:
Tue Jul 10, 2018 9:59 am
Better checking the batteries between flights anyway, even if it is just a single battery. Safety above all :) Or, as I suggested above, telemetry.. Which radio do you have?
My usual priorities: safety > weight > price :mrgreen: :mrgreen:

Thanks guys! I'm going to install this thing soon.

User avatar
jhsa
Posts: 17812
Joined: Tue Dec 27, 2011 5:13 pm
Country: Germany

Re: Grounding to Rx (FrSky D8R-XP) of on board glow device

Post by jhsa » Tue Jul 10, 2018 2:23 pm

Good luck :) As long as we have fun safely, that is what matters!! ;) :D

João
My er9x/Ersky9x/eepskye Video Tutorials
https://www.youtube.com/playlist?list=PL5uJhoD7sAKidZmkhMpYpp_qcuIqJXhb9

Donate to Er9x/Ersky9x:
https://www.paypal.com/cgi-bin/webscr?cmd=_s-xclick&hosted_button_id=YHX43JR3J7XGW

Post Reply

Return to “Hardware”