DragonOSD+V2 with RTH - Page 888 - RC Groups
Sep 06, 2011, 10:27 PM
Registered User
I have a few diagrams which shows where the ground comes from.

So which is the correct one?

DOSD Wiring Vtx and Cam to DOSD
DOSD Wiring Lipo to DOSD
DOSD Wiring Cam to DOSD
DOSD Wiring Vtx to DOSD

### Images

Sep 06, 2011, 10:44 PM
'FPV'er...not a "LOS'er
Quote:
 Originally Posted by roypwee It seems that many people have the same problem as mine. Still trying to figure out from Ren's simplified diagram previously. Where do we get the ground from to the Video Input on the DOSD? From Camera to GND of the Video DOSD? (Additional GND Wire from Camera out to Video DOSD) or From VTx to GND of the Video DOSD? (Additional GND Wire from VTx out to Video DOSD) or Ground comes directly from Lipo to GND of the Video DOSD? As I am powering the VTx and Camera from a separate battery source. Or if it is from the same battery source?
Yeah, it can really get confusing. Since all your electronics have to work with each other they MUST have a common reference...the ground. If you don't, the different electronics can have a hard time communicating with each other. Take this quicky example:
To find my house, go north 1 mile, turn left, then your second right, my house is on the left. So, can you find where I live with that? No. Why? Because we have no common reference with each other. Now let's do this with a common reference. From the corner of 1st and A street, go north 1 mile, turn left, then your second right, my house is on the left. The chance of you understanding and finding me is significantly improved...unless you're my wife, she can't find her way out of a parking lot...that's a different story though... Electronics don't communicate verbally, but via changing voltage levels. If they don't understand each other's voltage level they might not 'understand' the signal being sent.

Now, where do we make this common ground point? That kinda really doesn't matter. Most electronics circuit boards use a common ground plane, i.e. all the ground connections essentially connect to each other. As long as the negative lead on your two batteries connect to this ground plane they now have a common reference and will understand each other's signals. Each piece of electronics must connect to this ground plane to operate properly. If a gnd from one piece of electronics connect to both the direct ground as well as another piece of equipment that then connects to the direct ground then you have a ground loop, i.e. the current can pass both directly to the ground plane as well as thru the second piece of equipment and then to the ground plane. This is where issues can occur.

Now, if each separate piece of equipment connected to the exact same spot then no ground loops are created as the current through each component can ONLY flow to a common point, not through anything else. Does any of that help? Yeah, it can be confusing and I am an electronic repair tech and still get confused.

Here's a quickly little article you can look at too: http://fpv-japan.com/technical-info/...issue/lang/en/ .
Sep 06, 2011, 10:50 PM
Registered User
Quote:
 Originally Posted by Vantasstic Yeah, it can really get confusing. Since all your electronics have to work with each other they MUST have a common reference...the ground. If you don't, the different electronics can have a hard time communicating with each other. Take this quicky example: To find my house, go north 1 mile, turn left, then your second right, my house is on the left. So, can you find where I live with that? No. Why? Because we have no common reference with each other. Now let's do this with a common reference. From the corner of 1st and A street, go north 1 mile, turn left, then your second right, my house is on the left. The chance of you understanding and finding me is significantly improved...unless you're my wife, she can't find her way out of a parking lot...that's a different story though... Electronics don't communicate verbally, but via changing voltage levels. If they don't understand each other's voltage level they might not 'understand' the signal being sent. Now, where do we make this common ground point? That kinda really doesn't matter. Most electronics circuit boards use a common ground plane, i.e. all the ground connections essentially connect to each other. As long as the negative lead on your two batteries connect to this ground plane they now have a common reference and will understand each other's signals. Each piece of electronics must connect to this ground plane to operate properly. If a gnd from one piece of electronics connect to both the direct ground as well as another piece of equipment that then connects to the direct ground then you have a ground loop, i.e. the current can pass both directly to the ground plane as well as thru the second piece of equipment and then to the ground plane. This is where issues can occur. Now, if each separate piece of equipment connected to the exact same spot then no ground loops are created as the current through each component can ONLY flow to a common point, not through anything else. Does any of that help? Yeah, it can be confusing and I am an electronic repair tech and still get confused. Here's a quickly little article you can look at too: http://fpv-japan.com/technical-info/...issue/lang/en/ .
Isnt there a risk of high current flowing through wires/components that would be damaged by it when everything is sharing a ground? I.e. couldnt the high amps my motor pulls return through components that cant handle it? Or is this only the case when you have a ground loop?

Sorry if what I just said made no sense
Sep 06, 2011, 11:04 PM
'FPV'er...not a "LOS'er
Quote:
 Originally Posted by roypwee I have a few diagrams which shows where the ground comes from. So which is the correct one? DOSD Wiring Vtx and Cam to DOSD DOSD Wiring Lipo to DOSD DOSD Wiring Cam to DOSD DOSD Wiring Vtx to DOSD
Figure 2 would be the most correct. In figures 1, 3, and 4 have ground loops, i.e. you have a ground line that connects the video components to BOTH the negative terminal on the battery AND to the video GND pin. In actuality, figure #2 has an extra ground lead (from the battery negative terminal to the video GND terminal). This isn't really a loop as the battery gnd and video ground are already connected to the ground plane in the circuit board...thus just a redundant connection. IMHO, these such 'loops' shouldn't be critical as they're low current devices. Where most have problems is a ground loop in the high current section of between the flight battery and speed control. To avoid this high current loop you need to only connect the main +/- battery wires to the ESC, then the ONLY the Signal wire from the ESC to the DOSD/Rx. Now the only place the high current flow path is to the main battery lines. If you connect the ESC servo lead negative wire then current can flow directly to the main battery lead AND back through your DOSD/Rx, then though whatever other components it takes to lead back to the 'main ground'. This high current leads to higher temperatures in wires/components not designed for that current, thus over heat and burn up.

Last thing...The reason I said connect only the Signal wire from the ESC is because I'd recommend using a Switch Mode External BEC to power your electronics (Rx, servos) with. If you're going to use the speed control's internal BEC then you want to connect ONLY the + and Signal leads and leave the negative lead not connected.
Sep 06, 2011, 11:09 PM
Registered User
Thanks Fantastic... I know the misspelled name....

So its figure 2.

Yes I do have a CC 10AMP BEC to power the Rx and Servos.

Quote:
 Originally Posted by Vantasstic Figure 2 would be the most correct. In figures 1, 3, and 4 have ground loops, i.e. you have a ground line that connects the video components to BOTH the negative terminal on the battery AND to the video GND pin. In actuality, figure #2 has an extra ground lead (from the battery negative terminal to the video GND terminal). This isn't really a loop as the battery gnd and video ground are already connected to the ground plane in the circuit board...thus just a redundant connection. IMHO, these such 'loops' shouldn't be critical as they're low current devices. Where most have problems is a ground loop in the high current section of between the flight battery and speed control. To avoid this high current loop you need to only connect the main +/- battery wires to the ESC, then the ONLY the Signal wire from the ESC to the DOSD/Rx. Now the only place the high current flow path is to the main battery lines. If you connect the ESC servo lead negative wire then current can flow directly to the main battery lead AND back through your DOSD/Rx, then though whatever other components it takes to lead back to the 'main ground'. This high current leads to higher temperatures in wires/components not designed for that current, thus over heat and burn up. Last thing...The reason I said connect only the Signal wire from the ESC is because I'd recommend using a Switch Mode External BEC to power your electronics (Rx, servos) with. If you're going to use the speed control's internal BEC then you want to connect ONLY the + and Signal leads and leave the negative lead not connected.
Sep 06, 2011, 11:16 PM
'FPV'er...not a "LOS'er
Quote:
 Originally Posted by JLager Isnt there a risk of high current flowing through wires/components that would be damaged by it when everything is sharing a ground? I.e. couldnt the high amps my motor pulls return through components that cant handle it? Or is this only the case when you have a ground loop? Sorry if what I just said made no sense
The concern is flowing high currents through something not designed for high current. Take a look at your battery wires...pretty thick eh? Not take a look at the servo lead type wires. Pretty thin eh? With currently only being able to pass through the thick, heavy duty, designed to handle lots of current, wiring then all is happy. Now try to pass some, a lot, nearly all of that high current through those small little wires...now you've got problems.

Okay, another example. Sorry, I love examples. The main highway through your town is designed to flow lots of cars at high speed without problem (wider roads, no stop signs, etc). Since this is the ONLY place the traffic can flow no problems occur. Now take that same highway traffic and funnel it onto a one lane side street, through a school zone, with lots of dips and pot holes in the way. The traffic flow is going to jam up and people get pissed, and tempers get hot, and you have a road rage melt down...not good and no one is happy, Now some architect flunky designed the highway so three lanes of traffic can go down the highway, but one lane of that highway traffic HAS TO take that one-lane side street with all the same obstacles and then connects it back to the major highway five miles down the road...(the 'ground loop). While most of the traffic 'flows' down the major highway just fine, some of that traffic gets bundled up, bottle necked, heated up, yet has no choice to go anywhere else because of all the cars behind it just pushing it along...like it or not. The one lane traffic overheats, breaks down, etc.
Sep 06, 2011, 11:26 PM
'FPV'er...not a "LOS'er
Quote:
 Originally Posted by roypwee Thanks Fantastic... I know the misspelled name.... So its figure 2. Yes I do have a CC 10AMP BEC to power the Rx and Servos.
I'd say figure 2 without the wire between the battery ground and video ground.

With all that said, that's not how I have my system connected. I have my camera, VTx, and DOSD video GND pin connected to each other. My video flight pack + and - wires connect to the DOSD power input pins. My video equipment + lead connect into the video battery + line. I don't recall if my video equipment GND pins also connect to the video battery ground or not...I'd have to double check. If so, then, Yes, I have a ground loop. It's a low current ground loop and not so critical and hasn't caused me any issues. The one thing I did make sure to do was only connect the Signal wire from my ESC servo leads to the DOSD.
Sep 06, 2011, 11:37 PM
Registered User
"I have my camera, VTx, and DOSD video GND pin connected to each other."

You mean like this? or care amend this diagram?

Cheers.

Quote:
 Originally Posted by Vantasstic I'd say figure 2 without the wire between the battery ground and video ground. With all that said, that's not how I have my system connected. I have my camera, VTx, and DOSD video GND pin connected to each other. My video flight pack + and - wires connect to the DOSD power input pins. My video equipment + lead connect into the video battery + line. I don't recall if my video equipment GND pins also connect to the video battery ground or not...I'd have to double check. If so, then, Yes, I have a ground loop. It's a low current ground loop and not so critical and hasn't caused me any issues. The one thing I did make sure to do was only connect the Signal wire from my ESC servo leads to the DOSD.

### Images

Sep 06, 2011, 11:48 PM
Registered User
Quote:
 Originally Posted by Vantasstic The concern is flowing high currents through something not designed for high current. Take a look at your battery wires...pretty thick eh? Not take a look at the servo lead type wires. Pretty thin eh? With currently only being able to pass through the thick, heavy duty, designed to handle lots of current, wiring then all is happy. Now try to pass some, a lot, nearly all of that high current through those small little wires...now you've got problems. Okay, another example. Sorry, I love examples. The main highway through your town is designed to flow lots of cars at high speed without problem (wider roads, no stop signs, etc). Since this is the ONLY place the traffic can flow no problems occur. Now take that same highway traffic and funnel it onto a one lane side street, through a school zone, with lots of dips and pot holes in the way. The traffic flow is going to jam up and people get pissed, and tempers get hot, and you have a road rage melt down...not good and no one is happy, Now some architect flunky designed the highway so three lanes of traffic can go down the highway, but one lane of that highway traffic HAS TO take that one-lane side street with all the same obstacles and then connects it back to the major highway five miles down the road...(the 'ground loop). While most of the traffic 'flows' down the major highway just fine, some of that traffic gets bundled up, bottle necked, heated up, yet has no choice to go anywhere else because of all the cars behind it just pushing it along...like it or not. The one lane traffic overheats, breaks down, etc.
Thanks for the detailed example I get that high current through thin wires = bad. I still find it hard to figure out if that has the potential to happen in my wiring though. Wired up like the attached diagram, can I cause a dangerous ground loop or not?

### Images

 Sep 07, 2011, 12:10 AM Registered User Thanks a lot for your response, My settings are as follows, AP Rotgain 68.00 Rot limit 30.00 Rot step gain 6.00 Max heading chg 45 deg AP Rocgain 50.00 Roc limit 10.00 Roc stepgain 6.00 Max alt chg. 10.00m Low speed limit 20.60 kph Cruise speed 32.00 kph Cruise alt. 150m Decsent mode 1 Throttle step 2 Auto stabilization gain 0.000 Gps stabilization gain 0.000 Altitude limit 30.000 Hit distance 200m Current waypoint 0 Waypoint mode visit The only thing i have connected to the osd in addition to gps, current sensor and rssi is ppm channel 9 which is going to channel 9 of the Dlink. I have nothing connected to the pwm outputs. So if your refering to controlling any channels with the osd I don't think I am. Could that be the problem. I do have Ailerons, elevator, rudder and throttle connected to rx and i am powering the osd with the current monitor and and rx thru the speed controllers bec. I assume the ppm is sending the 5 volts to the osd. I'm also powering video with seperate 12 v battery. Is this enough info? Thanks, Dennis
Sep 07, 2011, 12:12 AM
Air Crash Expert
That drawing looks vaguely familiar.
#1 one has a loop shown with green arrows.
The key thing to keep in mind, is that each component should have only one ground wire to it. The exception is the DOSD board. It has a main ground next to the main power pin and it also has a servo rail ground, which feeds only the PWM's and PPM.
In figure #1, the Vtx and camera each have two, forming a loop.

And before anyone says it....yes, my original drawing shows two grounds to the camera. It's a Sony board cam and the ground had to be connected to the GND pin next to the video pin on the OSD in order for it to work. Please don't ask why, it just did.

ETA: I've never had high current draw through any component (other than a motor or ESC) unless it was shorted...in which case it matters not how you have it wired.

### Images

 Sep 07, 2011, 12:13 AM Registered User Thanks a lot Dennis
Sep 07, 2011, 12:17 AM
Air Crash Expert
Quote:
 Originally Posted by mrdaction I have nothing connected to the pwm outputs. So if your refering to controlling any channels with the osd I don't think I am. Could that be the problem. I do have Ailerons, elevator, rudder and throttle connected to rx and i am powering the osd with the current monitor and and rx thru the speed controllers bec. I assume the ppm is sending the 5 volts to the osd. I'm also powering video with seperate 12 v battery. Is this enough info? Thanks, Dennis
Uh, the AP is part of the DOSD...if your not driving servos with the DOSD, then your not using AP. You really need to read the manual.
Sep 07, 2011, 01:17 AM
Team Basement-RC
Quote:
 Originally Posted by mrdaction Thanks a lot for your response, My settings are as follows, AP Rotgain 68.00 Rot limit 30.00 Rot step gain 6.00 Max heading chg 45 deg AP Rocgain 50.00 Roc limit 10.00 Roc stepgain 6.00 Max alt chg. 10.00m Low speed limit 20.60 kph Cruise speed 32.00 kph Cruise alt. 150m Decsent mode 1 Throttle step 2 Auto stabilization gain 0.000 Gps stabilization gain 0.000 Altitude limit 30.000 Hit distance 200m Current waypoint 0 Waypoint mode visit The only thing i have connected to the osd in addition to gps, current sensor and rssi is ppm channel 9 which is going to channel 9 of the Dlink. I have nothing connected to the pwm outputs. So if your refering to controlling any channels with the osd I don't think I am. Could that be the problem. I do have Ailerons, elevator, rudder and throttle connected to rx and i am powering the osd with the current monitor and and rx thru the speed controllers bec. I assume the ppm is sending the 5 volts to the osd. I'm also powering video with seperate 12 v battery. Is this enough info? Thanks, Dennis
That's definitely the problem. Your servos have to be plugged into the DOSD. All you need plugged into the receiver is ppm on channel 9 and the rssi connection.
Sep 07, 2011, 09:32 AM
'FPV'er...not a "LOS'er
Quote:
 Originally Posted by JLager Thanks for the detailed example I get that high current through thin wires = bad. I still find it hard to figure out if that has the potential to happen in my wiring though. Wired up like the attached diagram, can I cause a dangerous ground loop or not?
The drawing you did looks fine, I don't see any special issues. At most, the output of the DOSD PWM to the FY-20 could be done with one single +,-,S wire on one of the PWM connectors and the other ports could just be S wires. To do this I would use a heavier gauge lead for the
'main' PWM-to-FY20 connection as the current from the connected servos would all flow thru that one wire.

I think the big concern on ground loops is getting high current flowing through a circuit that isn't designed for high current. On the lower current items, a ground loop would be more likely to just induce 'noise' into the system vs burning something out. The noise can be an irritant, the burnt components can be a drain on your bank account when you have to buy replacement equipment.