Replies to This Discussion

Permalink Reply by Peter Chaffe on July 1, 2012 at 3:12pm

The term 'Ground loop' can cause confusion in this application, There is no ground as such on these circuits, just negative return path's. These paths, being wire or pcb track, act like resistances!

Multiple return paths will carry different amounts of current depending on load, so multiple negative paths will have small voltage differences depending where measured, and on what path, the amount depending on current flow, these would normally go unnoticed on pure dc applications but spikey current demands like in alternating power output stages, audio, video systems, Computer and especially automation as in cnc machines, and in our case ESC's are the worse cases. Problems can range from occasional glitching to complete havoc.

Wiki NinjaPermalink Reply by Gary McCray on July 1, 2012 at 3:02pm

Yes there is a small ground loop potential created by individual ESCs drawing power, but it also spreads the current loading and since it is common bussed at the APM board it would actually serve to reduce ground excursions, spread current load and increase (very slightly) battery efficiency.

Still, you are right, it is generally a good idea to avoid ground loops and in this case, in the event of a catastrophic ESC failure, it might be able to damage the APM board.

Following your concept, even if you were using the power from one or more of the ESC built in BEC's or even a standalone you would still only want to use the + 5 volt power wire(s) and not connect any of the BEC output grounds to the APM.

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Permalink Reply by Bruce Jones on July 1, 2012 at 3:10pm

And this is where these discussions always go - into ambiguity.  Maybe there aren't hard fast rules on the best way to wire these things, but I certainly wish there were.

Regardless of whether spreading the current load (and battery efficiency and failure syndication) across multiple ESCs is a better or worse idea than potential ground loops, it sounds like nobody argues that powering the APM with a separate BEC is a bad idea?

And if you do that, only the signal line should come from the ESCs?  And power to the Tx through only a single line?  And maybe the current sensor should only send signal too?

How would you measure ground loop - different voltage measurements across power and different ground points?

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Permalink Reply by Norman Sanchez on July 2, 2012 at 2:50pm

Three years without any type of electrical problems, a bec for apm and one for camera and other, protege with silicone sonar, gps protected with heat shrink and compass, no problem orientation and magnetic fields.

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Permalink Reply by Gustav Kuhn on July 2, 2012 at 8:04am

Not quite,

Best practice is to connect all the ground wires, ESC, battery, and the Signal grounds, to a common point.

And by that I mean something like the supplied Power Distribution Board.

And if you search a bit to previous posts, you'll see what I did to be able to run the APM from ALL the BEC's, using Shottky diodes.

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DeveloperPermalink Reply by R_Lefebvre on July 1, 2012 at 3:37am

Really Marco?  It causes flight problems if you power by BEC?

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DeveloperPermalink Reply by Marco Robustini on July 1, 2012 at 3:47am

Yeah Robert, i think this is the cause of my latest crash during test...
It was the first time I powered my APM2 with esc, never again! :-)
Others my drone have one or more dedicated bec.
Having a "clean power" is important.

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Wiki NinjaPermalink Reply by Gary McCray on July 1, 2012 at 3:13pm

I and a friend are each powering our KK X525's APM2 board with the provided ESC's BECs which are all connected power and ground to the ESC out connector on the APM2.

These use linear voltage regulators that seem to work well in parallel and when one of the motors is drawing enough power to pull it's BEC down a bit one of the others can in theory compensate.

They will not provide more than the rated power of a single BEC but can compensate (a bit) for local sag.

This is a controversial approach, but at least in this instance it has worked well, with many hours on each Quad.

A high quality single dedicated BEC is likely a safer alternative.

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Permalink Reply by Tye on July 1, 2012 at 6:19pm

  

     There are several good reasons not to use the BEC that's part of an ESC...not to mention the fact that it is competing for the same electron flow as the motors.... I also fly 3d type helis and you won't find too many folks flying with ESC BECs most use a stand alone bec hooked to it's own small lipo or they'll use a big nicad flight pack with out a bec all togeter....

 

 

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Permalink Reply by Bruce Jones on July 1, 2012 at 12:10pm

I do indeed power my APM2 through and ESC's BEC, not a separate one.

Initially I tried powering it with a dedicated BEC, but I must have done something wrong because I couldn't get enough power (1.3 volts) out of the Receiver pins to power my receiver.  So I gave up and just used the ESC.

Maybe I should look into it again.

I really hope that APM3 has better power management, it seems to be very weak in this area.

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Wiki NinjaPermalink Reply by Gary McCray on July 1, 2012 at 3:27pm

Assuming the stand alone BEC can deliver sufficient current (2 + watts) and that its power lead is attached to one of the APM ESC connectors center (power) pins it normally should be able to work just fine for an APM2 and most receivers.

An APM1 will need a higher current BEC.

The only possibility I can think of where this might not work is that if it is a switching BEC, it is possible that it might have a ground that is not referenced to it's power input ground and is in fact floating.

If that is the case, the BEC's output ground also has to either be connected to the central ground at the power distribution board or one of the outside pins on the APM board.

I do not think that this is likely and I would avoid a BEC with a floating ground in any case.

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Permalink Reply by ward on July 1, 2012 at 4:02pm

Could we join (OR) the positive lines of the BEC's together through Schottkey diodes?  On diode on each 5volt line.  This would give redundancy and my help reduce the ground loop. 

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