Originally posted by janmb
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Official Freewing MiG-29 Fulcrum Twin 80mm Thread
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Originally posted by Evan D View PostI don't see that there would be differences in potential and the grounds are all tied together so shouldn't be an issue.
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Originally posted by Evan D View PostExplain John, what am I not seeing in what you wrote?
Stray e/m fields create such differences.
There's a lot of e/m around the power leads to the ESCs and motors
Depending on the noise rejection of the receiver, these potentials can be a source of interference.
Presumably Spektrum thinks ground loops can be a problem because (in a slightly different but equivalent context) they specifically recommend NOT connecting the black wire in the pack voltage sensor unless the ESC is opto-isolated (see Andy Kunz's posts in RCG). If the black sensor wire is connected it creates a ground loop. Same thing - receiver ends up connected to ground by two different paths (sensor wire and power wire).
Which is why I recommended doing a range check, preferably with the motor running.
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Originally posted by janmb View Post
You should certainly never input two different battery sources or two different BECs into the same Rx system (without hardware that is intended for it), but the twin outputs on the CC BEC is intended for exactly that.
"The use of redundant parallel fight packs (packs may be of different capacity but MUST be of an equal number of cells) is an excellent way to increase the available flight time and significantly improve the reliability of the on power system. The simplest means is to run two complete wiring harness, switches and charge jacks from each pack and plug one into the normal battery port and the other into an extra channel on the receiver. No diodes or isolation is required (see below). This is simpler and more reliable than some of the complex battery backup systems being offered on the market."
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Originally posted by janmb View Post
The twin outputs on the CC BEC has common ground. So no.
The receiver is connected directly to the BEC ground when plugged into the BEC. It is also connected by servo leads to the bluebox (MCBe) which in turn is connected to the other CC BEC ground when connected as described. Hence there are two separate connections between the receiver and the circuit ground. This, by definition, is a ground loop.
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Originally posted by Evan D View PostPlus the receiver is connected to the MCBe. I see no issue. No possible ground loop or differences of potential.
The original post that started this discussion:
Originally posted by Legman01 View Post
Thanks for the info Rich, I have a similar setup but haven't flown the maiden yet. What is your reasoning for plugging the second BEC lead into the Blue Box, instead of into another receiver port as per the manual with the Castle Pro?
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Originally posted by Evan D View PostThat there is a ground loop is not a issue. That there is a difference of potential is the possible issue and for this situation there isn't.
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Originally posted by kallend View Post
The loop would be created when plugging servo leads from the Rx into the blue box (MCBe). The common ground in the BEC doesn't prevent that.Freewing A-10 turbine conversion: http://fb.me/FreewingA10TurbineConversion
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