Official Freewing MiG-29 Fulcrum Twin 80mm Thread

[kallend]

The twin outputs on the CC BEC has common ground. So no.

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.

[Evan D]

I don't see that there would be differences in potential and the grounds are all tied together so shouldn't be an issue.

[kallend]

I don't see that there would be differences in potential and the grounds are all tied together so shouldn't be an issue.

The whole issue with a LOOP is that stray e/m fields create such differences. That is why loops are bad. And there's a lot of e/m around the power leads to the ESCs and motors.

[Evan D]

EMI from power leads to the ESCs and motors is not a ground loop and a totally different issue.

[kallend]

EMI from power leads to the ESCs and motors is not a ground loop and a totally different issue.

I didn't write that it is. Re-read what I wrote.

[wolpertinger]

Looking to add brakes on my Mig 29. Saw these at RC Castle. Has anybody used them?

[Evan D]

Explain 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

[Skosh25]

Finished my first ever repaint today. Happy with how it turned out. Quite the learning experience. Now time to get her back in the air!

[kallend]

Explain 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

The ground loop is the continuous conductive path (BEC - receiver - bluebox - BEC) of the circuit ground when the BEC is connected both to the receiver directly and also via the bluebox. That acts like a loop antenna, and any e/m that intersects the loop will generate currents in the loop that in turn lead to potential differences around the loop.

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.

[RC Rich]

Finished my first ever repaint today. Happy with how it turned out. Quite the learning experience. Now time to get her back in the air!

Great paint job! I like the scheme and it will show up nicely in the sky.

[Griffon Wings]

Finished my first ever repaint today. Happy with how it turned out. Quite the learning experience. Now time to get her back in the air!

Great job Sir, i saw few pilots doing this color on the mig, gonna look great in the air. BRAVO !!

[radfordc]

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.

Using two Rx batteries plugged directly into one Rx is quite common and is considered good practice.

http://www.hangtimes.com/parallel_packs.html

"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."

[kallend]

The twin outputs on the CC BEC has common ground. So no.

That isn't the point.

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.

[Evan D]

Plus the receiver is connected to the MCBe. I see no issue. No possible ground loop or differences of potential.

[kallend]

Plus the receiver is connected to the MCBe. I see no issue. No possible ground loop or differences of potential.

Is the MCBe also connected to the CC BEC, like the receiver is? If it is, that right there is your ground loop.

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?

[Evan D]

That 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.

[kallend]

That 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.

You are missing the entire point. Whenever there is a ground loop (which there is if connected that way) then any (ANY) e/m will lead to currents in the loop and therefore potentials. That includes e/m from the ESC and power leads. Faraday's laws. Basic physics. Basic circuit design.

[Evan D]

Nope, sorry. I understand your point and with the way he's connecting there will not be differences in potential, at least significant to be noticeable. No issue.

[janmb]

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.

It is the intention of this config in the first place. A loop is NOT bad in this case.

[Airguardian]

So, here's some progress on the MiG-29.
The GF laminates to reinforce the stab assemblies are done.
Almost ready for maiden now :)