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Old 01-04-2014, 06:52 PM   #1
DavidR8
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Default Ferromagnetic choke

Last week I pulled the wing off my Fun Cub for the first time. I both this plane fully built and know it flies well because a local club flier told me the maiden flight (and it's only flight) was perfect.

One thing I noticed is that the servo connections are run through and around a circular magnet about 3/4" in diameter.

I recall this is done to reduce electrical RF 'noise' (I think) but have never seen it mentioned in any build forum.

I'll post some pics later today but I'm curious about initial thoughts.

Flying more, crashing less. Feels great!

Champ, Super Cub, Fun Cub
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Old 01-04-2014, 07:06 PM   #2
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The only place you usually see those ferrite chokes are on the wire that runs between the ESC and the receiver. That's to stop the noise from the switching circuit in the ESC being transmitted into the receiver. Not really an issue with 2.4GHz but does no harm to have it there.

I've never seen them on servo wires. No doubt they are there to choke out electromagnetic and RF interference, but I've never experienced any problems when running without them.
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Old 01-04-2014, 07:17 PM   #3
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Ya that's a weird one like it has been mentioned I have only seen it on the ESC.

Dave your gonna love this plane I take it to the field most every time I go.
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Old 01-04-2014, 07:23 PM   #4
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Never hurts to put the choke in.

But usually there's not a good reason to put it in. Extremely long servo extensions could benefit from it.

There's also a "glitch trap" that could be added in a long wire. Made with an inverter gate (forgot the chip number) double-inverting the signal and boosting it to full RX buss voltage.

These "tricks" were more common with 72 mhz (USA... I think its 35 or 40 mhz in UK?) which was more sensitive to the interference that could come from ESCs and long servo leads.
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Old 01-05-2014, 01:24 AM   #5
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The giant scale guys used to use those chokes on long servo leads a lot back in "the day". Long servo leads could pick up interference and feed it back into the rx.

Modern gear is far more robust and those chokes are rarely needed with our new rx's - and then mostly only on the esc channel. I havent seen an install that needed one in a long time though.

I think I need a signature.
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Old 01-05-2014, 02:34 AM   #6
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Originally Posted by DavidR8 View Post
Last week I pulled the wing off my Fun Cub for the first time. I both this plane fully built and know it flies well because a local club flier told me the maiden flight (and it's only flight) was perfect.

One thing I noticed is that the servo connections are run through and around a circular magnet about 3/4" in diameter.

I recall this is done to reduce electrical RF 'noise' (I think) but have never seen it mentioned in any build forum.

I'll post some pics later today but I'm curious about initial thoughts.
Yeah
Those were used to reduce electrical noise from the ESC from getting into the 72 Mhz receivers. Especially if you're running brush type motors on more than 20 Nih cells.

Back in the late 1990's, I had an Astroflight Geared 90 brush type motor that was running on 38 sub C Nicad cells. Radio interference was so bad, I only had about 10 feet of radio range. With the transmitter antenna fully extended.

Finally reduced the radio interference to tolerable levels by running the motor leads through a pair of those ferrite chokes, one for each motor lead.

Nowdays, it is not easy to generate 2.4 Ghz (That's 2400 Megahertz) unless you've got specialized chips to do the job. You're not going to generate 2.4 Ghz interference from things like motors, or ESC's.

I did see one of those ferrite chokes on the leads of a Common Sense uBEC awhile back. Mostly to eliminate the 72 Mhz radio noise from the uBEC's switching regulator. The Castle Creations uBEC's don't use them. But for me, on 72 Mhz, I'd install one of those ferrite chokes on any 72 Mhz receivers with the CC uBECs. Just in case. (I've measured a fair amount of radio noise on the CC uBEC's battery power leads.)

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Old 01-05-2014, 08:51 AM   #7
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Default I'm running 2.4 Ghz gear

So I think it will be ok.

I knew if I asked the question here I'd get a wealth of excellent feedback!

Flying more, crashing less. Feels great!

Champ, Super Cub, Fun Cub
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