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HomeAircraftHelicopterHelicopter Main Discussion › Weird Phenomenon
01-08-2015 12:27 AM  3 years agoPost 1
Mitchilito

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Morehead City, NC USA

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I was in the shop this morning and it was still pretty dark in there. I just bought a brand new Trex 550 Dominator with brushless servos and I just happened to manually cycle the tail servo just to see how smooth it was and saw something out of the corner of my eye. So I looked to the front of the heli and did it again and saw what it was. The LED light on JR DSMX satellite (that's hooked up to the Gpro FBL) came on for a second then faded out!!

WTF?!

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01-08-2015 12:33 AM  3 years agoPost 2
Dan Minick

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Columbus, WI

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are you using a BEC? what speed control?

My shop is off limits until it warms up in WI. its 19 degrees in there. no heat on the North end of my house!

Team Synergy, Team FBL Rotors-------if its not broke...it will be!

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01-08-2015 12:43 AM  3 years agoPost 3
Mitchilito

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Morehead City, NC USA

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I've got a CC 20amp Pro hooked up. But there wasn't a battery within 20 feet of the heli!

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01-08-2015 01:12 AM  3 years agoPost 4
jbjones

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Columbus, Mississippi

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I don't have a GED in Physics, but I reckon the only obvious guess is that the servo is acting as a generator of sorts.

Quick, someone hook a multimeter up to an old servo and get to twisting....

I'm very curious if this is true.

-JB

J. B. Jones

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01-08-2015 01:23 AM  3 years agoPost 5
Dan Minick

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Columbus, WI

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oops my bad, i missed the part where you said manually! i was thinking it was powered up

Team Synergy, Team FBL Rotors-------if its not broke...it will be!

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01-08-2015 01:25 AM  3 years agoPost 6
HAV

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Central Florida

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Not weird....turning a servo produces a current... hav

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01-08-2015 02:16 AM  3 years agoPost 7
Retired2011

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Lee's Summit, MO

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Yep...it's called back EMF, I believe!

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01-08-2015 02:18 AM  3 years agoPost 8
Retired2011

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Lee's Summit, MO

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My shop is off limits until it warms up in WI. its 19 degrees in there. no heat on the North end of my house!
Dan...I can't believe your shop is not heated.

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01-08-2015 03:05 AM  3 years agoPost 9
ZS-JAF

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Nazareth, PA

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The UltraGuard on my helis will turn on for a moment when I move servos. An electric motor turns using electric current a generator produces electric current by turning. Some aircraft APU's have a starter motor that also acts as a generator once the APU is running.

I have a 3D heli, I don't understand why it doesn't do 3D.

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01-08-2015 03:36 AM  3 years agoPost 10
EEngineer

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TX

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Yep...it's called back EMF
I always thought back EMF referred to the voltage generated by the collapsing magnetic field of an energized coil...

But that's a weird phenomena....

Was the servo digital or analog?

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01-08-2015 04:09 AM  3 years agoPost 11
Jim Cimino

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NE Pennsylvania

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EMF is any source that causes current to flow. Motors and generators are very similar in design and can sometimes be one unit.

Team Synergy, Team Scorpion, No good deed goes unpunished

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01-08-2015 04:20 AM  3 years agoPost 12
EEngineer

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TX

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EMF is any source that causes current to flow.
Ok...but back EMF is due to a coil's magnetic field collapse in almost all literature....

Also, can't see how it "back-flows" through the servo input voltage regulator/s...

If it's a brushless servo motor, then there's a "mini-ESC" to electronically perform the motor commutation.

If it was a brushed servo motor, I could see that if the motor tapped off from the "red" input lead...and you spun it...then some EMF would be produced...

Anyway, like the OP said, if I was powered down and twisted a servo arm manually....and the DSMX LED blinked....I would be going WTF too.......

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01-08-2015 04:26 AM  3 years agoPost 13
cat5

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Florence, KY

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Something communicating with you from another multiverse universe using the emf you generating. If you keep turning the servo maybe you can pick up a pattern...maybe like morse codes

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01-08-2015 04:31 AM  3 years agoPost 14
EEngineer

rrProfessor

TX

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SETI?......

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01-08-2015 04:40 AM  3 years agoPost 15
icanfly

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ontario

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Not weird....turning a servo produces a current... hav
like those fork mount tire rubbing bicycle light generators, cool.

back emf, no mystery, cool science. If you want a mini generator put a small handle on the servo and take out the stop in it to allow 360deg rotation, one turn would equal probably 1000 of the motor within, if not more.

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01-08-2015 04:42 AM  3 years agoPost 16
EEngineer

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TX

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No measurement equipment needed, right?.....

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01-08-2015 11:42 AM  3 years agoPost 17
Retired2011

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Lee's Summit, MO

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I always thought back EMF referred to the voltage generated by the collapsing magnetic field of an energized coil...
I didn't think the coil had to be energized...but I'm not the EE here.

I think I had back EMF in my intestines last night.

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01-08-2015 11:45 AM  3 years agoPost 18
Retired2011

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Lee's Summit, MO

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The UltraGuard on my helis will turn on for a moment when I move servos.
Mine too...it's sensing current from somewhere.

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01-08-2015 08:43 PM  3 years agoPost 19
Mitchilito

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Morehead City, NC USA

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So of course the brushless motor is acting as a generator but that brings up two questions. How is the three phase alternating current back flowing through the controller to light the DC LED? And since current is flowing is there a potential for damage?

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01-08-2015 08:51 PM  3 years agoPost 20
AWittleWabbit

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O.C., CA

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So long as the lights don't blink "redrum" in morse code and the canopy doesn't spin on the body, you're good!

It's interesting current is going back into power bus.

The servo business needs some good industry standards. I wonder if JR or Futaba servos do that?

Re: solenoids

I did a bunch of solenoid testing recently. You'd be amazed how high the inverse voltage spike can be when you de-energize the coil. The current can tell you when the solenoid actually pulls in too

Heli-itis sufferer.

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