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Old Jan 06, 2014, 10:09 PM
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Australia, SA, Adelaide
Joined Jul 2013
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Question
Where to connect positive motor wire on old micro rtf rc receiver

I am building a scratch built new plane from and old receiver module from this flying insect.


The motor wire came off and I can't remember where it should go, you can see the negative motor wire at the top right, does anyone know where the positive would go?

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Old Jan 06, 2014, 11:37 PM
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Joined Nov 2008
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Not an absolute answer, but as a general principle N-channel MOSFETs work so much better than P-channel that a unidirectional brushed-motor PWM speed control is almost always built with the FET in the negative line. The positive motor lead then goes directly to the battery input.

Of course just because that's the sensible way to design it doesn't absolutely mean the one you are working on works that way.
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Old Jan 07, 2014, 12:30 AM
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Ok thanks, I was considering connecting both motor wires directly to the battery for an always on motor (with nimh's), but it probably wouldn't be good if the battery voltage drops and the rx goes off but the motor stays on, lol.
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Old Jan 07, 2014, 01:24 AM
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Unfortunately I broke it some how trying to solder these micro joins etc.

Oh well I don't think the range was great anyway.


Might have to make a free flight model instead.
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Old Jan 07, 2014, 10:42 PM
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Most of the time, wire fatigue from frequent flexing will cause the wire to break. This will be just below the end of the insulation, near the solder joint.

You can find out where the wire broke by getting the highest optical magnification you can - preferably 4X or so. You can get an inexpensive jewelers loupe for about 10 bucks. Carefully scan the board and you will find tiny frayed wire strands sticking out, barely, just beyond the solder joint. That's where it goes.

Incidentally, I used this process earlier today to find where a wire broke off of one of my prized YGE-4S ESC's!!
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Last edited by 356Jim; Jan 07, 2014 at 10:58 PM.
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Old Jan 07, 2014, 10:57 PM
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West of California Speedway, East of LaLa, North of Disneyland
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I think I might have found where the wire goes, but first, a question. What's the deal with the black wire hanging loose on the right side of the pic?

If you look toward the top of the pic you posted, and right above the board marking for "C21", there is a solder joint with a few minute strands of wire sticking out toward the right.

To be sure, if you have a voltmeter, then power up the board and see if that solder joint reads the same as the batt voltage. Then check if the red wire length to that pad seems reasonable. See if the broken strands match. If so, that might well be the place.

Now, a disclaimer. I was wrong in 1983, when I predicted that Rick Mears would win the Indy 500. Sadly, I was wrong. He came in third.

Another disclaimer. I joke a lot!! Other than that, I'm serious.
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Old Jan 08, 2014, 03:17 AM
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Thanks for all the help, but I ruined it with the soldering iron already.

I soldered and unsoldered lots of times, I think I'm going to build future micro's with the new micro rx's and low voltage small servos that I can use with the new Frsky Taranis I ordered that should be arriving anyday
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