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Author Topic: Power versus control signal  (Read 2030 times)
Jim Fruit
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« on: July 22, 2011, 10:43:39 AM »

Clancy:

I am flying right along in the construction of my next scale subject (the Beech D-18). It is, of course, a plane of a rather wide body with twin engines out on the wings. I am going to take advantage of the wide body to contain your decoder and two 11.1 volt batteries (one for each of the electric motors). Then each of the engine nacelles will contain an ESC for each motor, the motor itself and retracts. All of this is just to give you an idea of the configuration.

Now to the foolish Electronics 101 question. I used to work for a design engineering firm and one of my tasks was to review the constructability aspects of our designs. I was always careful to make sure that our designers did not create too close of a proximity between our higher voltage (120 V+)wires and those that carried our 4/20mA control signals. Should I concern myself about the proximity of the 11.1 volt motor power wires and your 0 to 5 ohm signal wires? I could wrap the the signal wires in a foil or something if it were needed. I feel a little foolish asking this question when I realize that the power and signal wires are already in close proximity around the motor anyway. However, I read an article in the current American Modeler in which the author said he coiled the red and black power wires to reduce interference! I had never heard about that method, but the comment makes me wonder about the application.Do I need to concern myself?

Lastly, if I have a separate pot, use separate channels, battery and ESC for each motor, do I still need to cut the signal wire on one of the assemblies or are they completely independent? Thanks for your help.

Jim Fruit
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Tim Wescott
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« Reply #1 on: July 22, 2011, 10:53:47 AM »

I'm not Clancy, so if he contradicts anything I say believe him and not me.

But:

Don't do anything really stupid like running one signal wire next to one motor wire, and the other signal wire next to the other motor wire, with everything all seperate.  As long as like is twisted with like (motor with motor, battery with battery, teeny with teeny), and they're not all twisted up together, then you're probably going to be fine.  I would try to maintain some separation, and I would try to keep wires running at right angles -- but if you've got a couple of inches where the wires all lay together you're probably fine, particularly if they're twisted.

I'm assuming that Clancy's system works the same as RC, in that it needs an on-board battery for power.  If that's the case then you want to cut the power wire coming from one of the ESCs, but you want signal going out to both of them. You don't want to cut the signal wire on either of the assemblies under any circumstances -- that'll just make that ESC/motor/battery combo into a giant, expensive paperweight.
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Jim Fruit
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« Reply #2 on: July 22, 2011, 12:18:39 PM »

Thanks Tim. I am a newbie to the total electrics, that is why the silly questions.

I have not heard of the "twisting" of a run of wires. Do we know why that would reduce the effect of high voltage on very low voltage? I won't really have any right angle relations of wiring that I can envision. Batteries in the body; ESC and motors in the nacelles. Therefore the power wires run parallel to the wingspan. Clancy's decoder (similar to the receiver in R/C) will be in the body also with control wires running out to the nacelles parallel to the power wires. I probably can separate those two runs by as much as 6 inches.

Clancy's system can run with a BEC or a separate battery to power it and any servos. I think I am going to use a separate battery source instead of the BEC. Would that eliminate the need to cut the power wire?

JHF
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Tim Wescott
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« Reply #3 on: July 22, 2011, 12:50:45 PM »

First, I want to say that I am probably going way, way overboard here.  My instincts for wiring harnesses were developed working on systems that carried video over shielded twisted pairs, in 100 feet of cable that was also carrying raw vehicle power in wires laying right next to the video.  Video is way way more noise sensitive than the digital signals that tell the ESC what to do, and your motors draw way way less current than the stuff that was making that video.

So you can probably wire your plane any old which way, and it'll probably work just fine.

Thanks Tim. I am a newbie to the total electrics, that is why the silly questions.

I have not heard of the "twisting" of a run of wires. Do we know why that would reduce the effect of high voltage on very low voltage?

First, your voltage differences here aren't all that significant.  What is significant is the current in the wires.  Current induces magnetic fields around the wires that carry the current (like the battery wires).  Varying current induces varying magnetic fields.  Those varying fields will, in turn, induce voltage on nearby wires -- like your signal wires.  The more current that's induced, the more voltage will be induced (hence the concern).  The less overall coupling there is between the sets of wires, the less voltage will be induced.

If you arrange sets of wires so that all the wires in the set are laying close together then they'll tend to cancel out their own magnetic fields, and they'll tend to be less sensitive to impinging magnetic fields.  So you want you want the wires dressed so that related wires (like the + and - battery wire) are tight together.  Twisting the wires a bit helps to keep them laying together.

Twisting the wires also helps because if you have the + battery lead laying against the signal lead, then a little while later the - battery lead doing the same thing, then the effects of the current in that battery lead will tend to cancel out.  So if you twist the two sets of wires with a different pitch then you'll reduce the coupling still further.  This is easy enough with battery wires and signal wires -- just twist them naturally, enough so they hold together, and because they're such different sizes they'll naturally tend to have different twist pitches.

So twist reduces coupling because it reduces the distance between the wires, and because it breaks up the tendency for wires to "talk" to each other.

Quote
I won't really have any right angle relations of wiring that I can envision. Batteries in the body; ESC and motors in the nacelles. Therefore the power wires run parallel to the wingspan. Clancy's decoder (similar to the receiver in R/C) will be in the body also with control wires running out to the nacelles parallel to the power wires. I probably can separate those two runs by as much as 6 inches.

Use right angle relations if you can.  If you were to run the battery wires and the signal wires (both ground and signal to the ESC) randomly in a tray, then you may 'un-luck' out and cause ESC problems.  Chances are low that this will happen.  You've got a bigger chance that a loose connection in a battery ground wire will mess you up.

Twist the wires enough so that they're neat and tidy, run the signal wires an inch or more away from the battery leads if it's convenient (and run them right together if its not), and make sure you have good battery connections, and you should be fine.

Are you running one battery per motor, or one battery for the whole plane?  How many cells?

Quote
Clancy's system can run with a BEC or a separate battery to power it and any servos. I think I am going to use a separate battery source instead of the BEC. Would that eliminate the need to cut the power wire?

No!

The BEC is going to try to power your receiver if you connect it up.  With two BECs and a battery in there, you'd have three different power sources and just one power sink, all connected to the same piece of metal.  Chances are high that what would actually happen would be that the BECs would just float and not deliver any current -- but one or the other of them may also try to charge your battery for you, in a totally uncontrolled fashion.  Unless Clancy's system leaves the power leads unconnected for you, clip those leads!
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Jim Fruit
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« Reply #4 on: July 22, 2011, 02:27:03 PM »

Thank you so much, Tim.

All great and helpful information. I signed on to this website a couple of month's ago per Clancy's recommendation. I have since found that it is an unbelievable source for expert advice, such as yours, on virtually any item. I also am surprised at how far reaching the coverage is. Such is the scope of the internet, I guess. What is your "20"?

I am planning to use one battery per motor assembly (two total). I can utilize just one, but believe it or not, two of my 3-cell, 2100 mah batteries are about 3 ounces less than one of my 3-cell, 4300 mah batteries. I am building the model to a rather small scale (1" to the foot), so I believe I am going to attempt to hold the weight down. Along that line, From your comments, I also believe I will now power Clancy's decoder from one of the BEC's rather than a separate power source. That might save another 3-4 ounces.

Thanks again for your help.

JHF
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Tim Wescott
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« Reply #5 on: July 22, 2011, 03:28:15 PM »

I'm in Oregon City, Oregon (actually I'm about eight miles east).  If you click on someone's name in a post you'll bring up their profile, and if they put their location in there then you can see it.
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Clancy Arnold
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« Reply #6 on: July 22, 2011, 04:44:10 PM »

Jim
Tim is correct in all of his recommendations.  The big advantage of twisting the pairs of wires is that the coupling in one part of the wire is canceled out in the next twist.

The problem that causes this type or interference is high impedance circuits.  The design of the U/Tronics Control units reduced or eliminated high impedance circuits where ever possible.  The output impedance of the Encoder is 150 ohms.  That eliminates the noise problem in question.

Jim
The coiling of the battery wires is not bad but not needed unless he has a problem of another nature.

Hooking up the Decoder to operate two ESC's:
The output cables from the Decoder to each ESC needs a ground (Black) wire connected and a Color Signal wire connected.  If you are using a separate battery pack to power the Decoder then neither Red wire should be connected to either ESC.

If you wish to power the Decoder from the BEC circuit in one of the the ESC's then DO connect the Red wire to that ESC and tape over the battery power input connector on the Decoder.  In either case you are providing power to the Decoder from only one source.  I have added the information about connecting the U/Tronics Control unit output to two ESC's in the special use thread.

As for the weight of the separate battery pack, I am sending you a set of 4 AAA  NiMH Batteries to try.  They weigh 1.3 ounces but have 1000 mAH capacity.  That is almost twice the power of a set of AA NiCad's which would weigh over 4 ounces.
Clancy
« Last Edit: July 22, 2011, 05:08:20 PM by Clancy Arnold » Logged

Clancy Arnold
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U/Tronics Control
U/Control with electronics added.
Clancy Arnold
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« Reply #7 on: July 22, 2011, 05:14:16 PM »

Jim
You mentioned using two controls for the separate throttles.  I did that on my P-38 and to make a long story short, I pushed up the right throttle only and ground looped the model.  I then added a switch to "lock together" the throttles.  I will enclose a drawing with the batteries.
Clancy
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Clancy Arnold
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Jim Fruit
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« Reply #8 on: July 22, 2011, 07:11:20 PM »





Hooking up the Decoder to operate two ESC's:
The output cables from the Decoder to each ESC needs a ground (Black) wire connected and a Color Signal wire connected.  If you are using a separate battery pack to power the Decoder then neither Red wire should be connected to either ESC.

If you wish to power the Decoder from the BEC circuit in one of the the ESC's then DO connect the Red wire to that ESC and tape over the battery power input connector on the Decoder.  In either case you are providing power to the Decoder from only one source. 
[/quote]

Clancy

In your opinion, which way do you think I should go? A separate battery source or a BEC. Which would be a cleaner/more fool proof installation?



As for the weight of the separate battery pack, I am sending you a set of 4 AAA  NiMH Batteries to try.  They weigh 1.3 ounces but have 1000 mAH capacity.  That is almost twice the power of a set of AA NiCad's which would weigh over 4 ounces.
Clancy
[/quote]

Thanks, Clancy, it was not necessary for you to send me anything. I appreciate it.

Jim
You mentioned using two controls for the separate throttles.  I did that on my P-38 and to make a long story short, I pushed up the right throttle only and ground looped the model.  I then added a switch to "lock together" the throttles. 
Clancy

I remember you commenting about your experience with separate throttles. I just knew you would react upon hearing my plans to do so also. I appreciate your concerns, but I envision several scale operations that it may introduce. I need to learn to fly it like the real thing.

Thanks again.

JHF
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Clancy Arnold
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« Reply #9 on: July 23, 2011, 08:36:49 AM »

Jim
I would recommend that you power the U/Tronics Control Decoder from the BEC circuits in one of the ESC's.  Least items to work with.  One set of batteries less to charge.  If you follow the instructions at the bottom of the Dual ESC drawing you should do fine.

The thing I would recommend is adding the Throttle lock switch so that "while flying" you have the throttles working together.

I will add a drawing to the special use thread to show how to wire up the Throttle lock switch.
Clancy
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Tim Wescott
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« Reply #10 on: July 23, 2011, 11:33:13 AM »

With slide pots you can put two throttle levers right next to each other, like the throttle quadrant on a scale airplane.  This should make it natural easy to push both up together.

Pushing up just one throttle instead of both is probably a mistake that the full scale guys make, too -- but I think if you started developing the habit from day 1 of pushing both up together that you could get by.  And being able to do 'one engine out' flying would make for a nice scale maneuver.  Now you just need braking ESCs and a pair of props that'll feather...
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Jim Fruit
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« Reply #11 on: July 23, 2011, 04:44:44 PM »

Tim:

That is sort of how I intended to set them up (next to each other). I wasn't thinking so much about an "engine out" as I will have plenty of other options available. I was thinking more in terms of a "start one" and "start two" to further verify the throttle control to the judges. I understand Clancy's concern, but I guess I am sort of stubborn.

Thanks for the clue about clicking on the author's name in a post. I am still learning. What I can't seem to master yet is the inclusion of a previous quote. Sometimes it works, most times it doesn't

JHF
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Tim Wescott
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« Reply #12 on: July 23, 2011, 05:26:56 PM »

That is sort of how I intended to set them up (next to each other). I wasn't thinking so much about an "engine out" as I will have plenty of other options available. I was thinking more in terms of a "start one" and "start two" to further verify the throttle control to the judges. I understand Clancy's concern, but I guess I am sort of stubborn.

I want an ESC that'll spin the motor really slowly for two revs, then start going faster -- like the real radials start.  Of course, without the puff of black smoke and the noise it'll still be missing something.

Quote
Thanks for the clue about clicking on the author's name in a post. I am still learning. What I can't seem to master yet is the inclusion of a previous quote. Sometimes it works, most times it doesn't

open square bracket, the word quote, end square bracket.

This may work, if using the 'code' feature turns off parsing the special markups:

Code:
[quote]Your quote here[/quote]

Hey! It worked!

To get a quote like

Quote from: Jim Walker Hisself
Now go build something!

I did

Code:
[quote author=Jim Walker Hisself]
Now go build something!
[/quote]
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