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Author Topic: Electromagnetic interefrence  (Read 1306 times)

Offline Matt Piatkowski

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Electromagnetic interefrence
« on: July 02, 2020, 06:34:01 AM »
Hello again,
I am looking for credible data regarding the EMI between motor leads.
Each of the leads carries the pulses from ESC and many people say that the distance between the motor and the ESC should be short to minimize EMI and also the resistive losses.

I had to move two Spin44PRO aft to properly balance my eParrot with Himax 3516-1030 contra and the length of leads is now about eight inches.
The elongated motors leads rest in the fuselage on both sides of the 4S 4000 25C battery. They cannot move freely when the battery is inserted and the individual wires are bunched together - three wires in one bunch and three in another.
 
I made several flights with this model and the RPM of both motors were stable, without fluctuations or other "funnies".

Does EMI represent a real threat in the C/L stunt electrical installation and how to assess it?

Thank you,
M



 


Online Crist Rigotti

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Re: Electromagnetic interefrence
« Reply #1 on: July 02, 2020, 06:57:33 AM »
Doesn't look like it, does it.
Crist
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Offline Tim Wescott

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Re: Electromagnetic interefrence
« Reply #2 on: July 02, 2020, 09:19:50 AM »
... many people say that the distance between the motor and the ESC should be short to minimize EMI and also the resistive losses...

What are their qualifications?  If you're going to trust "many people" to make your decisions for you, you may as well just write "yes" on one side of a coin and "no" on the other, and follow its advise.

If you can't credit what people tell you, you'll never get credible information.

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Offline Ken Culbertson

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Re: Electromagnetic interefrence
« Reply #3 on: July 02, 2020, 09:51:18 AM »
Hello again,
I am looking for credible data regarding the EMI between motor leads.
Each of the leads carries the pulses from ESC and many people say that the distance between the motor and the ESC should be short to minimize EMI and also the resistive losses.

I had to move two Spin44PRO aft to properly balance my eParrot with Himax 3516-1030 contra and the length of leads is now about eight inches.
The elongated motors leads rest in the fuselage on both sides of the 4S 4000 25C battery. They cannot move freely when the battery is inserted and the individual wires are bunched together - three wires in one bunch and three in another.
 
I made several flights with this model and the RPM of both motors were stable, without fluctuations or other "funnies".

Does EMI represent a real threat in the C/L stunt electrical installation and how to assess it?

Thank you,
M
I am far from a credible source but I can offer anecdotal observations.  I have been placing my ESC under the wing in what was the space for a pipe tunnel.  That made my motor to ESC  leads around 12"   In my newest design they will be around 15".    By putting the weight of the ESC close to the C/G I was able to go to a 6s battery.  I was concerned about the same thing but it never materialized.   In all fairness, my battery to motor wires were about 3/4" away from the battery at all times.  The spaghetti was in the battery to ESC.  Personally I think the weight of the wires is more of an issue that the length.

Ken
« Last Edit: July 02, 2020, 11:35:17 AM by Ken Culbertson »
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Offline John Rist

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Re: Electromagnetic interefrence
« Reply #4 on: July 02, 2020, 11:19:52 AM »
The issue (as I see it) is that the motor leads do generate some EMI.  However our setup does not have a receiver so that problem doesn't exist.   That leaves the Timer and ESC.   The trick is not to bundle the motor leads in with the lead between the Timer and the ESC.  On KR setup don't bundle the motor leads in with the extra wire that goes to one of the motor leads.  I have read elsewhere that battery lead length is a problem.  Extended battery leads can add inductance that upsets the input filtering.   This is free advice.  It is worth what it cost.    D>K
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Offline Ken Culbertson

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Re: Electromagnetic interefrence
« Reply #5 on: July 02, 2020, 11:44:57 AM »
The issue (as I see it) is that the motor leads do generate some EMI.  However our setup does not have a receiver so that problem doesn't exist.   That leaves the Timer and ESC.   The trick is not to bundle the motor leads in with the lead between the Timer and the ESC.  On KR setup don't bundle the motor leads in with the extra wire that goes to one of the motor leads.  I have read elsewhere that battery lead length is a problem.  Extended battery leads can add inductance that upsets the input filtering.   This is free advice.  It is worth what it cost.    D>K
John, just to be clear, you are talking about the battery to ESC leads, not the ESC to Motor?

Ken
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Offline Tim Wescott

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Re: Electromagnetic interefrence
« Reply #6 on: July 02, 2020, 01:47:51 PM »
So, in my professional life, I've built a brushed motor controller -- basically a 250W ESC with lots of extra features and spread across a 20 square inch board (because we could).  I've worked on systems with built-in brushless controllers (including writing the embedded firmware that made one come alive, which is not a trivial portion of the total engineering), and I've worked on systems that have high-power "noisy" wires running in the same enclosure as low power noise sensitive equipment.

There's a few others in the many people on Stunthanger who are professional circuit designers or work in related fields.

The bottom line: unless the ESC design is screwed up, just keep the motor on the motor side of the ESC, and the batteries and timer on the other side of the ESC, and you'll be fine.  You could only get in trouble if you laid the timer lead up tight against the motor leads, and even then things may still work.  The voltage to the motor is chopped, and that could potentially generate interference, but these things are designed to work with radios; they're certainly not going to mess up a timer without a lot of effort on your part.

But if you'd rather believe the butcher the baker and the candlestick maker on this -- you just go right ahead.

John, just to be clear, you are talking about the battery to ESC leads, not the ESC to Motor?

Ken

ESC to motor is fine; the extra wire length adds inductance, but the motor adds lots of that anyway, so the circuit is designed for it.

Battery to ESC is not fine, unless you put extra capacitors at the ESC.  The analogy that works best if you're not an electrical engineer is a water hammer -- the final drive transistors in the ESC are constantly turning current on and off to the motor.  Inductance in the battery leads, plus the electrical current, acts very much like water in a pipe, that generates a pressure pulse when a valve shuts off rapidly.  In the case of the ESC, what's generated is a voltage spike.  Capacitors absorb that spike (much like a water hammer arrestor), but have to be sized to the length of the motor leads.

(And if there's any circuit designers that want a proper engineering explanation -- go ahead and ask, I'll deliver,  with math & circuit diagrams and everything.  With credit to Igor Burger who pointed this effect out to me pointedly enough that I actually thought it through).
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Offline Ken Culbertson

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Re: Electromagnetic interefrence
« Reply #7 on: July 02, 2020, 03:06:23 PM »

ESC to motor is fine; the extra wire length adds inductance, but the motor adds lots of that anyway, so the circuit is designed for it.

What you are telling me is that my arrangement "may" present a problem.  In the pix, you can see the esc to battery connectors that attach to each other with the xt-60.  Timer is mounted in the cowl above the battery opposite the arming plug and start button.  Motor to ESC 12"  Battery to ECS is 10".  I did not notice any power train issues.  Battery in the pic. is a 5s 3000 30c.   Do I have a problem?   I am designing it's replacement so I can put anything anywhere.  I will be going to the 6s but it is simply wider and there is plenty of that.

Thanks - ken
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Offline John Rist

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Re: Electromagnetic interefrence
« Reply #8 on: July 02, 2020, 03:16:33 PM »
John, just to be clear, you are talking about the battery to ESC leads, not the ESC to Motor?

Ken

I talked about both.  Long motor lead generate emf.  Keep em away from the Timer and ESC and you should be OK.

Long Battery lead can cause inductance that can cause filtering problems.  IE the voltage going into the ESC should be pure DC.  The ESC has input capacitors to filter out spikes keeping it pure DC.   Long battery leads introduces inductance (and resistance) that make it harder filter.
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Offline Tim Wescott

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Re: Electromagnetic interefrence
« Reply #9 on: July 02, 2020, 08:01:26 PM »
What you are telling me is that my arrangement "may" present a problem.

Yes.  Exactly.  The correct answer to nearly every engineering question is "it depends" -- at least until you get into an excruciating amount of detail.

If the ESC is a true brand name with a website behind it, see if you can find an instruction manual -- that should tell you the maximum allowable run from battery to ESC.  I do see caps on the ESC, so it can stand longer wires than when they first came out, with no or minimal caps.
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Offline Ken Culbertson

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Re: Electromagnetic interefrence
« Reply #10 on: July 02, 2020, 11:47:24 PM »
Yes.  Exactly.  The correct answer to nearly every engineering question is "it depends" -- at least until you get into an excruciating amount of detail.

If the ESC is a true brand name with a website behind it, see if you can find an instruction manual -- that should tell you the maximum allowable run from battery to ESC.  I do see caps on the ESC, so it can stand longer wires than when they first came out, with no or minimal caps.
I like to keep things simple.  It is a Castle.  Their Web site is no help.  I have 2 ships that have used this configuration with a simple Huben timer.  I get complete and consistent data downloads so I don't expect I am having any problems.  I still can't get an answer as to how long is "long".

Ken
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Offline John Rist

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Re: Electromagnetic interefrence
« Reply #11 on: July 03, 2020, 09:58:56 AM »
I like to keep things simple.  It is a Castle.  Their Web site is no help.  I have 2 ships that have used this configuration with a simple Huben timer.  I get complete and consistent data downloads so I don't expect I am having any problems.  I still can't get an answer as to how long is "long".

Ken
Simple answer: Too long is when you are having problems.   Not having a problem no sweat ----- GO FLYING!   LL~
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Offline Tim Wescott

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Re: Electromagnetic interefrence
« Reply #12 on: July 03, 2020, 11:24:58 AM »
Simple answer: Too long is when you are having problems.   Not having a problem no sweat ----- GO FLYING!   LL~

That.

(Given the capacitors that have appeared on all the new ESCs lately, I suspect that the ESC manufacturers have gotten tired of telling people not to make their battery leads too long, and have just installed caps.)
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Offline Matt Piatkowski

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Re: Electromagnetic interefrence
« Reply #13 on: July 03, 2020, 11:40:50 AM »
Hi John,
I agree 100% with your simple answer and I am GOING FLYING.
Please see both installations that work in my eParrot.

Even if some EMI exists, I cannot see or hear the detrimental effects of it while doing maneuvers.
Happy Flying,
M

Offline Ken Culbertson

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Re: Electromagnetic interefrence
« Reply #14 on: July 03, 2020, 11:41:41 AM »
That.

(Given the capacitors that have appeared on all the new ESCs lately, I suspect that the ESC manufacturers have gotten tired of telling people not to make their battery leads too long, and have just installed caps.)
Thank you gentlemen, having to redesign my Electronics Bay (EBay?) was going to take the frost off of my mug.

I have just enough slack in my motor leads to twist them a turn or two which would probably help more that shortening them.  Is that a safe statement?   I can also shorten the battery to ESC wires by flipping the direction of the battery and cutting the battery leads a bunch.  That would probably only save weight and I HATE soldering battery leads.  Remember the #1 safety rule when working on electronics - take off your wedding ring?  I was able to get it un-welded but it left a mark.

Ken
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