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Old 06-01-2008, 05:51 AM   #1
kyleservicetech
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Default "Dry Testing" brushless motors (Update Sept 10 2008)

Some of us may have run across a brushless motor that has questionable operation, perhaps after overheating it, or after crash damage. It may even have come from a swap shop. The question is "Do you want to connect it to an ESC" and risk possible damage to the ESC? (I'm a retired Service Tech with 45 years experience in troubleshooting, and repairing electronic controls for high power 38,000 volt circuit breakers.)

Electrically, these motors are not really complex, and can quickly be checked out for problems. All that is required is a variable speed battery operated drill, and a AC volt meter or digital multimeter. These brushless motors are three phase motors, or perhaps a synchronous three phase motor with a variable speed electronic drive, the ESC units we are familiar with. In fact, with a four channel Oscilloscope, and three resistors (star) wired in to provide a neutral connection for the scope, you can look at a three phase voltage waveshape signal from any of these brushless motors.

For what it's worth, this is how I've checked out various motors and automotive alternators that I've wound up or rewound. (Ten years ago, I rewound an automotive alternator to put out 70 Volts at 5 Amps. It was used along with a 3.5 Hp Briggs and Stratton engine as my design peak charger for the 38 Nicad Cells used in a 1/4 scale Piper Cub model airplane. This model was powered by an Astroflight 90 geared motor with a home made gearbox.)

First:
Disconnect the motor (ISOLATE ALL THREE WIRES FROM EACH OTHER!) from the ESC, chuck it into the drill, and slowly wind it up while holding the stationary part with the three lead wires. The rotation should be very smooth, with no rattling, virtually no noise. Also, their should be very little drag. Run the motor with the drill at full speed (1000 RPM or higher if possible) for a minute or two. Nothing inside the motor should get warm or hot.

If so, you've got a shorted winding or two, you've got a real problem. Or, a magnet has come loose, dragging against the stator inside the motor. Also note if the "bell" of the motor wobbles while running the motor. If so, it can result in the magnets hitting the stator. (The Hacker 40, 50 and 60 series outrunner motors have a third ball bearing to prevent this from occurring)

Second:
Keep the three motor wires isolated from each other, and label them #1, #2 and #3. Connect your voltmeter to an AC range, and connect to terminals #1 and #2. Wind up your drill to full speed, and write down the AC voltage. Then repeat this test on terminals #2 and #3. And again on terminals #3 and #1. All three voltage readings should be near identical, providing your drill is running at the same speed on all tests.


Third:
Short circuit all three wires together directly at the ends of the motor windings. Then SLOWLY wind up the variable speed drill while holding the stationary part. Be careful, you will have considerable drag where the motor will try to twist out of your hands. This drag will be very even, with little variation, and no "Chugging". As a comparison, only short two wires, and try again. This test will be very obviously much less smooth than when all three wires are shorted. Don't run the motor more than 5 or 10 seconds, as the windings will get warm doing this. (Don't use jumper wires, we are generating 20-30 Amperes or more of current at very low voltage, jumper wires won't work.)

Four: 06/03/08
Ron van Sommeren suggests checking for short circuits between the windings and the stator. Good idea. Since the windings are all connected to each other, check for any connection between the motor stator laminations and the windings. Look for bare metal somewhere on the stator for one connection to the meter, and the meter windings to the other. If no steel bare spots are available, you will need a needle point on one of the meter probes to punch through the coating of the steel laminations. The meter should show an open circuit, or infinite reading. Again, any connection is bad news, and is cause to scrap the motor. (Or if you've wound the motor your self, unwind, and do it again, but more carefully.)

Five: 06/05/08
Coro reports that it is a good idea after the motor passes the above tests, to check the motors "no load current", and compare it with the manufacturers specifications. This also will potentially identify "shorted turns" in the motor. FYI, a shorted turn is a single winding, (or more than one single winding) that "has shorted out". What this does, is that shorted turn becomes a very high current generator when the motor is running at full speed. Since the winding is shorted, the motor develops short circuit current through that shorted turn winding. This results in very high temperatures of the shorted turn, and will lead to serious motor failure. This would place your ESC at risk.

Only way to repair a shorted turn, is to replace, or rewind the motor. One possible cause of "shorted turns" is running the motor beyond its maximum current rating, overheating the motor to the point where the varnish insulation on the motor windings is damaged.

I've worked with "Double Formvar" magnet wire before I retired. This stuff is rather impressive. It will pass a high voltage hipot test directly on the surface of the varnish and the wire directly underneath of 12,000 VOLTS. This double formvar wire is what I used to wind my go-brushless motors.

6/5/08
Brian Click Wrote:
Another tip (I'd add it to the WF forum but haven't signed up there yet) is to use a DMM and terminating resistor (or small lamp) connected across a winding phase to measure the generated current...

Spin up the motor using a cordless drill and measure the voltage (AC of course), and note the reading. Then do the same for the other two phase connections, and compare readings.

All 3 measurements should be the same and if they're not - you have a shorted turn or missing / extra turn. Or your drill battery is dying between runs

You should also touch one wire to the motor's frame (to check for shorts to the pole piece) while doing each phase test; there should be NO change in the reading.

If you have an oscilloscope, you can use that as well, to look for distortion and/or amplitude variations in the waveform. Distortion indicates a shorted winding.

(Kyleservicetech: Note, the wave form I've observed is not a really pure sine wave. Depending on the motor brand and so on, you are likely to see the top of the sinewave a little flat, along with other minor changes. BUT, all three phases should show identical waveshapes! If you have access to a four channel scope, get three resistors, about 270 to 1000 ohms each, connect all three together on one end. Take the other ends of the three resistors and connect it to the three motor wires. The common (wye) center of the resistors is your connection to the scope ground, connect the three channels to "phase A, phase B, phase "C" respectively. Then spin the motor! You will see a three phase voltage signal.)

Amplitude variations indicate turn imbalances between poles and can even reveal weak magnets in the rotor and/or spacing (magnet to stator clearance) variations or a (badly) out of round rotor, assuming turns are known to be correct.

Dennis / (Kyleservicetech)
I've got one Hacker A30, one Hacker A40, and two Hacker A50 motors plus a half dozen hand wound go-brushless motors. The Go Brushless motors were checked per above before connecting to an expensive ESC. Found a few problems such as shorted turns with this procedure that saved the ESC.



And, lastly, before connecting the questionable motor to your ESC, you may want to put a temporary fast blow type instrument fuse in series with the battery and the ESC. Typical fuse size would be on the order of 10-15 Amps for an ESC of 40 Amp rating or higher, and 5-10 Amps for the back yard flier type.


Be certain to slowly wind up the motor without a prop with the small in line temporary fuse during testing, since quickly winding up the motor can blow the fuse due to high starting currents.

06/05/08
Other responses in this thread indicate that current limited power supplys should be used carefully. Don't know if this is an issue or not. I suspect that anyone that has access to a current limited power supply like this would also have access to a good oscilloscope which can be used to monitor the DC voltage output of the power supply. The scope would be used to watch for any wild DC output voltage fluctuations while running the ESC and brushless motor.

For testing, I use my home made variable DC power supply that has a rating of 25 VDC at 25 Amps. Output capacitor on this supply is 0.2 FARADS! The capacitor is a special industrial type with very low internal impedance. (The power transformer and reactor on this supply also were hand wound!)

Note that only outrunner motors should be run with no prop, inrunners could shed a magnet with no prop, when turning at 20,000 RPM or more. (Read the motor manual on this!)


Hopefully this info will useful to some of the readers of the WattFlyer forums!



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Old 06-02-2008, 07:08 PM   #2
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Very good. Just one question.
Why not run the inrunners with no load?
Wouldn't the max rpm be limited anyway by counter ems?
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Old 06-02-2008, 10:28 PM   #3
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Yes, the inrunners would also have a maximum RPM. I've never owned one, but have read that their magnets can be subject to centrifigal force, and could come loose at extreme RPMs. Probably not a problem, but with the folks that read these forums, someone might bring this up.

This is not a problem with the outrunners, since their magnets are INSIDE of the rotating bell.
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Old 06-03-2008, 01:52 AM   #4
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You can run inrunners at no load too. Rpm will never exceed Kv*voltage.

Vriendelijke groeten Ron
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Old 06-03-2008, 02:29 AM   #5
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That makes sense, since these motors will be running at maximum RPM (Or even more because of windmilling) in a steep dive of an acrobatic model.
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Old 06-03-2008, 02:30 AM   #6
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That makes sense, since the motor will likely exceed the no load RPM in a steep dive of an acrobatic model.
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Old 06-04-2008, 01:00 AM   #7
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Kyle, I read this one in another forum: check for shorts between each phase/terminal and the stator. Use a sharp point because the stator has an insolation layer.

Maybe add the above to your first post?

In my fist post here you'll find more tests:
http://www.rcgroups.com/forums/showthread.php?t=240993


Vriendelijke groeten Ron
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Old 06-04-2008, 08:44 AM   #8
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I use a voltage supply with current limiter to quickly test ESC/motor. Without load even medium sized motors will not require more than 2-3A to start and even less to run.
You see problems fast at the current and usually the limiter will save the ESC from harm.

I got used to checking every new part (motor or ESC) right after reception before adding connectors.

RK
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Old 06-04-2008, 11:27 AM   #9
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Good article.
I am always afraid of using power supply to power the ESC, as the ESC capacitor is then the only part to catch reverse current pulses passing the ESC back to battery -
Absence of battery or even too long wires may cause capacitor to fail and consequent (almost immediate) ESC destruction.
Battery is much better power source, or use additional capacitor(s) between ESC and power supply.

I will add my experience with AXI2820/10 -
Using it at much lighter than 400W load, it started to overheat much.
Motor was old, more than 3 years.
But otherwise it seemed to work well, turn smoothly and so on.

So I did run it without prop, powered by 10.0V, and measured current consumed.
Note that it is 1100rpm/V outrunner so the rpm did remain acceptable (below 11000) and not harmfull to motor at all. Always be sure about this !

The amp draw was 4.4A , which is double more than expected, to manufacturer specs saying 2.3A at 10.0V.
Voltage measured by turning the motor by drill was OK.
So - the motor has a serious problem. Risk of burned ESC and as I am using BEC the consequent risk of falling plane was real.

As the rotor with magnets and the strength of magnets seemed OK, Manufacturer sent a new whole stator, cheap enough and surprisingly quickly, and the amp draw at 10.0V is now 2.0A (measured by HiBox). And I am happy for the almost new motor, now.
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Old 06-04-2008, 04:21 PM   #10
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That is an interesting issue with current limited power supplies. Anyone who has placed an 100 Mhz oscilloscope across the battery of a BRUSH type ESC control will be shocked as to how much electrical noise is present. Eight years ago, I designed a PicChip ESC for brush type motors, and made the dumb mistake of using a tantalum type of capacitor across the ESC input to knock off the noise. This ESC was rated at 40 Amps and 55 VDC. And that cap was directly connected across the battery input to the ESC. The danged capacitor EXPLODED when I ran up the motor at 3/4 power! It made a real mess, since tantalum capacitors use sulphuric acid inside.

The aluminum capacitors used on present day brushless ESC controls are much more capable of handling these voltage and current spikes that exist. But, the question is, with a "softer" current limited supply, could these spikes pass more of this switching noise directly into the input aluminum capacitor?

While I was still working, I had access to a 50 VDC 6 Amp current limited power supply, but after retiring, don't any more. Does anyone out there have access to a current limited supply, AND an oscilloscope to clear this issue up?
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Old 06-05-2008, 11:35 PM   #11
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Kyle, another one for your opening post
http://www.rcgroups.com/forums/showt...06#post9891206

And not 'Ron Van Summeren' but 'Ron van Sommeren' (although 'van Summeren' is quite common overhere too)
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Old 06-06-2008, 12:45 AM   #12
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Sorry about that, that's what I get for not doing copy/paste.

Kind of like Wegner and Wagner around here :o
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Old 07-17-2008, 11:12 PM   #13
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Default ESC circuit diagram needed

I want to run a three phase brushless motor (CD ROM Motor). dont know how to run that.. I've tried different controllers none of them works.. Can anyone plz send me a working ESC circuit diagram..
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Old 07-20-2008, 11:35 PM   #14
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Hope you are using a proper ESC designed for brushless motors. The standard two wire ESC's designed for BRUSH type motors will not work with brushless, and could wind up in a little smoke both from the motor and ESC.

What type ESC's are you using? FYI, I've designed my own microcontroller operated ESC controls for brush type motors. Its not a simple circuit, and brushless type ESC's are far worse. I doubt if you could buy the required parts to build a brushless ESC for less cost than to just buy a Castle Creations Thunderbird ESC.

Something I ran into while working with CD rom motors, check the part where you short circuit all three motor wires together, then rotate the motor with an electric drill. The drag should be very smooth. If not, you might have one of the phases reversed on your windings. Don't know how you could find out which one is reversed without an oscilloscope. Perhaps you could short wires one and two, wind it up with the drill motor, short windings one and three, again wind it up, then short windings two and three and try again. All three should have the same "rough running" while being driven by the electric drill.

Also, run all the tests described on the dry testing of this motor to verify nothing is shorted or open. I've built up 7 of these GoBrushless motors, all run very well with the Castle Creations Thunderbird ESC units.
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Old 09-10-2008, 05:34 AM   #15
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I have ever seen a chinese article just like yours. I would like to provide you chinese translation for this conference. I will PM you soon.
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Old 09-10-2008, 06:54 AM   #16
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Default star or triangle?

this is maybe a bit off topic, but since the thread involves testing brushless motors, the next step for many readers would maybe be rewinding a motor anyway, so im bringing it up here as its quite relevant (and the threadstarter knows what he is talking about
my situation is that my motor windings IS burnt, and i need to rewind the motor. i know it has 8 windings per coil, and wire gauge and number of paralell wires is something i can count and measure of the burnt coil so thats not a problem.
the problem is that i have no idea wether this motor is triangle or star coupled. its a three phase synchronous inrunner, more specific, the hacker b40 8 l.
if there is a general rule that all rc motors is triangle for example, or someone knows what this specific motor is, it would save me of a lot of mathematical headache to find out. mechanically, these motors is simple, but electrotechnically they are quite complex, when you start crunching the numbers :P
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Old 09-10-2008, 07:11 AM   #17
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Originally Posted by ysr789 View Post
I want to run a three phase brushless motor (CD ROM Motor). dont know how to run that.. I've tried different controllers none of them works.. Can anyone plz send me a working ESC circuit diagram..
esc for brushless is a quite advanced piece of cheap chinese electronics that involves microcontrollers and quite advanced programming, so if you dont know how to make one, dont bother. even if you get the printboard with components correct, you still got the interesting part left, with programming the controller. and all this would DEFINETLY be much more expensive than just buying a cheap small esc thats more than adequate to run a cd rom.
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Old 09-10-2008, 10:08 AM   #18
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Originally Posted by Moxus View Post
... the problem is that i have no idea wether this motor is triangle or star coupled ...
If all phases are tied together in one knot (the star-point) the motor has a star-configuration. If the end of each phase is tied to the beginning of the next phase, it's triangle.

Originally Posted by Moxus View Post
... if there is a general rule that all rc motors is triangle ...
Not that I know of.

Make sure your magnets did not die due to overheating.


Read Brian Mulder's introduction first, to get the general idea:
http://www.gobrushless.com/kb/index....01_-_Chapter_1

DIY motor building tips and tricks, checks and tests:
http://www.rcgroups.com/forums/showthread.php?t=240993

Vriendelijke groeten Ron
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Old 09-10-2008, 10:51 AM   #19
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Originally Posted by ron_van_sommeren View Post
If all phases are tied together in one knot (the star-point) the motor has a star-configuration. If the end of each phase is tied to the beginning of the next phase, it's triangle.Ron
yep, thats obvious. the problem is that the windings is a big slob of epoxy glue, and no connection points is visible exept for the 3 wires coming out of the fat epoxy cake :P and to make things even harder, i angle-grindized the slob to get it out of the iron core, so its reduced to dust and 3 smaller pieces of epoxy
so... the visual inspection method is unfortunately useless for seeing how its connected. but thanks for the tip, it would been the best way if the connections was to be seen.

and the magnets is ok by the feel of them. i have no data on it though.
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Old 09-10-2008, 06:28 PM   #20
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Moxus
"the visual inspection method is unfortunately useless for seeing how its connected. but thanks for the tip, it would been the best way if the connections was to be seen."

Just a note on "Y" and "Delta" windings on your motor. Yes, getting the original windings off the motor is a real problem if the whole thing is epoxied. That is assuming they used epoxy in the first place. If it is epoxy, many epoxys are heat sensitive. Heating up the whole stator with a heat gun will turn the epoxy into soft butter, allowing it to be removed. Use proper ventilation!!! (DO NOT HEAT THE MAGNETS !!!) It's more likely to be some sort of varnish, which is very difficult to remove.

As for the "Y" or "Delta" connections, just install the motor windings with extra long leads on the windings. Then connect them in "Y" where the ends of each winding are connected together, and the outside ends are connected to the ESC. Run the motor, noting the no load RPM, and compare this RPM to the motors specifications. If the motor is running to slow, reconnect to Delta, where the windings are connected "end to end", with NO center common point. The motor will run much faster in this configuration. Yes, the same windings can be connected either in "Y" or "Delta" configuration, resulting in vastly different performance on the SAME motor windings.

Please note that these windings do have a "polarity", reversing one winding end for end will cause trouble. A quick way to find out if one winding is "backwards", is to connect all wires together, shorting them out as per above. Then turn the motor slowly with a variable speed drill. If one winding is backward, you will note obvious "chugging" while turning the motor over. Its a matter of elimination, reversing one winding at a time and re-testing until the reversed winding is found.

I'm by no means an expert in calculating how many turns or what wire size to use to rewind an existing motor.

The hard way to determing correct number of turns in a motor is to wind up one with smaller than usual wire size, (smaller wire size is easier) then try running the motor, checking RPM. Be sure to try both "Y" and "Delta" connections for each motor wind. Now, you have a baseline for that motor and its magnets. If the motor runs at the correct speed, which it probably won't, strip out the windings and try again with a different number of winds. Note that if for example you had 10 turns and the motor turned 6000 RPM, 5 turns would be 12,000 RPM and 20 turns would be 3000 RPM under no load conditions. Once you know the proper number of turns, its a guessing game to try to find out just how much larger gauge wire can be used to fill the winding space, without going to big in the wire size, where the wire simply will not fit. Not very scientific, but it works.

Do be reasonable on the number of turns. Putting two turns on the motor while shooting for 30,000 RPM probably will result in a motor that will not run, and could cause problems for the ESC. In any case be certain to fuse the ESC with a small fuse per above before trying the ESC/Motor combination.

The same motor frame can have very different performance with the same battery, depending on the wire size and number of turns per winding. Just take a look at the Hacker A50 series motors that have many different windings available.

Good luck!
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Old 09-10-2008, 08:06 PM   #21
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ahhh =) music for my ears. reminds me about the days back in high school.
actually doing something, and understanding what you are doing, and how it works. here at engineering college, its world championship between the teachers to spin the most senseless mathmatics out of the simplest electrical setups. and believe me, they are damn good.

today, my teacher proved to me that ohms law is "(kg*m^2)/(a*s^3))/a = (m2*kg)/(s^3*a^2)".
who would understand a single bit of that if one wasnt told anything about what it was? it is indeed ohms law :S

anyway, that was off topic. thanks for the tip, and it makes perfect sense =)
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Old 09-12-2008, 03:26 AM   #22
kyleservicetech
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Moxus
Boy that brings back long ago memories, my college days go back to 1959 where if you wanted a cc (carbon copy) you needed a piece of paper coated with some sort of carbon! (:>)
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Old 09-12-2008, 10:10 AM   #23
ron_van_sommeren
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@moxus
Just to meet the natives:
ModellflyNytt forum
Modellflyg SE forum
RC-Unionen forum

Not that I want to get rid off you, after all, I'm a stranger myself here in these here parts

Prettig weekend Ron
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Old 09-12-2008, 11:11 AM   #24
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thanks for the tip ron. "modellflynytt" is a sub-division of NAA wich im already a member, "modellflyg" is swedish, im norwegian. "rc-unionen" is something i havent seen before, so i might take a look at that :P
thanks
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Old 09-17-2008, 03:12 PM   #25
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Hi everyone, this is my FIRST EVER POST, so enjoy.

I was flying my home built balsa-wood plane when suddenly the motor stopped, but i still had complete control of the plane.

I suspect the motor or the esc has blown, but the motor was not hot, and neither was the speed controller. confusing hey?

THese are my specs:
Brushless Motor Specifications


Rotational Speed

1200 (kv) RPM/V

Continuous Current

18A

Max. Current

22A

Input Voltage

6 - 14.8V

Max. Efficiency

98%

No Load Current

0.8A

Internal Resistance

98

Power360W
Motor Weight (Motor only)60g
Motor Dimensions (Diameter x Length)

28mm x 27.3mm

Propeller Dimensions

8" x 5"/ 8" x 7"/ 9" x 5"

Input Battery Types

NiCd/ Nimh/ Li-po Battery

Recommend Model

Airplane

 
ESC Specifications


Dimensions

56mm x 35.1mm x 13mm

Input Voltage

6 - 18V

BEC Output Current

5V/3A

Continuous Output Current

40A

Max. Output Current

50A/12s

Internal Resistance

0.0021mΩ

Cable Type

16 AWG (Battery & Motor)

Cable Length

72mm (Battery)
72mm (Motor)
190mm (Receiver)

Input Battery Types

NiCd/ Nimh/ Li-po Battery

Recommend Model

Helicopter / Airplane



I was running a 7x4 prop and 14.8v 900mAh lipo.

It seems unlikely that the ESC would blow since it has ample amps for my aplication.

BUT my battery leads to the ESC are a little long (10 inches or so)


My ESC has no signs of damage and still beeps etc. when i turn it on, AND it still supples power to my reciever and servos.


I briefly tested the resistance between each of the 3 leads on my motor, it gave a reading of 1.1 ohms between ALL 3 lead combinations. And this tells me the motor might be ok, since a short would change the resistance in on of the combinations (is this correct?)


SO, basically im utterly confused and dont have a spare ESC or brushless motor to test which one is broken.

What do all you experts out there think?

THANKS!
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