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Old Jan 06, 2013, 08:13 PM
Koo
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My NTM 3000kv motor seems to have a ton less power than it used to. Why?

I have this NTM motor that I use on my radjet. I use a 5.5x4.5 prop with a HK 60 amp ESC. I've used both 4s and 3s LiPos.
I used to be able to fly my radjet with 1/2 throttle using the 3s and have unlimited vertical and I remember the crazy sound the plane made on full throttle. Very high pitched and it sounded awesome Sorry, haven't done any watt meter tests.

Now, couple months later, the motor seems to have a problem providing me even with enough thrust to fly. With a 3s I couldn't get unlimited vertical on full throttle and using a 4s, it still was struggling. Yes, it is winter now but even indoors the crazy sound the motor once made isn't that high pitched.

Any ideas why it would be like this? To be honest, I haven't done a throttle calibration for awhile and I don't have any measurements except for my feel of the plane and motor. Thanks.
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Old Jan 06, 2013, 09:17 PM
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Have you over-cooked it?... maybe over-heating has de-magged it to some degree.
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Old Jan 06, 2013, 11:32 PM
Koo
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I'm almost positive I haven't. The only times I've used it with 4s have been after it started acting up, and with a 3s, well, my LiPo or 60 amp ESC would die before the motor. And after each run, the motor hasn't been hot, just warm.
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Old Jan 06, 2013, 11:55 PM
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Wattmeter. Get one. Use one.

Have you been flying the plane for the past couple months, or has it been sitting around doing not much of anything? If that's the case... Did you happen to charge the batteries up after you last used them and then put them on a shelf for a few months?
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Old Jan 07, 2013, 05:11 AM
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with a 2800kv in my FJ Im around 60 Amps in air, sometimes more like 70A...with the same prop as you... so I guess a 3000KV motor could be as much as 80Amps,,,, you could have fried it, the magnets...

Cant think of another reason of motor suddenly lose power, except the bearing gone bad totaly, but that you could feel by turning it by hand..
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Old Jan 07, 2013, 12:46 PM
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It is necessary to know that these real voltage by applying to your engine, to differentiate between motor or battery failure.

At 4s your engine is seriously abused.
But your batteries also.
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Old Jan 07, 2013, 03:52 PM
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If we apply the 3w/g rule of thumb to your 87g motor we get about 260W... that's 25A or so on 3s, and less than that on 4s! Most motors can safely dissipate about 1W/g-1.5W/g of waste heat... if you are pulling >60A at 75% efficiency... that is a LOT of waste heat.
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Old Jan 07, 2013, 08:01 PM
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Rad jet has tons of air cooling for the motor.

My vote is for "dead Lipo". I'd say your lipos are used and abused and dead and can't pull the high 'c' it once did.

same thing happened for me on my stryker. After 3+ years, my stryker stopped screaming and I sorta got used to it. Then I bought some 40c Lipos and that thing is screaming again.

Like others have said, buy a watt meter and crank it up and watch the voltage drop when you WOT. Chances are you're dropping wayyyyy down when you WOT.
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Old Jan 07, 2013, 09:45 PM
Koo
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Quote:
Originally Posted by C₄H₁₀ View Post
Wattmeter. Get one. Use one.

Have you been flying the plane for the past couple months, or has it been sitting around doing not much of anything? If that's the case... Did you happen to charge the batteries up after you last used them and then put them on a shelf for a few months?
I charge the batteries couple days before flying. I've used 3 different 2200mah 25c 3s nanotechs, all with the same result.

@all others saying that the heat has killed the motor

I realize that I have a too large prop but I have been very careful with my throttle. The radjet was too quick for me at 3/4 throttle using 3s and I've only gone to 4s after I realized that there was a problem with power.
I'll buy a watt meter because it seems like a must-have tool.
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Old Jan 08, 2013, 12:13 AM
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This motor to 32600rpm consume 69A, 1000watts minimum.
Is necessary battery over 2650-3000ma.

If the Kv is larger, then the scenario is worse for the engine.
It is very common that these engines have one greater than advertised Kv.

In an atmosphere of much air flow, with low capacity batteries, motor can consume 600-800 watts.
Still will not last long and the batteries either.

I also believe that in this case the batteries are the first problem.

A full charged battery, discharged at 20C should be given at least 3. 66V by cell after 30 seconds.
Otherwise, the battery may be exhausted.

To 3s Llipo the correct propeller. 38A and around 24750 for 400 watts of consumption.
less than 5 watts per gram.
Engine will not last throughout life, but will serve for many flights 1 or 2 seasons.

Nanotech batteries give many problems download above 23 c.
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Old Jan 08, 2013, 12:44 AM
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I don't think the motor's high Kv value is as much of a problem as it seems.

I flew a lot of flights with a TowerPro 3850Kv heli motor (actual Kv was more like 3500 according to Jacko) on 3S packs and APC 5x5 or 4.75x5.5 props. It would draw around 51A static with either prop and hit upwards of 550W (~10.9V) on the ground, but the prop would unload a whole lot in the air. I don't have any in-flight numbers, but based off similar systems I might easily have been below 40A WOT in flight.

All components would come down cool or just slightly warm. It might sound very much "against-the-rules", but nothing in that system was being pushed harder than it could handle. This effect isn't isolated to that one setup, either. I've noticed that most drive systems on the ragged edges of what's conventionally considered "safe" will often tend to be less hazardous than they seem.

The 3000Kv NTM motor is around the same size as mine. Even allowing for a 15% variation in stated Kv, it would still be "less motor" than what I was running. I think the 5.5x4.5 prop is a fairly reasonable 3S choice for that motor in a RadJet.
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Old Jan 08, 2013, 08:12 AM
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Koo29,
The surefire sign of a motor with "shot" magnets is a very hot motor after flying. If you can touch it after landing or use an IR temperature meter, check out the temp. Be careful, if it is case of weak magnets the motor will be hot enough to burn your fingers.

Might need some oil on the bearings?

Can you measure the voltage of the packs?
What is the voltage of the packs after flying?
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Old Jan 08, 2013, 08:33 AM
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If the Kv is larger, then the scenario is worse for the engine.
It is very common that these engines have one greater than advertised Kv.


Interesting that you should mention this, Manuel. I tested a Turnigy 2836-2350 motor (essentially = NTM) and it came out at ~2800Kv. I wonder what the Kv of this 3000 really is?
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Old Jan 08, 2013, 12:01 PM
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Brucce Abbot, says that until the +/-10% difference can be found in an engine


It is good to test the engine before use, and measure the Kv.

With this problem, would only be necessary to measure and should be more high,
show my an engine with demagnetization by heating problems.
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Old Jan 08, 2013, 12:07 PM
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Quote:
Originally Posted by manuel v View Post
show my an engine with demagnetization by heating problems.
Agreed! I think before a motor gets demagnetized, you'd burn up the motor's winding. anyways, as said earlier, I still think this is a 'dead lipo' issue.
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