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Old Mar 13, 2002, 11:09 AM
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United States, IN, Evansville
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Kontronik 50-6-18 / Motor cuts out

I have been flying my converted Kaos for a little now. But I have just started having problems. For some reason the motor keeps cutting out right before I get to full throttle.

I put a wattmeter on it and the amps are at about 36 when it cuts out. The volts are down too about 16 or 15 volts when it cuts out. (This is for a fully charged pack)

The undervoltage protection is .8 volts per cell. I am using 16 cell packs so that would not cut in till 12.8 volts.

Does anybody know what a 16 cell pack voltage should be down to at say 45 or 50 amps? (That is about the amp draw with the 12x10 prop).

Possibly my cells have gone bad? They were cells that vented but I emailed with some very reliable sources who said to just keep using, and I may see reduced capacity...

Or could something be wrong with the ESC. Does anybody else have this ESC? The manual says this could happen from Radio interferance or Over heat protection cutting in. It is definately not Overheat protection, its not even warm with it cuts out. It says it could be a loose connection but I think all those are good.

Thanks,
Kenny
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Old Mar 13, 2002, 12:15 PM
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Kontronik controllers also have an RPM limit. When you reach this the motor cuts.

What is the Kv of the motor you are using, then multiple this y 1.2V to see if you are near the 50,000 rpm limit

This happened to me when I wanted to run my F5B 10 cell motor with a smaller prop and lower current draw.

Paul
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Old Mar 13, 2002, 12:55 PM
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The motor is the Mega AC 22/30/2.
1770 rpm/V
2.6A idle
.014 ohm

The rpm/V is 1770. So with 16 cells the voltage would be about 21 volts on a charged battery. So that would be 21*1770 which would be just over 37,000 rpm. But moto calc says it is much less than that. Moto calc esimates about 27,000.

The Kontronik Manual says its 50,000 for 4 pole motors, 25,000 for 8 pole motors, and 100,000 for 2 pole motors. What does that mean?

Why would this just start happening? I have flow probably 15 flights so far without this happening. They were with a 13x10 prop but I can't imagine the 12x10 increasing RPM that much.

Thanks,
Kenny

Possibly the Pinion could be slipping or something causing the motor to spin more RPM. I seriously doubt that....
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Old Mar 13, 2002, 01:49 PM
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Hi Kenny,
I think the problem is due to the rpm limit of the controller.
The Mega is a six pole motor and therefore the rpm limit is somewhere between 25 and 50000 (probably in the 30's K rpm).

To confirm this, put the controller to mode 5, which will set the rpm limit 'as high as possible' according to the manual. The timing will be more advanced and therefore a higher rpm will be possible.

Note that the undervoltage cutoff will also be disabled, as well as all the safety features so just use that mode 5 to identify the problem.


If that is the case, then the solution will be to prop the motor for a bit less rpm, but if you want the same power level then the current will have to go up a little. Then, you will see if the cells are a limitation or not (needs to be put back to mode 1 for that, assuming you were using mode 1 to start with).

Kyri
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Old Mar 13, 2002, 01:52 PM
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I read somewhere about the Mega motors being 6 pole motors.

Would that mean the Smile controller may be limiting the RPM to some where between 25k and possibly 30k for the 6 pole motor? It would definately be up near that RPM.

Bummer, if this is the case then I either need to get a different ESC, or get the 22/30/3 which is a lower Kv.

Kenny
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Old Mar 13, 2002, 01:53 PM
BEC
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Kenny,

Megas are 6 pole motors, so you may very well be hitting that RPM limit......based on what you've posted the 6 pole limit would be 37,500.
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Old Mar 13, 2002, 02:14 PM
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I think you guys are right. And you want to know a really interesting thing. Since I live here at altitude it seems that the barometric preasure change a lot. I think the other day when I was flying with the 13x10 the same thing happened. I am betting that the barometric preasure dropped a bit putting me over the threshold. I will do some testing tonight.

Now watch the air preasure go up and I not be able to reproduce it. Another factor is that the flying field is a little higher than where I live....

I will probably have to go with the /3 turn motor. Or get a new ESC. Or do all ESC motors have this RPM limit?

BUT I just don't see how I could be going over 37,000 RPM. Motocalc is predicting about 27,000 rpm and I doubt it would be that far off. I know its an estimate but its usually in the ball park...
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Old Mar 13, 2002, 02:28 PM
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During certain types of flight pattern, in particular pointing the nose down with full throttle will cause the prop to unload and spin faster, even if it was OK on the ground. The lower air pressure will certainly not help either. These variables explain why you haven't always had the problem.

Maybe a cheaper solution is to use a slightly bigger prop? More diameter will limit the rpm a little, and since the situation is marginal it may just do the trick. You will have more thrust, and you can always throttle down a bit to maintain flight times. More pitch would also limit the rpm but will cause the current to rise a bit less than if you increased the diameter.

Your esc should be capable of 50A continuous, and bursts of 70A or whatever it says in the manual - so use that capacity at the expense of some rpm and all you will have to buy is a prop!

Kyri
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Old Mar 13, 2002, 02:31 PM
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Quote:
[i]The Kontronik Manual says its 50,000 for 4 pole motors, 25,000 for 8 pole motors, and 100,000 for 2 pole motors. What does that mean?

Why would this just start happening? I have flow probably 15 flights so far without this happening. They were with a 13x10 prop but I can't imagine the 12x10 increasing RPM that much.

[/B]
It means 50,000*4 or 200,000 strokes per minute is as fast as the microprocessor can stroke the motor. So 200,000 / 6 = 33,333 is the maximum RPM you can achieve with a 6 pole motor. You aren't anywhere near that unless your prop RPM is over 10K which it isn't.

Depending on pack construction and whether it is hot off the charger or not the volts per cell could be anywhere from .8 to about 1.15 (only briefly this high). I would consider .9-1.0 normal for 45-50 amps a minute into the discharge. so 14.40 - 16.0 volts.

Try mode 5 and see if the problem goes away. If that fixes it the problem is not the RPM limit but the soft timing combined with very high RPM's and a limited angular difference between poles on a 6 pole motor. Competition mode has more advanced timing.
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Old Mar 13, 2002, 02:55 PM
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With a 13x10 prop geared 3:1 I am already pushing the 60 AMP cut off. On the ground its static draw is about 56 but sometimes right from take off if I were to go straight up for a while the over amp cuttoff would cut in. Thats the reason I went down to a 12x10. Its not that big of a deal and throttle management takes care of it. I just don't want to risk damaging the ESC with too much current.

its only 50 amps (60 amps for 15 seconds). Can I rely on the protection circuits and just prop for say 60 amps or more or will this destroy the controller? Its got plenty of cooling. Problem is in the summer time the air pressure will go down even further making the RPM go up even more.

I guess I could go down to 15 cells...

Oh, also I bet I am up near 10,000 RPM if not over. You would be amazed how much more RPM a prop will spin at 7000 feet elevation. I will tach it out tonight.
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Old Mar 13, 2002, 03:08 PM
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Yes, going to 15 or even 14 cells should do the trick in that case. Your voltage drop under the (lower) current will be lower, the max rpm of the motor will be lower, and you may even be able to go back to that 13 inch prop and have no problems.
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Old Mar 13, 2002, 03:15 PM
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This may be a bad or wierd idea. But could I also just move the end point adjustment for my throttle to like 75%? The plane has so much power with the 13x10 anyway. Probably a poor solution...
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Old Mar 13, 2002, 03:38 PM
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That will only be a solution if the full throttle current does not exceed 50A. Otherwise the capacitor on the esc may blow due to overheating at part throttle settings. (The resultant aerobatics that follow due to interference caused by the damaged esc may be hard to control )

The best solution may therefore going to a higher current rated controller so that you can get the same power by using a bit more current on a few less cells, and stay away from the rpm limit that way.

Or, live with less powerful climbs after take off by using a cell or two less on your existing setup.

Kyri
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Old Mar 13, 2002, 03:53 PM
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Cool,

Thanks for all the input guys. My testing tonight will hopefully confirm the consensus of everyone here. Would the Jeti 70 AMP controller be high enough? The reason I went with this one is because nobody had that one instock and the vendor was nice enough to give me a really good deal on it since he did not have the other in stock.
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Old Mar 13, 2002, 05:29 PM
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OK,

I am home and I have done some testing. I put it in APM mode and tached it out. It only got up to about 8500 RPM before it quit. The volts were right around 15-16 volts. I then put the 13x10 prop and it did the same thing at even lower RPM.

THEN i put it in compeition mode and it did something even stranger. In competition mode the brake is set to full on. So when I began to throttle up no matter what throttle setting it would hit the break about 2 or 3 seconds later. Even if I tried to go up to full throttle and it would still hit the break.

Either something is really screwed up or it is in a really weird state....

I have no idea at this point. I don't see how the RPM limit could be in effect. First I have flown 15 or so flights with it flawlessly. Second it is not even pushing 30000 RPM on the motor. Not if it only cuts out at 8500 rpm geared 3:1. That would only be 25,500.

Could something have happed to either my ESC or motor? Any other ideas. This really is annoying...

CORRECTION: I did not put the 13x10 back on. Just did it and powered up. Drew 54 amps (this is on the battery I have been testing with so its probably about a minute or so into acutal flying time) and the thing did not cut in. So it must be the RPM cut in and it must be coming in at lower than 33k....

Kenny
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