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Cut off woes

Old 01-04-2019, 12:23 AM
  #1  
Jack_Hammer
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Default Cut off woes

I'm flying with a 3s lipos (45c) 1300mah. These are new lipos.
Weather has prevented me from flying em for a month here in Florida. So I get the chance this morning, fly around on a ten min timer using my dx6e TX. I should be able to squeeze close to 15 minutes of hard flying out of these. But I was playing it safe with the first few flights. Suddenly the plane lost throttle and barreling towards the ground, slow response with controls for some reason and managed a moderate "thumb", belly landing. (I'm flying EPP foam, so no crash damage was expected).

Didn't seem right me at first. Walking back to the my perch, i checked for heat. Lipo was ambient temp. But the esc was quite hot despite having plenty of airflow (well I think it's plenty. Could be wrong) on the verge of stinging. So I slipped it on the charger and it had a 9.1 volt charge remaining. I should have had flight time left. Motor was very cool to touch. I checked TX (dx6e) to see if there was a voltage cutoff, I couldn't find anything related to the plane itself and I knew there wasn't. Better to eliminate the improbable though.

I went back out this evening and set my timer to 5 minutes this trip, Only this time I would fly full spectrum, cruise, full throttle vertical and cruise. Right about 4:50 she chokes and comes down to land the same. Nearest I can figure is the problem has something to do with the ESC (30amp) getting too hot. It shouldn't be because the 1875kv motor draws 24.4 amps at continuous full throttle. I only cruised at around 65-75% throttle. Buuuut.... The lipo is a 45c though.

I figure I'm cooking the esc somehow and it's shutting itself down. (in which case I can bump up to a 40amp)
Thoughts?

Last edited by Jack_Hammer; 01-04-2019 at 06:03 AM.
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Old 01-04-2019, 04:28 AM
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Panther
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Maybe try a smaller prop before anything else to reduce amps. That should give you a clear indication.
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Old 01-04-2019, 05:50 AM
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Jack_Hammer
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I'm taking one out with me in the am. Though I have moderate doubt it's an Amp issue, I'll reserve the option. Micro Dan said in an email that the motor with the 7x5 prop on a 4s lipo should draw 26 amps at full throttle continuously. Im using a 3s so as you can see I should be drawing between 18 and 26 amps max. Keep in mind that they beef the Amp numbers (admittedly) by 10% as a buffer. So if you like subtract 2.6 amps. Either way, I should not be able having the heat or cutoff problem.

From Micro Dan:
This motor is a 1845Kv version built for the APC 7x5 & 6x5.5 prop running on 3s or 4s Lipo
7 Turns, 22AWG, DLRK, Star, 14 magnet polesPerformance Data:
No Load 18450 RPM, 10V, 0.9A
,APC 7x5, 12500 RPM, ​​10.5V, 18.53A, 25oz thrust.
APC 8x4 E, 12000RPM, 21.5A, 10.97V, 30oz thrust, 45mph pitch speed.
4s
APC 7x5, , 13V, 26A, 34oz thrust.
APC 6x5.5, 13.7V, 20A, 23oz thrust
Motor Weight 34g


I think this problem is keeping the esc cool. I've widened the air scoop twice the size and reposition the esc onto its side instead it's back so airflows all around it. Then out the back by the motor
But to even know if it is a cooling problem, I'm going to fly it without the canopy first. If that works, I'll try it with the modified canopy and go from there.
At any point during this, should it cut off, feel hot, then I'll let it sit for 15 minutes to cool down and fire it back up. If she does, I know the problem is 100% heat related and the esc is sub par 30amp garbage. (then I'll curse hobby king).

Thanks for chiming in.

Last edited by Jack_Hammer; 01-04-2019 at 05:54 PM.
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Old 01-04-2019, 01:38 PM
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Just for interests sakes, I run FrSky gear and Spektrum. With the Spektrum gear I use several Orange telemetry receivers and sensors. I always tie a temp sensor to my ESCs and rarely do they get over 50 degrees celcius. I run pretty conservative motor loads so I don't seem to have problems like a lot of others have.
I don't know what you use but Orange sensors are (were) less than $2 and fit the Spektrum telemetry Rxs as well. Money well spent.
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Old 01-04-2019, 11:02 PM
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pmullen503
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Originally Posted by Jack_Hammer View Post
I'm flying with a 3s lipos (45c) 1300mah.......... I slipped it on the charger and it had a 9.1 volt charge remaining.
At 3V/cell, a lipo is exhausted. Your ESC hit LVC and shut you down as it should have.
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Old 01-04-2019, 11:16 PM
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Jack_Hammer
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Originally Posted by pmullen503 View Post
At 3V/cell, a lipo is exhausted. Your ESC hit LVC and shut you down as it should have.
I was thinking of that too at first (why I didn't harbor this idea is beyond me)
But from what I've read that not even 70%. I've read you can run lipos down to 30% (20 would start to damage em.)
But a 3s is 11.1 volts or 3.7 volts per cell.
If it cuts off at 9.1 volts or 3.03 volts per cell
3.03 isn't but 20% used.
So this LVC doesn't seem right.

5min flight time is preposterous.
I've run a different motor,same kv with different esc (25amp) and gone 10 min of extremely hard flying. I switched to a Micro Dan because the other motor was running way too hot whereas the Micro Dan is always cool to the thouch
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Old 01-04-2019, 11:35 PM
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Crap! My bad! (I hate thinking in Reverse)
You're 100% correct!
I wasn't thinking volume (mah). I'm running a 1300 mah battery.
I need to upgrade to a higher capacity.

I'm sorry everyone. I'm not a stupid person.... Honestly. (but I sure do feel stupid)
You can't call a guy who planted a flag on Mars then invented the question mark "stupid"

Last edited by Jack_Hammer; 01-04-2019 at 11:57 PM.
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Old 01-05-2019, 12:02 AM
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pmullen503
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Get yourself a watt meter. Then you'll know what a particular motor and prop combination is drawing. Makes it much easier to troubleshoot a power system.

Remember, if you have 3V/cell at rest the voltage under load is much lower. I like to come down with 3.7-3.8V/cell at rest. Besides not having to storage charge my batteries at the end of the day, I know I'm not over taxing my batteries under load. It's cheaper to buy an extra battery or two than to have to replace them by running them too hard. Especially when the difference is usually just a couple extra minutes flight time.
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Old 01-05-2019, 12:17 AM
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Originally Posted by pmullen503 View Post
Get yourself a watt meter. Then you'll know what a particular motor and prop combination is drawing. Makes it much easier to troubleshoot a power system.

Remember, if you have 3V/cell at rest the voltage under load is much lower. I like to come down with 3.7-3.8V/cell at rest. Besides not having to storage charge my batteries at the end of the day, I know I'm not over taxing my batteries under load. It's cheaper to buy an extra battery or two than to have to replace them by running them too hard. Especially when the difference is usually just a couple extra minutes flight time.
Maybe I should see my Dr about getting some ANTI-BF (brain fart) meds too.
I have 3 of the gens ace 1300 lipos. I'll set my timer to 3.5 minutes instead of 5. I'll get a couple more. I'm thinking about getting two 1550's. Any more gets the weight higher than I want, reducing acrobatic ability as well as messing up the CG.
I had a watt meter at one time until I was stupid enough to loan it at the range. They drove off and never showed their face again. Just didn't remember to replace it.

Thanks for the tips and advice. You can have one (only one) beer now.

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Old 01-09-2019, 10:56 PM
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Well, after I did two small mods to help the esc keep cooler, the winds calmed down nicely enough to take her out.
I set my timer to 4 minutes flew hard. Esc was a lot cooler. Not hot but nice and warm. I didn't think to check voltage through the charger, so I put another lipo in and flew hard to see when the LVC kicked in.
I got another 4 minutes before LVC kicked in. So instead of 4:50 when the LVC would kick in I got 8. So now I can set the timer for 7 minutes and be safe.

​​​​​​Watt/volt meter on order just the same.

Watt (pun intended) I don't grasp, is how high heat in the esc could drain the lipo 4 minutes earlier? Additional draw needed to do the job?
Now one thing I still don't like is the LVC cut off. It seems too hard. The plane barely has enough to control the servos, but they do respond.
Guess I'm going to have to get a program card.

Last edited by Jack_Hammer; 01-09-2019 at 11:24 PM.
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Old 01-09-2019, 11:43 PM
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Heat can be caused by resistance therefore creating more current draw. Smooth the flow, less resistance less current.
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Old 01-10-2019, 03:37 AM
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Originally Posted by Panther View Post
Heat can be caused by resistance therefore creating more current draw. Smooth the flow, less resistance less current.
Dang I did forget to mention that prior to the yesterday's first flight, I did a short flight before the winds were supposed to kick up. I had to tweak the expo a tad so I landed. When I went to go back up, the motor jittered and fluttered without a full turn. So I took it back to the house to check connections.
I've experienced this problem once on a different model some years back so I knew there was a connection problem, most likely between motor and esc.
On checking, sure enough one of the motor wires came out of the solder with ease. The only thing that was holding it in was compressed wire into the bullet connector.
Why did it fail? The motor came with clear coated wire (with outside blue plastic coating).
It was the only wire I obviously forgot to scrape the clear coating clean with a blade. Flux doesn't cut through that thin coating of course. That had to be the source of the rapid drain and heat. Too much juice trying to get pushed through one tiny point at the end of the wire, not around it. Heat was the result.

​​​​​​Now it all makes sense. Just one undetectable, bad connection.
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