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Power Systems Talk about motors, ESC speed controllers, gear drives, propellers, power system simulators and all power system related topics

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Old 08-03-2018, 06:42 PM   #1
Keyser Soze
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Default Hot ESC !!!

Hi all !!


I converted an Aerostar 40 I built 30 years ago to electric. Flew without a trim adjustment when I tried it last week. Here's the thing.


I'm using an NTM Prop Drive 35-48 V2 Motor, HobbyKing 60A ESC (5.5V 4Amp) ,a 3300 4cell Lipo (35-75C) and a 12x6 electric prop. I mounted a hood scoop on the front that points directly on to the esc.
I landed after 7 minutes at 1/2 throttle or less, and that thing was so hot I could not touch it for 5 minutes. I thought it was going up in flames. I do not want to risk losing this old plane to an overheated esc. Oh, servos are the old style Futaba std servo with new ends on them, and I was using elevator and ailerons mostly to make right turns, (one loop too ).
I just got back into this plane after about a 29 year delay, so I really don't want to mess it up. If it's my fault as a pilot, ok, just not a glitch.


Any ideas anyone?


Thanks
Eric
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Old 08-03-2018, 07:26 PM   #2
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Hi ... welcome ...

eCalc is your friend here .... suggest for the few $ its well worth it ...

I put TGY 3548 vs 1100KV .... 4S 3300 LiPo and it went off the scale for Watts !!

Please give more info such as the KV of the motor ... even on 3S the 1100KV motor is pushed to limits on this ... the 900KV motor is better on 4S ...

Seriously ... register with eCalc ... its a model flyer who has created one of the best calculation programs to help us decide motor / battery / ESC / Prop combos ...

Nigel

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Old 08-03-2018, 11:13 PM   #3
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Get an inline wattmeter. They are essential for understanding what is going on in an electric airplane.
They will show you; The running voltage, the current, the watts going into the motor, and the amount of mah you have pulled out of the battery.

IE if you ran the motor for 5 minutes at maybe 75% throttle it will give you the amount of battery power used then you can compare to the total capacity of the battery.


They will show you the effect of different props in real life, I know eCalc, is good, but I like to see what is happening in MY airplane.


Sounds like you had too much prop causing too much current.


The reviews are showing one guy running a 4s battery and a 12x6 prop getting 734 watts.
Another guy running a 4s battery and a 12x6 prop getting 830 watts.


This shows me that the second guys battery is in better condition and holding the voltage better. Plus we don't know if they are running the same 12x6 prop. There are vast differences between different brands and shapes of props.


Good luck, keep us in the loop.
You don't want an ESC blowing up in the plane,
Don't ask me how I know that one.

Dave R, KI7MTA Proud PGR rider.
When you have flying skills like mine,
You become a master at repair.
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Old 08-04-2018, 12:25 AM   #4
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I run a 3548 NTM propdrive on a 55 Amp Turnigy Trust ESC with a 12x8E Prop on 3S and never had the ESC more than slightly warm.
It has also run on a 12x6 Master airscrew 3 blade gas prop with no problems as well.
Have you checked the timing?
Try it on a 3S. Maybe 4S is pushing the limits of that ESC.
As Wildflyer says, a wattmeter will tell you everything.
I find the Hobby King HK-010 power analyser to be excellent.
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Old 08-04-2018, 08:21 AM   #5
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Have to agree ... a Wattmeter is the friend in hand.

Nigel

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Old 08-04-2018, 03:50 PM   #6
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Without a watt-meter you are in the dark, until something starts to glow

Vriendelijke groeten Ron
Without a watt-meter you are in the dark, until something starts to glow
e-flight calculators watt-meters diy motor tips Cumulus MFC
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Old 08-04-2018, 03:57 PM   #7
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Originally Posted by Keyser Soze View Post
... that thing was so hot I could not touch it for 5 minutes. ...
What part of the controller was hot?
The power FETs/workhorses? Always 6, 12, 18, ...) of them in a brushless controller.
The barrel shaped input capacitors? Electrolytic_capacitor (wikipedia)




Vriendelijke groeten Ron
Without a watt-meter you are in the dark, until something starts to glow
e-flight calculators watt-meters diy motor tips Cumulus MFC
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Old 08-04-2018, 03:58 PM   #8
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Or the BEC (battery eliminator circuit)?


The higher the battery voltage, the hotter a linear BEC will get, for a given current/load/servos.
In other words ...
The higher the battery voltage, the lower the current a linear BEC can supply. Does not apply to switching BEC (SBEC).
In depth:


Vriendelijke groeten Ron
Without a watt-meter you are in the dark, until something starts to glow
e-flight calculators watt-meters diy motor tips Cumulus MFC
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Old 08-04-2018, 05:50 PM   #9
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Default Thanks

I'm going to order the watt meter today. The motor is an NTM 35-48 900 kv, Max values according to specs are 815 watts, 15v and 55 amps. The prop is a 12 x 6 e prop ( I think a Master Airscrew) with pointed ends. I had an idea that maybe a 3 blade would be better, and I have one, but I may be able to use a 3 cell instead. I could also install an 80A I have. I need the watt meter. I will also get the calculator. I hate the idea of wrecking any equipment if it is so easily prevented. Till it gets here though, would less voltage be able to get this plane off the ground? I'm not sure I take off well enough for that.
( I have a 100 ' landing area and a 20' take-off pad). I usually (Carrier) Launch it , full throttle, full elevator at the end of the driveway and up ( or not) over the field. Grass around the cut area is 4' high so missing the LZ is messy, but soft enough.



Thanks everyone for the great advice,



E
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Old 08-04-2018, 05:52 PM   #10
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If the ESC he is using is the standard Hobby King 60A with 4A BEC ....



This has SBEC and is not linear. Most ESC's over 35A are switche mode BEC except for a few such as the old square Hobby King 50A job ...

Nigel

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Old 08-04-2018, 06:09 PM   #11
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mmmmm eCalc ... https://ecalc.ch/motorcalc

With 3S - gives marginal thrust to weight ... she'll fly but will need throttle ... the type of model will help here being a trainer high wing job. Yes its do'able. But no yanking her of the ground ... she needs to 'fly'

With 4S - this is good BUT not too happy with that power reading .. shows the motor going into the red ... strange as I would have thought a motor like that would be fine on a 12x6 ..

I have attached the two print-outs 3S and 4S from eCalc ...

Nigel


Attached Files
File Type: pdf Aerostar 3548 3S 12x6.pdf (320.6 KB, 3 views)
File Type: pdf Aerostar 3548 4S 12x6.pdf (333.1 KB, 2 views)

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Old 08-04-2018, 06:27 PM   #12
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Default That is it

Yes that is exactly the one. In the Item description it says UBEC and on the part it says SBEC. In the downloadable instructions, it is listed as SBEC also.
If it is the BEC part that is overheating would newer smaller servos be an advantage?
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Old 08-04-2018, 07:29 PM   #13
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Originally Posted by Keyser Soze View Post
Yes that is exactly the one. In the Item description it says UBEC and on the part it says SBEC. In the downloadable instructions, it is listed as SBEC also.
If it is the BEC part that is overheating would newer smaller servos be an advantage?
Ignore it ... its not the BEC ... UBEC and SBEC are just different terms for same ...

Your hot ESC is the actual motor part as it is in a closed box - you mention a scoop - but does the air have an exit ! With no airflow ... and its working at near max ... eCalc shows it working about 53A ....

It is normal that we would fit an ESC that can handle 1.3 - 1.5x the max current expected ... therefore for your set-up I would be looking at a 70A ESC or more.

Your servos ... what are you using ? Old originals or new ones ?

Nigel

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Old 08-04-2018, 10:06 PM   #14
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Try the 3S just taxiing for a start. I think you won't be disappointed. I don't even buy 4S batteries any more.
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Old 08-05-2018, 06:53 PM   #15
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Yep ! Sorry, I have a lot of venting out of the bottom under the original servo tray, so I did not add more. It does blow a bit out the bottom. The servos are the old ones from 30 years ago with new ends. I'm going to try the 3 s and then if all goes well, I'll try the 80a esc and go back to the 4s. I only have 1 4s so the flights are only 7 minutes and then an hour to wait. 3s I have a dozen others, so it would be better.
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Old 08-05-2018, 10:03 PM   #16
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I ran full sized futaba servos that I actually cut the connectors off of and soldered on new leads to use a spectrum receiver. This was on a nitro .25 sized ugly stick my grandpa built in the 80's at some point. The old servos used less power then the 9gram servos I was using in my slow sticks.

All things being said, use a ubc or a good switchmode setup with a plane of that size. Being as its old and probably sentimental, you don't wanna lose it to a cheap esc.

slow stock prop reversal. it flies! easily! 543 watt dual motor bipe slow stick. push-me-pull-you. 242 watt 3 channel slow stick. 365 watt mini ultra stick. 415 watt mini contender. 810 watt ultra stick .25e. 220 watt alpha 450 sport (retired).
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