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PostPosted: Sat Feb 25, 2012 10:21 am 
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Joined: Fri Oct 14, 2011 8:12 am
Posts: 101
Location: Eagle River AK
The question I am looking for an answer to is:
If i am running too much current through my motor--or, in other words, if my motor is drawing too many AMPs--could this cause my plane to fall from the sky?

The motor seems fine and/but the plane has little glide, so if the ESC cuts power to the motor to save the motor the plane would enter a ballistic trajectory.

I believe that the ESC on my Guppy (plane) cuts power to the motor under some conditions--e.g. over current (too many amps for too long). The AMP capacity of the ESC is not being exceeded.

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PostPosted: Sat Feb 25, 2012 2:10 pm 
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The motor doesn't have any protection. It will get hotter and hotter until it fails (a winding fries.) So if you run your motor too hot you could have a failure. The best way to test this is to run the motor on the ground and make sure that it's not pulling more amps than rated for. Another way is to do a few short flights working it hard at full throttle then check to see the motor temp.

The ESC may have over current protection, thermal protection, and/or as battery voltage protection depending on the esc. When the protection kicks in the speed control will either stop, lower the throttle, or pulse the throttle, again, depending on the ESC.

I have been using ZTW speed controls lately. They offer the following settings/features:

Low Voltage Cutoff threshold: 2.8v, 3.0v, 3.2v per cell.
Low Voltage Cutoff type: Reduce power/Cutoff
Automatic cutoff when the ESC goes over 230F.

So I normally set for 2.8v per cell since I would rather use a timer and don't want the ESC to cut power when I would rather destroy a battery than the model. I also use reduce power instead of cutoff since I don't want to deadstick in a 3d situation.

So to answer your question, make sure you have correctly sized your motor and esc for the prop you are running, then make sure you have some airflow over the esc, battery, and motor, and you should be just fine.

schu


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PostPosted: Sat Feb 25, 2012 7:02 pm 
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Joined: Fri Oct 14, 2011 8:12 am
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Location: Eagle River AK
thank you schu.
from your answer i understand that ESCs do not typically (or ever) monitor the load on a motor (e.g. by accessing change in resistance).

i have some planes on which i put gear that after taking a second and more informed look, are not appropriately matched.
i am also trying to rule out causes of failure to determine what is happening with one of my planes that i am repeatedly crashing. i have fixed 2 (no i think it is three) problems so far, but i do not wish to crash it for reasons that i can work out in advance.

using propCalc it looks like i am exceeding the motor specs in two cases and possibly the ESC specs as well for one setup.

thanks again for the elec rc primer/session at AHH.
-Steve

ps when looking for a motor is it (not) appropriate to start by looking at/for desired Kv and watt ranges for a given number of cells (2s, 3s, ...)? i get funny looks when i ask for/about motors using these criteria. maybe i just deserve funny looks in general.
For example: i want a motor with a Kv between 650 and 900 that can generate approx 275 watts when using a 3s lipo .

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PostPosted: Sun Feb 26, 2012 9:27 am 
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Joined: Sat Jun 04, 2011 8:54 am
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A watt meter is your friend here Steve. You can get one cheap at Hobby King. You can then do a ground test and see exactly what your motor/esc/battery/prop combo is doing. If you are going to fly electric I think it's an invaluable tool.

Mike

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PostPosted: Sun Feb 26, 2012 10:33 am 
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Joined: Fri Oct 14, 2011 8:12 am
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Location: Eagle River AK
thx
I do have one, and use it. propCalc helped since I was forgetting or ignoring the amp limits on the motors -- since I have never fried one.
I also should start a notebook for data. _

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PostPosted: Sun Feb 26, 2012 2:30 pm 
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Joined: Fri Mar 21, 2008 2:52 pm
Posts: 643
Location: Anchorage Alaska
Steve, an inexpensive infared temp gauge is handy for quick checks on motor, ESC's and battery temps especially if they're not easily accessable. Just aim it at the object you want to measure the tempature and push the button. I bought the one pictured below from Tower.

http://www3.towerhobbies.com/cgi-bin/wt ... XEMG5&P=SM


Attachments:
Temp Gauge.jpg
Temp Gauge.jpg [ 22.75 KiB | Viewed 3523 times ]

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PostPosted: Sun Feb 26, 2012 4:58 pm 
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Steve,
What exactly are you running and what readings are you getting on your wattmeter? The more info you give the better we can help you...
J


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PostPosted: Sun Feb 26, 2012 5:09 pm 
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Joined: Fri Oct 14, 2011 8:12 am
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Location: Eagle River AK
i was mostly just asking about ESC and/or Motor "protection functions"--existence and what they do.

schu did answer the questions.

I appreciate the responses and the help offered; all is good for now.

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PostPosted: Mon Feb 27, 2012 12:56 pm 
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Steve, if you ever need more help shoot me an email at schu@schu.net

I can meet you at the field and look over your stuff if you think that will help.

Also, what happened to that other fellow that was at the clinic? I spent a bit of time getting him all setup, but I never heard how his airplane did.
schu


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PostPosted: Mon Feb 27, 2012 1:44 pm 
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Joined: Fri Oct 14, 2011 8:12 am
Posts: 101
Location: Eagle River AK
thank you schu.

I need to reach beyond my grasp or i will not get as much traffic on my YouTube channel.

I remember you working with him and i observed and picked up bits of additional info--and hopefully put it together to have some knowledge, but i have no idea who that fellow is. If i see him again i might recognize him, but quite possibly not. I do not recall seeing someone, that i am not at least familiar with, flying a plane of a style like the one he had/has. Maybe in the spring we will see him again.

My recollection is that he was between 25 and 35 years old, had brownish hair, medium to light build, and was taller than me (i am 5'11"), and might have been wearing a blue coat. Rather than being useful, this description will likely demonstrate the faultiness of my eye witness identification ability. Maybe he will see this post and get a good laugh and then give you a update.

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