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Old Jan 24, 2013, 07:56 AM
I just want to go fly!
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so are you saying that with a 54 amp esc hooked to a stock motor on 3s turning a apc 10x6 4 blade i am going to cook my motor reguardless of throttle management? thanks for the insight. walt.
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Old Jan 24, 2013, 08:38 AM
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Indianapolis, IN
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Walt the real only way to tell for sure is to use a wattmeter. I plan on using one of the HL four bladers either the 9 or 11 and simply plan to purchase the G25 710KV motor from HK, it is less than $30 shipped from the US Warehouse.
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Old Jan 24, 2013, 09:08 AM
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United States, MI, Grand Traverse
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Originally Posted by walter3rd View Post
so are you saying that with a 54 amp esc hooked to a stock motor on 3s turning a apc 10x6 4 blade i am going to cook my motor reguardless of throttle management? thanks for the insight. walt.
No its not the amp rating of the ESC, it is the max amps the system (Motor Prop ESC battery) is capable of producing. Whatever you get by a WOT static run on a watt meter is close enough. Just be wary that you can not reduce throttle to get a lower number on the meter and think it is safe.

Real life example: The completely stock jug but with a Extra 10.5x9 prop.

If you hook up the amp meter and do a static full throttle run with a good quality battery you'll get around 33 amps. Changing the ESC to a quality 60 amp unit will not change the amps because the ESC has nothing to do with the power demand of the motor. The system will be safe. Now lets say you grab one of those 11x10x4 Hobby lobby props. You get another fresh charged battery and try a WOT static run. You'll get a reading of 55-60amps, maybe more! say you throttle back to 1/2 and see the amps around 30. Even though the average amps at 1/2 throttle is reading 30 the components are seeing 0-60-0-60 over and over and are not going to last.
I guess just remember that a watt/amp meter is giving you the average amps it is using as it does not have the sub-millisecond resolution to actually show what is happening. You should test at full throttle and make sure every component in the chain can handle that number.

-Brian
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Old Jan 24, 2013, 09:41 AM
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Originally Posted by walter3rd View Post
so are you saying that with a 54 amp esc hooked to a stock motor on 3s turning a apc 10x6 4 blade i am going to cook my motor reguardless of throttle management? thanks for the insight. walt.


walter the only way to find out is to set your system up.. hook the battery to the watts meter whereit says "source" and then the watts meter agin to the ESC.. run your system, gradually go all the way up to WOT.. foe a few secounds.. see whats the highest AMPS draw... if it goes past 40 amps.. i do not recommend it... Why because only if you are robot and can program your self to not go WOT anytime during the flight then i would recommend it.. can you get away with it? Yes.. is it possible you can burn up the motor during flight? Yes.. Can you loose your money loosing your plane? Yes. it is all possible.. but if you have a set up that wont go past the motor specs.. then most likely youll loose your plane due to something else before the motor burns up this motors the 15e its the same one i have on my apprentice, and it took like 2 years of abuse flying almost everyday for the motor to start feeling cranky
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Old Jan 24, 2013, 09:49 AM
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Excellent point, I never really thought about it like that!

Just like below, I would not recommend it but you can limit the travel of the throttle channel so even if you push full throttle you will only see 3/4 or whatever you set the travel at. Again, it really isn't recommended.

Quote:
Originally Posted by kalmon View Post
No its not the amp rating of the ESC, it is the max amps the system (Motor Prop ESC battery) is capable of producing. Whatever you get by a WOT static run on a watt meter is close enough. Just be wary that you can not reduce throttle to get a lower number on the meter and think it is safe.

Real life example: The completely stock jug but with a Extra 10.5x9 prop.

If you hook up the amp meter and do a static full throttle run with a good quality battery you'll get around 33 amps. Changing the ESC to a quality 60 amp unit will not change the amps because the ESC has nothing to do with the power demand of the motor. The system will be safe. Now lets say you grab one of those 11x10x4 Hobby lobby props. You get another fresh charged battery and try a WOT static run. You'll get a reading of 55-60amps, maybe more! say you throttle back to 1/2 and see the amps around 30. Even though the average amps at 1/2 throttle is reading 30 the components are seeing 0-60-0-60 over and over and are not going to last.
I guess just remember that a watt/amp meter is giving you the average amps it is using as it does not have the sub-millisecond resolution to actually show what is happening. You should test at full throttle and make sure every component in the chain can handle that number.

-Brian
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Old Jan 24, 2013, 10:05 AM
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Originally Posted by kalmon View Post
This is completely untrue and comes from a common misunderstanding of how the ESC + motor work. The above scenario would work if the ESC varied the voltage to the motor to adjust throttle, however it does NOT!
A brushless ESC works by varying the on-off pulse time to the motor. Why is this important? Because when it is on it sees 100% power for the time it is on. Throttle management can not reduce this. Granted this on-off-on-off all happens at millisecond speeds. But while the it is in the "on" it will be drawing the max possible power it can. I.E. if a WOT amp reading on your motor+prop+battery combo gives you 53 amps, that is what the motor is drawing when it is "on". The reason the reading on the wattmeter goes down at less throttle is that the off cycle is longer, not that the motor is asking for less power.

Here would be what the motor sees over a given time period at low throttle:
0-0-0-53 0-0-0-53 0-0-0-53 0-0-0-53: The watt meter would read 13.25amps and 147 watts(assuming 3 cells) because that is the average amp draw. However average doesn't mean you motor didn't get the full 53 amps and 588 watts for that on part.

What throttle management does for the motor is help keep it from heating as rapidly as it has longer off time to dissipate heat, however it only delays the heating as the motor will eventually get to that 588watt temp and melt, if the ESC doesn't burn up from having to deal with the 53amps it's holding back 3/4 of the time(in the above example)!

Bottom line make sure every component in the chain is capable of handling the WOT amps/watts your system can produce then you will be safe. The only way to safely change this number is actual physical hardware changes. usually prop diameter and/or pitch.

-Brian
I keep hearing this about ESCs. However, I'm having some trouble believing that:
1. The amp ratings on ESCs are for milisecond pulses, not continuous (aka average) output. This seems to defy the fact that they are rated for more power over short bursts (implying that time does matter as much as instantaneous amps). If the ratings for instantaneous output, then there's no way a burst of higher power would not kill it, not matter how short the burst time.
2. There are no power supply side things on the ESCs that store additional power for use in these instantaneous bursts. This seems extremely likely, meaning that the drain on the battery would be much less the 53A, and would be approx continuous (over a scale of like a second). It's my understanding that an ESC is a whole lot more than just a relay shunting the battery directly to the motor for short periods of time. I'd like to hear from and EE on this part, for sure.
3. Heat is not a different issue altogether, and certainly time is the biggest factor in this. There's parts in the ESC that will fry instantly on too much current, and there's parts that will break when they get too hot. I haven't seen where manufacturers are defining which it is that will kill it. If it's too much heat, then it implies that the given amp ratings have nothing to do with the limit of instantaneous current sent to the motor, as in a 30A esc should have no problem putting little 53A pulses.

The point of all this is not to dispute what you're saying, but rather to solicit some sources on this. What I've said above is enough to make me seriously question that an ESC is subject to the same loads regardless of throttle settings. I'm no EE here, so I can certainly be wrong. However, I would like to see some good sources for this information one way or another.
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Old Jan 24, 2013, 10:12 AM
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Originally Posted by IndyMatt View Post
Excellent point, I never really thought about it like that!

Just like below, I would not recommend it but you can limit the travel of the throttle channel so even if you push full throttle you will only see 3/4 or whatever you set the travel at. Again, it really isn't recommended.
Limiting the throttle channel only works for some ESCs. For instance, I just put a electrifly 12A SS ESC I had laying around from an old plane in my new Crack Yak. That ESC does squat for the first 40-50% of stick travel.

I thought, ok, well I'll just put a throttle curve in the radio, and bump up the bottom end so that I get the prop turning right away. Worked great that first flight. But after I switched batteries the ESC recalibrated the throttle range to what it was seeing. I didn't notice it was doing a re-cal, and I ended up putting twice as much correction back into the curve. The third time I figured out what was going on. Essentially, ESC's that calibrate the throttle range on every power up aren't going to like your trimming, and happily ignore it.

I wouldn't count on restricting throttle to prevent a motor or ESC burn out...
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Old Jan 24, 2013, 10:39 AM
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United States, MI, Grand Traverse
Joined Oct 2008
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Quote:
Originally Posted by jtaylor996 View Post
I keep hearing this about ESCs. However, I'm having some trouble believing that:
1. The amp ratings on ESCs are for milisecond pulses, not continuous (aka average) output. This seems to defy the fact that they are rated for more power over short bursts (implying that time does matter as much as instantaneous amps). If the ratings for instantaneous output, then there's no way a burst of higher power would not kill it, not matter how short the burst time.
2. There are no power supply side things on the ESCs that store additional power for use in these instantaneous bursts. This seems extremely likely, meaning that the drain on the battery would be much less the 53A, and would be approx continuous (over a scale of like a second). It's my understanding that an ESC is a whole lot more than just a relay shunting the battery directly to the motor for short periods of time. I'd like to hear from and EE on this part, for sure.
3. Heat is not a different issue altogether, and certainly time is the biggest factor in this. There's parts in the ESC that will fry instantly on too much current, and there's parts that will break when they get too hot. I haven't seen where manufacturers are defining which it is that will kill it. If it's too much heat, then it implies that the given amp ratings have nothing to do with the limit of instantaneous current sent to the motor, as in a 30A esc should have no problem putting little 53A pulses.

The point of all this is not to dispute what you're saying, but rather to solicit some sources on this. What I've said above is enough to make me seriously question that an ESC is subject to the same loads regardless of throttle settings. I'm no EE here, so I can certainly be wrong. However, I would like to see some good sources for this information one way or another.
Sources: Castle Creations Read point 6.

1. If you read my first post it said that it would be heat that killed it most likely.

2. ESCs in general are rated for the average amps, not the short burst. Hence why most quality ESCs are like 75Amp, burst 150amps etc... And yes the ESC is more than just a relay, but I was trying to simplify it. It is actually converting the DC power from the battery to 3phase for the motor. Also ESCs all have Capacitors on them, look between the + and - battery wires on the stock 30amp.
3. Yes heat is a different issue but heat is generated faster when you have those higher energy pulses. And yes it also has longer to dissipate with the longer off time...

-Brian
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Old Jan 24, 2013, 12:02 PM
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Old Jan 24, 2013, 12:07 PM
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Originally Posted by Retiredtech View Post
Read the FAQ here, especially #3:
http://www.castlecreations.com/suppo...enix.html#phx3
quote: "It is important to note that each on phase of the pulse is equal to the full current draw of the motor and prop at full throttle. Thus, the importance of all components in the system be fully capable of extended periods at full throttle." end quote

This is Castle's ESC ratings:
Max continuous amperage at full throttle = 90 amps (rating determined with 5mph airflow across the ESC)

On a PWM (switched) ESC (not necessarily all 'brushless ESCs as stated previously ... some are now switched) the only way to get a true AMP draw is at full throttle because almost all 'hobby quality' ammeters measure the average current of the pulses, not the peak current. Another spec to check is the BEC rating of the ESC.

RT
There are non switched brushless ESCs? how do they work? You've piqued my interest. I'd figured they have to be in order for the motor to get the 3 phase required.

-Brian
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Old Jan 24, 2013, 12:11 PM
I just want to go fly!
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thanks. ill get a test going when my meter arrives. plenty of time with this weather. when i install a larger 54 amp esc should i also install a external bec for safety or is it not needed with the larger esc?
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Old Jan 24, 2013, 12:30 PM
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Old Jan 24, 2013, 12:37 PM
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Quote:
Originally Posted by Retiredtech View Post
Read the FAQ here, especially #3:
http://www.castlecreations.com/suppo...enix.html#phx3
quote: "It is important to note that each on phase of the pulse is equal to the full current draw of the motor and prop at full throttle. Thus, the importance of all components in the system be fully capable of extended periods at full throttle." end quote

This is Castle's ESC ratings:
Max continuous amperage at full throttle = 90 amps (rating determined with 5mph airflow across the ESC)

On a PWM (switched) ESC (not necessarily all 'brushless ESCs as stated previously ... some are not switched) the only way to get a true AMP draw is at full throttle because almost all 'hobby quality' ammeters measure the average current of the pulses, not the peak current. Another spec to check is the BEC rating of the ESC.

RT
But when they state 90 amps continuous, they're talking about average, not peak pulse current. Just some guesstimation, but I would think this means that the pulse rating is going to be 135A. [2 phases active at once, so the components see only 2/3 duty cycle, even at WOT it's switching the phases. So to average 90A means the pulses would be 1/3 more to account for the 30% off time. 90=(135+135+0)/3]

Well, while writing this I found:
http://www.rcgroups.com/forums/showp...1&postcount=58

So it seems that I'm not far off on my numbers here, or theory here. In that example he's drawing 0.95A off the battery while the ESC is providing 3.6A pulses to the motor @ 75% throttle. At full throttle, he was drawing 1.3A and peaking at 2.4A (I would say each pulse averages a little under 2, though) So by the above math: 2.0 + 2.0 + 0 / 3 = 1.33A

I gotta say, that's a dang interesting thread!
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Old Jan 24, 2013, 12:46 PM
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Old Jan 24, 2013, 01:04 PM
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Originally Posted by Retiredtech View Post
Wrong. When the ESC is operated at 'full throttle', the pulses are essentially a straight line. Read the FAQ # 3; it states: quote: "It is important to note that each on phase of the pulse is equal to the full current draw of the motor and prop at full throttle. Thus, the importance of all components in the system be fully capable of extended periods at full throttle." end quote. That means that each pulse is at the 'full throttle current'.

You need to find a book on switched ESCs to learn how they operate.

RT
A pulse cant be a straight line, its not a pulse.

If you had straight line input to all 3 phases the motor would stop.........or am I missing something here

Dave
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