Here is a copy of an email sent to Castle Creations from Bruce Hoffmann about controller temps and their reply to him.
I thought that this would be good info for us "leckies".

To: Castle Creations.

Hi,

I've been using the Ice 50 ESC for the past year in Competition Control Line Stunt models - originally I was using an 'Arrowind' 2832 motor (960kv 14 pole) with a 13 x 4.5" electric propeller but recently have changed to a "Plettenberg" 2510, 930kv 10 pole motor.  I ran both at set RPM's of between 9000 and 9400 using 4 cell batteries of between 3000 and 3700mah's.

I've had no problems with the systems I've operated but have been wondering 'what' the safe temperature range (in degrees Celcius) would be.  I recently checked the logging data and saw that temps. had gone up to about 68 deg C.  Is this too high or in what you would believe to be a 'normal/safe' range - what would the max. safe temperature be?

Many thanks,

Bruce Hoffmann
Australia

Hi Bruce,
 The max temp for the controller where it will shut down is 100C. Though 68C is not too bad, I would still rather see it at about 55C or less.
Which Gov. mode are you using? I entered the information you gave on the motor/pole count & the speed of 9400 into the vehicle information of the Set RPM Gov mode and when I look at the info tab beside the Desired Speed box the percent of throttle used for 9400 is only 75% (on 4s). This is a very inefficient throttle percentage. The gov. will work very well here but will build a lot of heat. I personally like to see this number above 88 & even better between 90 & 93%. I have attached pics so you can see what I am talking about. To get into that efficiency range you would have to enter something around 11000 rpm into the head speed box but with what ever prop your using may not allow it.
Getting the efficiency  just right in control line takes a mixture of the correct Kv, Prop & speed. Just playing with your set up on the Castle Link if I change the speed to 9000 & drop the voltage to 3s you get 96% on the throttle which will run the motor at almost full speed giving the best efficiency.
Hope I haven't confused you but if you can get that % number between 88 to around 95% you will for certain see temps come down.

Just in case your not familiar with the Set RPM mode it basically works the same as Gov. Hi/Lo except you have 3 available speeds that are selectable by a range of millisecond inputs from what ever you have controlling your throttle. The first Desired head speed box is for in puts up to 50% (this is based on Helicopter throttle curves but the millisecond input will work the same) which is 1.1ms – 1.5ms. The second box is selected with a range of 1.5 – 2.0ms & the 3rd box for anything greater than 2.0ms.

Hope this helps & if I can be of further assistance please let me know.


Thank You,
Steve Rogers
Castle Creations
Outside Sales & Support
540 N. Rogers Rd.
Olathe, KS  66062
www.castlecreations.com
Direct - 913-948-7582
Cell – 828-246-2170

that is quite interesting -but what effect does it have on the motor heat running it at +/- 90%  throttle?

That depends on how fast they're switching the voltage to the motor, but in general it'll reduce the motor losses somewhat.  How much depends on a lot of details that are up to them and the motor manufacturer, and I don't have any fancy ESC's to put on my O-scope.  It probably has a lot more effect on the ESC heat than the motor heat.

How is the motor more efficient at higher RPM?  seems conflicting

I think he's saying that if the motor speed is closer to max RPM then the system efficiency will be greater.

Someone needs to educate Castle on the peculiar needs of motor control for control line precision aerobatics.

Eeeuuuw!!!.......My head hurts!!   

Wow, Igor,

You lost me and at least half of the electric C/L fliers that frequent this forum. 

I'll read it again a time or two and maybe it will sink in. 

Meanwhile I have a Thanksgiving turkey that is calling!! 

Thanks for the excellent explanation Igor. If you ever start teaching electronics in school, I would love to take your class. It would be cool to see all your pictures and charts! 

While watching my football team beat up on Jone's ego, I wish I was smart enough to come up with a football analogy to explain this, but alas, I am not that smart. 

Our modern ESCs are fantastic, magical devices. Think, All pro quarterback Drew Brees + Brilliant engineer Igor Burger in one person! 

Below is how I interpret what Igor said ..... I could be wrong, it has happened before ..... just ask my wife! ;-)


The ESC is in the middle with the motor on one side and the battery on the other.

The ESC tells the battery: give me some energy

The ESC sends a burst of energy to the motor and the motor says: oh, that's were the Electric magnetic field is, I'm going to rotate in that direction to line up my magnets with it.

Just before the motor rotation gets there the ESC sends another burst of energy moving the field a little farther, the motor starts to chase this constantly moving target that the ESC keeps moving at VERY fast speeds.

The ESC is constantly asking the battery for more power to send to the motor, and the motor is trying to ask for just the right amount of power it needs to spin it's prop under varying loads at a set RPM.

In our ECL The ESC has a LOT of power coming into it all the time from the battery. "IF" we selected the correct motor, ESC, and battery, Prop etc. for our system then the ESC can just keep sending all this power STRAIGHT through to the motor, with very LITTLE off time during its constant ON and OFF switching to rotate the motor. In this case the ESC does not get too hot.

"IF" we are using a motor that is loafing too much (KV 950 * 14.8V = 14,060 RPM, but we only need 8,500 RPM, 60%) this means that the ESC is sending short ON bursts of power to the motor with (relatively) long OFF times. This means that a LOT of energy is TRAPPED inside the ESC and it has to dissipate much of it inside it's FETs in the form of heat.

This does NOT bother the motor too much, but the ESC does not like it at all, it gets HOT to show us it's displeasure at our poor system selection skills!

Our ESCs are much happier if the motor is telling it "FULL SPEED AHEAD SCOTTY, GIVE US ALL YOU GOT!" Captain Kirk likes it when most of the Beryllium Spheres are being burned up by the motor and not trapped inside the ESC, heating up the whole STARSHIP ENTERPRISE! 

....... maybe Igor is right, we may need some pictures and charts? 

PS: In addition to our modern AC electricity (Thank you Mr. Tesla :-) we have a lot to be thankful for today! 

Regards, 

 

nicely put Rudy - it is simple when it comes down to it huh.

now - understanding the below - with the system I run at the moment - 890KV -14.8V = 13,172 - but I am running at 9200rpm only - would it be better to be running a 3s 11.1 volt pack to get me closer to 93% plus throttle?

890 x 11.1 = 9879RPM

or are the reasons to use a higher Voltage more beneficial in any way?

Hi Wynn,

Thank you for the kind words. Please keep in mind, Igor is the brains, I'm just a lowly interpreter. 

THE SHORT ANSWER:

NO, do not go down to 3S. YES, there are several reasons that we need the higher V. Stay with the 4S

Your setup, as is, will work OK. It will just have an ESC that needs a little more air cooling than a more efficient setup would require.

A better solution than reducing V is to just get a motor with a lower KV. The motor, the ESC, and the Battery will all be a little happier.   

LONGER ANSWER:

I think we have to be very careful here. Like many parts of our system, the ESC has it's preferences but we should never let the "tail wag the dog". This narrow topics discussion is really one of making sure that we make changes as needed to keep the ESC within it's safe MAX temp limits of < 55C (<130f).

As Steve from CC pointed out, one way is to make sure we select a motor with the correct KV so that FULL THROTLE is above 75% of max, 90% being close to ideal "FOR THE ESC". This high TH setting is NOT NEEDED FOR THE ENTIRE SYSTEM. We can work well with lower % #s if other factors warrant it, (motor size availability etc.)

Now we need to also keep in mind that the ACTUAL REAL #s are difficult to find without some research and "real life" on board testing/measuring. Our leader, Dean Pappas, has wisely pointed out in past posts that there are several factors that reduce the simple KV * V = RPM formula #s.

1. Our V under load may really be closer to 14.4. And if you are using very low mAh batteries, this V # may even be lower toward the end of the flight.

2. The KV may assume a perfect environment for the motor and the real MAX PRM attainable may be less than published.

3. Other inefficiencies are often at work; heat, resistance increases due to heat, etc., etc.

Dean suggested that we use a rule of thumb of multiplying our MAX RPM # by .8 (80%) to get a "TARGET" RPM for our system. Then use a motor KV that gets us near this #. This .8 # accounts for 10% inefficiency's, and the 10% that Steve suggests (90% of max RPM) that we run below MAX RPM. I have always used a 75% as a target RPM, but I think you get the point that we must correct for real life inefficiencies. Since Dean is smarter than I am, I may start using 80% as my target RPM. 

Again, please keep in mind that these are #s trying to reach an ideal. Our modern ECL systems are VERY tolerant of a wide range of different components and still producing more power than we need!

If those new to ECL or thinking about it just use the same components used by people like Paul Walker, and others shown on the "Sticky list" at the top of this forum, they will have no problems. And more importantly, they can just go fly and enjoy the many benefits of ECL without having to know ANY of the stuff we write on these posts! 

Regards, 

thanks Rudy - I am always looking for better ways to do things - but seems that the way I have it set up at the moment is the right way for our application.

I guess that is what happens when you get the right advice from the start!!! 

good topic though - I really enjoy reading this stuff.

Ok, here is my super simple aproach to looking at this and what we need, based upon my actual real in hand electric powered airplanes,, Not math
Keep in mind, as the stored energy in the battery depletes during the flight, the voltage falls off as well. with good batteries ( most of the time expensive batteries) the voltage available stays flat until very close to the point we stop pulling power. On less expensive batteries, the voltage drop curve is much faster.
so,,,,

The reason we really need to have substantial headroom is so that at the end of the pattern, when you go into something like the hourglass, you need to have enough voltage and current delivery to still ramp up the torque on the motor to maintain rpm in the climb, If you run to close to the edge,( either to small of batteries, or to high of an rpm for the system) when you get to this point in the pattern, you wont have the drive to fly the airplane the way we want to .
My take, if you run good batteries, you might be able to drive the system closer to the capacity of the battery without problems, with less expensive  batteries, you may want to carry some extra capacity aloft,, and this is a double hit. Cheaper batteries tend to weigh more, then you need a bigger heavier battery besides. Good motivation for buying the best batteries you can justify IMHO

Wait a min. guys, your ALL correct, BUT we are now talking about three different subjects. Now "my head" is going to explode! ....   

On this thread I (we?) am ONLY talking about ESC efficiency and % of true MAX RPM to keep ONLY the ESC happy. This % has NOTHING TO DO with the % we use for batteries, and motors. They are interrelated yes, but they each have their own % #s. By coincidence they may be similar % #s, but arrived at for different reasons and with different input #s.

It does touch on the motor only because if we push toward the 90% that may make the ESC happy and cool running, we may also be pushing the motor and it's bearings harder than is comfortable on a hot day in our constant high power demand ECL environment. I like to keep as many safety margins as possible and am willing to compromise between system components to do this. That is why I use the 75% of possible MAX RPM using raw published #s. ......  (KV * V)* .75 = Target RPM for flight. This keeps the ESC below it's MAX temp of 130f (with good cooling air flow) while giving the motor a comfortable safety margin below it's MAX RPM ratting.

What Mark said is 100% correct RE: our batteries. We need a LOT of headroom to be safe and be able to have MAX power available at those "peak" times during the end of our sequence (pun intended ;-). It is just a coincidence that our target discharge amount is 75% of max battery capacity. This BATTERY 75% # is really just a compromise between limiting battery size and weight (not dragging around more battery than we need for the mission) AND having a reasonable # of cycles and enough head room to deal with those peaks, and not have a premature battery failure. ...... The electric pylon racers in Europe PUSH ALL the limits, they use almost ALL the battery each flight, their batteries and motors last only several flights and then are replaced. I have seen some hotliners land and you could not touch the battery or the motor for a long time after the flight! ..... I don't think we want to run at these levels, therefore the safe, conservative rules of thumb you see here on this forum. :-)

John:

You bring up a very good point about ESC/Motor RPM "headroom". When we say: TARGET RPM, we are talking about the MAX RPM that the ESC will need the motor to produce during the flight. As seen on other threads on this forum, and on our Eagle Tree recordings, the RPM in gov. mode will often be up to 300 to 400 RPM higher during some maneuvers than the level lap/static set RPM adj. at the timer. THIS measured MAX RPM is what we should use as the 75% to 80% TARGET RPM. This is one of the reasons I use my 75% # when selecting a motor KV, this seems to keep both the motor and the ESC happy and safe. :-)  Remember, this 75% # has 10% factored in for possible inefficiencies already and is still 15% from MAX-MAX that the motor will see at MAX demand. I think this is enough overhead and still a reliable compromise. BTW, if you have to error, I suggest erring on the low side, not the high side of 75-80. Just make sure the ESC gets a good shot of cooling air! ;-)

Using a temp. measuring devise on the ESC may prove helpful during the 1st few flights. There are several, the least expensive is the small units that the RC car guys use. It has a sensor cable that wraps around the ESC, or motor, and gives a MAX readout at the end of the flight. Other methods are even cooler. 

I hope this helps clear up any misunderstanding on this?

Again, if there are any "maybe" interested modelers out there still reading this, PLEASE keep in mind that most of this geek talk is a lot of warm air and it is NOT needed info. to fly ECL. Just copy one of the excellent setups at the top of this forum and you will be very successful ECL pilots. You CAN have fun with ECL without getting a headache  , honest!

PS: When I use CAPS I am not shouting, I just feel that it helps to have some important words standout if they are more important than others. I apologize if it comes across as being rude, that is not my intent. 

Regards, 

Looks like an explosion here 

OK, so I did simple schematic picture of a DC motor. It shows what I mean.

The ESC is replaced by a switch and diode. If the switch is on permanently, motor is powered by constant voltage, it rotates and thus makes a Back EMF which is = actual rpm / kv.

The voltage of battery necessary for that rpm is = BEMF + Imot * ( Ribat + Rimot ) ... this is something we know from rule that voltage of battery must be little higher than Kv of motor dictates. That voltage difference is voltage drop on those two resistors Ribat and Rimot … means resistance of battery and resistance of motor. So that rule 80% is not fixed number, it depends on quality of motor and battery (its internal resistance).

And now comes the trick of voltage /current conversion. The BEMF comes from motor RPM, so does not matter what is the voltage of battery, it is constant since we have constant rpm. Therefore, if we use battery of higher voltage, which would push higher current to the motor winding via those two resistors than necessary to deliver constant power, we must periodically switch off and on that switch in ESC for short time … that is PWM.

The motor coil is an inductance, which keeps current leaking also if switch is off. The current goes via ESC diode. 

So if the PWM frequency is high enough, the motor current with high voltage is almost constant and equal to full throttle of that when battery has proper voltage. But the current with high voltage in the motor (and thus in the ESC) is HIGHER compared to current of high voltage battery. That current makes a heat created on internal resistance of ESC FET switch which has also some resistance (not on picture).

(note: this is about DC motor, BLDC motor has more complex switching “H” bridges, and little different diodes inside, which forces that “diode” current back to the battery instead of directly to the motor, but it does change situation only quantitively, it does not change the principle – the diode current stops early after off, but still exists).

That is one part of thermal loses in ESC.

The second part are switching loses. It comes from finite time necessary to open or to close that switch. The transistor has for a while “some” resistance which is not optimally zero (on) and also not infinite (off). Loses are function of power going via ESC. The problem is, that while commutating frequency is ~2kHz, the PWM frequency is at least 8kHz, means throttled ESC has 4 times more switching loses than ESC at full throttle.

All together means that if a producer says the ESC is good for 50A at full throttle then the reality could be much lower in PWM mode or even worse for low throttle.

Hi Bruce

I think your set-up is good-to-go - your temperatures seem safe.A little over a year ago - before the ICE came out, those of use flying the Phoenix were blissfully unaware that we "needed" to do anything different! 

If you do the ducting right, you should be able to get a little thrust out of the controller and motor heat. 

I had a few flights with my model today - much cooler weather however the temps of the ESC appear to be about the same as on the hotter days when the outdoor temperatures were up between 27 & 30 deg c.  I have spoken to Russell Bond and he's looking at putting some ducting on the outside of the fuselage, directing air over the ESC, and also some 'ramping' of the exiting air ducting to help 'pull' the air through the motor/battery compartment.  I'll wait until he tests his model before I start drilling holes in mine!  Anyway, here are a few photos of my model, I will definitely be altering the 'exit' air ducts as advised on an earlier post..
Thanks to all..

Bruce

Hi All,
I'm gonna stick with my Setpoint RPM recommendation of approximately 75% of Kv * Vbattery.
The good folks at Castle simply do not appreciate that we are trading off heat in the ESC for running characteristics: namely fast load transient response.
Eventually we will get some decent science to show them, but in the meanwhile, there is more benefit, heat-wise, to getting the timing advance set correctly because over-advanced timing is good for nothing but making heat.
Regards,
Dean P.

Hi Dean..

I think you have hit the nail on the head...my ESC is - as you say - in a 'dead air pocket'  , I'll be installing a scoop so that external air can be directed straight onto it and also do some more work on the exhausting air flow.  Will let everyone know what sort of results I get.  There is another competition next Sunday so I should have the 'renovated' system installed by then except right now its pouring rain - and its expected to do so for the remainder of the week!  Hopefully I'll get a chance to try it out before the comp. day!  (at least I won't need to worry about getting a 'needle' setting like the IC guys do!)

Bruce