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Matching ESC to Motor?

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Old 03-20-2011, 06:41 PM
  #1
kingtoyota
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Default Matching ESC to Motor?

Hi All. New guy here, so go easy on me!
My son and Iare getting into electric planes, and we were wondering how to match up an ESC to a motor?Iknow about the amps, you need a bigger ESC amp-wise than you will draw from your motor. Iread about different motors- 10 turn, 12 turn? Is this the windings inside? Idon't remember seeing those specs on motors or ESC's.My son has made several foam planes which worked out good with a combo kit he got online. He has several 3 cell lipo batteries. He tried a 30A Suppo ESC, and a 2212-06 2200KV Suppo motor. The motor studdered under load and the ESC fried a chip inside. Please help!

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Old 03-20-2011, 07:32 PM
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Default RE: Matching ESC to Motor?

G'day

Like you I am struggling with electric motors and the associated bits but I have learned a bit so here is what I do.

Take a typical example motor. If you go to hobbyking.com and then go to Brushless motors and then the Turnigy SK series motors you will see that the 5th motor down (when I looked) was a TGY Aerodrive Xp 32 SK series 35-48 900kV/770 W

So what do these numbers tell us. The most important is the 770 W or 770 Watt. This tells us it can dissapate 770 Watts before it blows up. With a 3 cell battery (11.1 Volts) assume a voltage to the motor of about 10 Volts (which is about right) so at full power this motor needs 10 Volts x 77 Amperes to generate 770 Watts. If I were using this motor, I would put a prop on it and a 3 cell battery and measure the current draw and use the biggest prop that would cause the motor to draw about 70 Amperes. Then I would use an 80 Ampere speed controller.

The motor can deliver 900Kv, that is for every Volt it will give about 900 revs so at 10 volts we will get about 9000 revs ( so long as we don't over prop the engine).

This particular motor is quite large. It is 35mm in diameter and has magnets 48mm long.

The best thing I have bought recently is the Tunrnigy Watt meter. If you look under Tools, Measuring on page 3 you will find it for $23.95. You need to fit it with connectors to suit your particular battery connectors. This will tell you just how many Amperes your motor/prop combination is drawing. If it is too much for the ESC, you can go to a smaller prop or get a larger ESC.

ESCs don't last for ever. I had one blow up recently. The quality from China is OK but not great but it does seem to be improving. It certainly is cheap. Look at the price of Graupner or Robbe ESCs to see what quality (expensive) ones cost.

Hope this helps a bit. Ask some more questions and I will try to answer them. We have not even touched batteries here.

Mike in Oz

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Old 03-20-2011, 08:01 PM
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Default RE: Matching ESC to Motor?

The biggest thing is not to over AMP the motor. Check the motor amp rating first. There is two of them, constant and burst. Burst is for 10-15 sec, thats it.

2nd put a ESC in the plane that will handle the max amp load for the motor. So if you have a motor that will do 40 amps with a burst of 45, you want a 50A ESC min.

3rd, find what amp load your prop is going to put on the motor. You can over amp ANY motor with a prop that is too big.

4th, get a Watt Meter, there cheap. This will let you know what amp load your getting out of a prop with a full battery. If your motor is good for 30A and you put a prop on the plane that pulls 45A, stop and remove the prop. You only have to run a motor for a couple of sec to get a amp reading for the Watt Meter.

Look up "Scorpion Motor Calculator". Down load it and use it to get a ball park estimate of what amps a prop with pull.
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Old 03-21-2011, 06:21 AM
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Default RE: Matching ESC to Motor?

The amount of current that any particular electric motor might draw will vary significantly depending upon the size of propeller that the motor is turning. Some folks will use a wattmeter to actually measure the current draw of a particular motor and propeller before choosing an electronic speed controller.

Other folks will simply order a recommended ESC based on the recommendations and/or specifications for the motor that they choose. If they don't use too large of a propeller, it usually works out OK.
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Old 03-21-2011, 08:21 AM
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Default RE: Matching ESC to Motor?

Thanks for taking time to reply. We have a lot to learn!

So from what Iam reading you can use any ESC as long as the Amperage is not too high for what the ESC can handle? And you an use as big of a prop as you want, as long as you do not draw too many amps? Ihave seen some motors will recommend a certain size prop, but the plane kit says use a bigger prop than that. Will that work as long as the ESC can handle it?


Iwill definitly get a watt meter to check things out. The one on HobbyKing is backordered, so I will have to look around.

Thanks again for the help!

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Old 03-22-2011, 03:39 AM
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Default RE: Matching ESC to Motor?

Safest thing is to go by the recomended amp rating of the motor. Using the wattmeter, pick a prop that draws as close to the amp rating of the motor. This gives you the most out of the motor. If you from a 3 cell to a 4 cell batt you need to use the wattmeter again as the same prop will draw many more anps with the higher voltage. Use the wattmeter to get the amps down to the original recomendation. Also if you go to a 2 cell batt, it can handle a bigger prop. Amp rating of the ESC should be about 20% more than the motor amps. A higher amp rating will not hurt anything other than the extra weight. The stuttering of the motor can be caused by to big of a prop and/ or wrong timing. Good ESCs that I use are the Turnigy Plush from HK work well and can be simply programmed for timing etc, with their programming card. Hope this helps.

Gord.
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Old 03-24-2011, 01:20 PM
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Default RE: Matching ESC to Motor?

Hi y'all,

Though the thread pretty much seems to have ended over here, but I have a question. I've never flown any electric plane. I've been given a Kit of Sig Kadet II by a friend of mine for free and it's 40 size. In couple of weeks I'm gonna start putting it together and it's gonna be my first Kit ever built under a senior guy's supervision. I want it to be electric. So what are my options

1. What motor do I need for it, I want Brushless motor and good price
2. Which ESC
3. Which Battery Pack
4. What servos
5. What size prop.

I'd appreciate the reply to it and the clarification, so my mind does not get boggled down. Also how much all these items would cost? would it be over $100?

Thanks

Mody


***Didn't mean to hijack the thread.
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Old 03-24-2011, 01:32 PM
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Default RE: Matching ESC to Motor?

Mody, it seems no one bothers to look at what is offered in the header bar. I still know nothing about electrics but when I built my first one I went to the bottome of the bar and went to wattflyer forum. Really a good site, I can't stress that enough. There are posts right there, Everything You Need To Know About Electrics that someone really did a great job with. After that I had some understanding of what was needed and how to figure it out. Then I asked questions in the beginner forum and met some really nice people that really helped me out. My first electric turned out perfect.
Take a little trip over there and see what I'm talking about. Electric is all these folks do so there is a lot of good advice there. I was even pointed to someone that had built the same plane as mine.
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Old 03-24-2011, 01:38 PM
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Default RE: Matching ESC to Motor?

Thanks Gray,

I'm gonna do that. I did not wanna start any new thread, just added to it, and I get answers mostly over here by good people. Now I've been given the right direction by nice gray beard

I'd research there.

Thanks again

Mody
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Old 03-24-2011, 01:45 PM
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Default RE: Matching ESC to Motor?

My post was intended for anyone needing help with electrics, not just you. Most answers can be found here but over on wattflyer these people for the most part are into electrics more then us on this site. I was able to get the answers I needed there on everything from motors to batteries and ESCs. You don't even need to ask a question, just read the stickys they have for new people. The people I met there really knew there stuff and could answer this dumbass in terms even I could understand. They didn't even rag on me when they dumbed it down for me.
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Old 03-24-2011, 01:59 PM
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Default RE: Matching ESC to Motor?

Hey Gray Beard hello from windy Michigan. I tried to go to the site that you were referring Armody to but I don't see it. Is it listed as wattflyer? Temp here is up a little but wind gusting 25-35.
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Old 03-24-2011, 02:02 PM
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Default RE: Matching ESC to Motor?

Gray,

I found this thread which is extremely long and looks very very informative., I'm gonna read up on it and take it slow

http://www.wattflyer.com/forums/showthread.php?t=31368

Also my friend who gave me the kits, he flies electrics, ducted fans, so he is also gonna guide me pretty well about it and help me out, so he is also a great advantage, after reading and putting my questions in the forum, it cropped up in my mind that, he is into electrics.

Thanks once again, I rouse the thread
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Old 03-24-2011, 03:34 PM
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Default RE: Matching ESC to Motor?

Consider the watts per pound guideline:

You can determine the power requirements of a model based on the ‘Input Watts Per Pound’ guidelines found below, using the flying weight of the model (with battery):

50-70 watts per pound; Minimum level of power for decent performance, good for lightly loaded slow flyer and park flyer models
70-90 watts per pound; Trainer and slow flying scale models
90-110 watts per pound; Sport aerobatic and fast flying scale models
110-130 watts per pound; Advanced aerobatic and high-speed models
130-150 watts per pound; Lightly loaded 3D models and ducted fans
150-200+ watts per pound; Unlimited performance 3D models


So, if you have a plane that weighs in at 25 ounces. That works out to roughly 1.5 pounds. To fly this at sport aviation levels, it will take 1.5 X 110 watts or 143 watts. If you use a two cell LiPo, that's 7.8 volts (nominal). 7.8 volts works out to a battery capable of supplying at least 18 amps. So, a 2000 mah pack is pretty much minimum for this plane, and you have to consider how you want to fly it at that and that's where the C factor comes in.. how long and how much burst power do you want/need? A three cell Lipo will need less current.. but you get the idea, i'm sure.

It's not as simple as just putting a battery on the plane and trying it out. You chance burning up both the motor and the ESC with the wrong selection.

Remember that when making weight measurements (not estimates, unless you know exactly what each component weighs), everything has to be considered: airframe, motor, esc, battery pack, receiver, servos, everything.

Next, there is a prop load to consider. OpJose posted a very good outline about this. This is a cut and paste from his post:

Snip -

Actually it's quite simple...

To get 1:1 you want around 120-130+ watts per pound maximum ( burst ) power.

So if your plane is going to weight 15.2oz ( as projected by the manufacturer ) then take a figure OVER this and multiply by 130watts...

So let's say the plane will weight 20oz AUW just for safety....

1.25lbs x 130w = 162 w

So a 180 watt motor will do the trick.

Assume that you'll use an 11.1v LiPo pack...

180w / 11.1v = 16.3A

A 20A-25A ESC will work fine

Thust HP says that a 8x6 prop spinning @ 11000 RPM produces about .234 HP

1HP = 745w

.234 * 745w = 174w ( right in the ballpark! )

So we can use an 8x6 prop and spin it at 11000 RPM.

11,000 RPM / 11.1v = 990KV or approximately 1000KV

I'd use an 1100KV motor to add a bit more power.

Finally let's find the battery we'll need... we'll want to drive it only to a maximum of about 15c if it is rated for 20C.

16A will be our maximum draw

16A * 20/15 = 21A @ 20c

So a 1000mAh to 1200mAh 11.1v 3S pack would be the smallest you can use... I'd go with something around 1300mAh+ for safety. 1800mAh would give you the flight times you want but adds weight.

So there you have it.

1300mAh+ 3S 11.1v LiPo
8x6e prop
20-25A ESC with BEC
1100KV Motor rated up to 180-200watts burst for 15-30seconds. ( look for a 150w motor or so ).

Snip

I don't want to oversimply this and insult your intelligence, but, here is the basic math for watts, amps, and volts:

Ohm's law (algebra) :

Volts X Amps = Watts

Watts/Volts = Amps

Watts/amps = Volts

Easier stated, multiply volts x amps you get watts. 11.1 Volts - three cell LiPo multiplied by 20 Amps drawn = 222 Watts

222 Watts divided by 11.1 Volts = 20 Amps

And so on.

http://www.hoppenbrouwer-home.nl/ika...rusthpv20d.htm

I believe this is a German site, but the information is there and you can use the calculator to determine prop size.

The person that said electric flight was easy must have gotten a A in college Calculus... [X(] [&o]

I hope this helps.

CGr.
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Old 03-24-2011, 04:42 PM
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Default RE: Matching ESC to Motor?


Quote:
ORIGINAL: goirish

Hey Gray Beard hello from windy Michigan. I tried to go to the site that you were referring Armody to but I don't see it. Is it listed as wattflyer? Temp here is up a little but wind gusting 25-35.
Gene, very bottom of the header. That 80 degrees we had didn't last all that long. Storms flowing through, winds from 30 to 70 and it has been raining. Light but rain none the less. Back to long pants and wool shirts. We should be back to normal in a week or so. I'm taking the time and running my batteries through the cycle machine. Found one bad one in my CG Extra. I got lucky on that one. Took a charge but would only drop 3 or 400 mah.
Gene
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Old 03-25-2011, 09:51 AM
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Default RE: Matching ESC to Motor?

CG,

Very informative and very detailed.

Thank you

Mody
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Old 03-25-2011, 02:43 PM
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Default RE: Matching ESC to Motor?

Thanks, Mody, but only part of it is from me. I cut and pasted some from other posters, mainly Opjose.

CGr.
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Old 03-25-2011, 03:31 PM
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Default RE: Matching ESC to Motor?

Well I found the site thanks to Gene (the other Gene) Sitting here now with several slices on my forearm from a spinning prop. Engine started backwards and was pushing the plane off the stand. Reach for it and didn't clear the prop.
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Old 03-25-2011, 03:45 PM
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Default RE: Matching ESC to Motor?

Gene, just because it's electric doesn't mean it won't bite!! I saw the photos of one fellow that was setting up his electric on the bed. It was pointed at him and he kicked on the power. He caught it, it was ugly!! These little props are sharper then the props we use on our glow planes. Sort of like catching a slice and dice!!!
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Old 03-25-2011, 04:38 PM
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This wasn't electric. Glow 108. Got me about 6 times before I could move my arm.
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Old 03-26-2011, 03:07 AM
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Default RE: Matching ESC to Motor?

[:@] I did that with an electric. First motor start after installation, didn't think to remove the prop. The throttle was reversed and I didn't know it. So, when I went to full, it was actually idle so when I went to idle, well, 5 stiches later....

CGr.
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Old 03-27-2011, 04:20 PM
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Default RE: Matching ESC to Motor?

Thanks for the link to the wattflyer forum.

http://www.wattflyer.com/forums/showthread.php?t=31368

Ihave been reading this slowly and digesting it. It is exactly the information Iwas looking for.


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Old 05-11-2013, 08:35 AM
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Default RE: Matching ESC to Motor?

When measuring amps drawn on a multi engine project, do you divide the total amps by the number of motors to determine the proper esc size needed? Thank you, for any help.
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Old 05-13-2013, 01:52 PM
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Default RE: Matching ESC to Motor?

Quote:
ORIGINAL: Shoestring1958

When measuring amps drawn on a multi engine project, do you divide the total amps by the number of motors to determine the proper esc size needed? Thank you, for any help.
No. Each Motor requires it's own ESC.

The ESC must be sized to the demands of the PROP (most important) and motor (less important).... after all it is the PROP not the motor that determines the amount of power the motor will attempt to draw.

Treat the ESC choice as if you are only sizing things for a single motor then get two of those ESC's.


However for the batteries...

You MULTIPLY the total current consumed by each motor/ESC combination by the number of motors to determine the AMP draw the batteries will see if you are drawing current from multiple motors off of one battery pack.

If each Motor/ESC combo will draw a momentary maximum of say 20 Amps you'll need a pack capable of at LEAST 40 Amps in a two motor setup and that will be marginal.

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