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First time electric gone wrong!

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Oldbaldfella21/07/2013 10:10:29
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198 forum posts
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Hi,

recently took the plunge with my first effort at putting my first electric powertrain together. Unfortunately all I ended up with was a smoking engine!

I bought the Phoenix 2000 electric glider airframe from HK, a 1450kv brushless outrunner to power it, a 25-30a esc and a 1500mah 11.1v lipo. On the end of it is a 10" folding prop as supplied.

Giving it a trial blast in the garden, not many seconds of full power resulted in a smoking engine. I do not believe they are meant to do that!

Where did I go wrong, please?

Phil Green21/07/2013 10:31:46
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1552 forum posts
315 photos

I think your motor is far too high a kv for a large folding motor-glider prop, but the first mistake was not using a watt-meter to check the current drawn. With that prop the motor would have been working very hard indeed.

A wattmeter is pretty much essential when setting up a new power train.

Cheers

Phil

Oldbaldfella21/07/2013 10:59:01
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198 forum posts
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Thanks Phil.

If I remember right, smaller kv for a bigger prop? What kv would you recommend for that size prop?

Cheers.

WolstonFlyer21/07/2013 11:38:32
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2104 forum posts
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I would suggest something around 1000Kv for the Phoenix 2000 with the supplied prop.

Such as this:
**Link**
Oldbaldfella21/07/2013 14:19:08
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198 forum posts
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Many thanks

Frank Skilbeck21/07/2013 23:57:35
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I've also posted this link before, it's a free (yes free) motor/prop/battery calculator, if it doesn't have you exact motor in the database then just pick one with the same Kv you can then get an idea of the motor rpm and amps it will draw. I have found the results to be pretty close to actual readings on my combos.

But a 1450kv motor on a 3s lipo will be trying to turn prop at over 14,000 rpm, would be like having a pylon racing 40 in the nose of you electric glider.

Oldbaldfella22/07/2013 07:50:39
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thumbs upPosted by Frank Skilbeck on 21/07/2013 23:57:35:

I've also posted this link before, it's a free (yes free) motor/prop/battery calculator, if it doesn't have you exact motor in the database then just pick one with the same Kv you can then get an idea of the motor rpm and amps it will draw. I have found the results to be pretty close to actual readings on my combos.

But a 1450kv motor on a 3s lipo will be trying to turn prop at over 14,000 rpm, would be like having a pylon racing 40 in the nose of you electric glider.

Allan Bennett22/07/2013 08:44:11
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44 photos
Posted by Oldbaldfella on 21/07/2013 10:10:29:

... I bought the Phoenix 2000 electric glider airframe from HK, a 1450kv brushless outrunner to power it, a 25-30a esc and a 1500mah 11.1v lipo. On the end of it is a 10" folding prop as supplied. ...

You've got good advice so far, but you also need to be aware of the volt and amp rating of your motor. There's quite a few 1450kv motors around, and there may be some that can handle your 10" (10" by what?) prop on 3S supply. though lower kv would be better, as has been mentioned.

For any given motor, battery voltage and prop size (diameter and pitch) are the factors which determine how many amps the motor will draw. Usually you can get a good idea of the right prop either from the motor manufacturer's page (if they quote a range of sizes, and a range of volts, the largest prop will correspond to the lowest voltage), from calculators, or from other users. But you should always check your actual setup with a wattmeter, for manufacturing tolerances in motors and props can make a difference.

Oldbaldfella22/07/2013 13:37:23
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198 forum posts
56 photos
Posted by Allan Bennett on 22/07/2013 08:44:11:
Posted by Oldbaldfella on 21/07/2013 10:10:29:

... I bought the Phoenix 2000 electric glider airframe from HK, a 1450kv brushless outrunner to power it, a 25-30a esc and a 1500mah 11.1v lipo. On the end of it is a 10" folding prop as supplied. ...

Thanks Allan.

Can I go back to ic, please?

You've got good advice so far, but you also need to be aware of the volt and amp rating of your motor. There's quite a few 1450kv motors around, and there may be some that can handle your 10" (10" by what?) prop on 3S supply. though lower kv would be better, as has been mentioned.

For any given motor, battery voltage and prop size (diameter and pitch) are the factors which determine how many amps the motor will draw. Usually you can get a good idea of the right prop either from the motor manufacturer's page (if they quote a range of sizes, and a range of volts, the largest prop will correspond to the lowest voltage), from calculators, or from other users. But you should always check your actual setup with a wattmeter, for manufacturing tolerances in motors and props can make a difference.

Allan Bennett22/07/2013 20:07:10
1603 forum posts
44 photos

Yes, i.c. is much simpler in some respects. But after spending a couple of Sundays instructing a beginner with his glow-powered Arising Star, I remembered why I went electric wink -- no holes in the fuel lines, no disconnected clunk, no hydraulic lock in the engine, no duff glow plug, and no fuel all over my clothes and model!

Here's a very simple calculator that I use to get my motor and prop size **LINK** for a new model; click on Software and then on Web-O-Calc. With that, and a wattmeter to check the actual amps, I've never had a failure with any of my dozen-or-so e-conversions yet.

Erfolg23/07/2013 19:44:48
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11654 forum posts
1297 photos

As Phil Green as written, a watt meter is essential, a must have with electric flight. You are not the first one follicley challenged one (I am sure I beat you) to be caught out in the way you describe.

I have no issues with calculators, as they are useful in confirming your own judgement or guess. Yet neither they or the data sheet, if available, can be solely relied upon. The watt meter tells you what is happening.

You are a lucky guy, if you were unlucky, the motor shorting out, or the ESC frying would probably wipe out your model and equipment, if occurring in the air.

I am not trying to frighten you or make it out to be difficult to fly electric, because in essence it is not. It just needs a little care, in setting up.

Oldbaldfella23/07/2013 20:47:09
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198 forum posts
56 photos

Thanks for all that.

I have just installed a 1050kv and a mate at the club has a watt meter which we can try so........

I have to say, the lower kv motor seems to be pulling much stronger. Weird! wink 2

Much obliged.

Swissflyer23/07/2013 22:19:54
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162 forum posts
41 photos

Quote of Frank Silbeck

I've also posted this link before, it's a free (yes free) motor/prop/battery calculator, if it doesn't have you exact motor in the database then just pick one with the same Kv you can then get an idea of the motor rpm and amps it will draw. I have found the results to be pretty close to actual readings on my combos.

Quote of Allan Bennet

Here's a very simple calculator that I use to get my motor and prop size **LINK** for a new model; click on Software and then on Web-O-Calc. With that, and a wattmeter to check the actual amps, I've never had a failure with any of my dozen-or-so e-conversions yet.

Totally agree with Frank & Allan

These two tools complement each other. DriveCalc will also warn you if you are going to exceed max. safe prop rpm.

One can learn a lot by using DriveCalc to measure one’s own motors and finding that predictions really are within 3% when you do it well. Above all it lets you see that max power claimed by HK etc. are often fictions to be avoided.

WebOCalc is especially useful in setting up the right prop diameter & pitch together with the right kV motor for your model. There is a lot of sophisticated physics built in the model that includes the prop constants for all the props it suggests.

Props are modelled using the Abbot equations which will let you discover a lot of “free” thrust by optimizing prop diameter & pitch speed.

BTW Oldbaldfella, a correctly sized 1’450 kV motor on 3S with a 10x6 folder (more like an 11 inch prop) is going to try and draw 600W so your smoke was well justified.

If you had run it on 2S, it would have drawn 185W & given you about 1kg of thrust at 20-25A & might have survived.

drivecalc221.jpg

So please follow Frank’s suggestion & get familiar with DriveCalc.

I do hope you next flight is less smokeful

BR Mark smiley

Oldbaldfella25/07/2013 07:59:02
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198 forum posts
56 photos

Once again, many thanks all!!!

The 1050kv is now installed and successfully maidened yesterday.

There have been some staggering amounts of thermal lift down here recently which hopefully will continue.

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