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Old 05-24-2011, 06:27 PM   #1
leea
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Default Can I determine wattage of unknown motor

I have a motor I bought years ago that has no markings and I don't know what it is designed for. I attached a picture of the logo but it may be upside down or sideways. It does have 014 on it. It has 6 poles and is a brushed motor. Is there a way to figure out how much wattage I can pump into it? I put a 7/6 prop on it and connected it to a 3 cell Lipo for a short time and my 10 amp meter was out of range so I assume maybe more than 100 watts. I thought if I ran it for 5 minutes and it didn't get too hot would that be a way to tell? If so test with or without a prop? It is fairly sealed and there is no way to measure the temperature of the windings and therefore air cooling is minimal. If I run it on the 3 cell lipo and it burns up I won't care too much.


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Old 05-24-2011, 06:33 PM   #2
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First, don't ever bench run motors for 5 minutes static - it is a good way to burn them up.

Static testing = <30 seconds. They just don't cool well and they are stalled statically. This testing is important and gives you a good idea to start air testing, but is just that a check for worst conditions (stalled prop on the ground). This is the test to know you are not going to burn anything up in the air since you are below capacity for your motor/esc/battery.

I generally static test for 10-15 seconds - especially on larger power systems.

Some questions:

First what type of motor is it? Brushed, brushless etc...

Second a full pic of the motor would help.

As a general rule a decent brushless motors are good for about 3 watt per 1 gram. So a 33g motor is generally about 100w max. A 1000g motor good for 3k watts etc.

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Old 05-24-2011, 07:01 PM   #3
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Boy, you guys are fast. Right after I posted I edited it to add it is brushed. It is a plain generic motor about 28 mm in diameter and the body is about 35 mm long. I weighted it with prop and mount so guessing it is 60-70 grams.


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Old 05-24-2011, 07:24 PM   #4
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Given how dirt cheap you can pick up small brushless motors these days is it really worth spending lots of time end effort with this motor?
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Old 05-24-2011, 07:31 PM   #5
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It is s400 size but a bit shorter than a normal can. I suspect you are looking at about 70w maybe 80w motor. Don't know what the kV is but I would start with a very small prop.

What is your intended application for this? And like posted above with brushless motors there are MUCH better choices these days.

Mike
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Old 05-24-2011, 09:24 PM   #6
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Generally these motors were designed for operation with 6 or 7 NiMh (7.2 or 8.4V) cells and even then the brushes (and the bearings) have a finite life, measured in a few hours. They had cooling slots in the front and back of the casing. Without cooling they were meant for low power applications only.
On a 3S LiPo (11.1V) even if the total power is kept in check, the brush life will be that much shorter, mine lasted less than an hour.

A brushless out runner of the same power is about half the weight, runs on sealed ball bearings and is electrically about 20% more efficient. In normal use its life is almost unlimited.
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Old 05-25-2011, 02:28 AM   #7
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Originally Posted by leea View Post
Boy, you guys are fast. Right after I posted I edited it to add it is brushed. It is a plain generic motor about 28 mm in diameter and the body is about 35 mm long. I weighted it with prop and mount so guessing it is 60-70 grams.
With the price of the smaller brushless motors and their corresponding ESC's (Electronic Speed Controls) working with a brush type motor will work. But you'll get double the performance, with less weight, and longer flying time on a given battery for the system.

(I went through brush type motors back in the 1980's, up through geared brushless motors, to the present brushless outrunner motors that we presently use. These brushless three phase motors can run 100 watts per ounce of motor weight, so a good, high quality 8 ounce motor can put out about 800 watts, or one horsepower.)

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Old 05-25-2011, 04:05 AM   #8
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I know and agree that a new brushless would be the way to go. However I am unemployed over a year and building this with the junk I have on hand. I have to be careful were I spend. I was hoping for a bit of cheap fun and hoped I could do something with this. I was hoping for more than an hour though but if that is all I get so be it. I will probably crash it before then :-)
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Old 05-25-2011, 04:20 PM   #9
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I am concerned at the lack of cooling slots in the motor.
It really should have something like this.
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If your doesn't then it not intended as a 'flight' motor and will probably not be able to produce the power you need to fly.
If you already have a brushed ESC (electronic speed control) you could give it a try, if not then you really would do best to buy a brushless motor and ESC.

If you could let us know what size and weight of plane you have in mind I am sure you will be advised what motor, ESC and prop would be suitable. It can be done quite cheaply.


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Old 05-25-2011, 09:33 PM   #10
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Originally Posted by quorneng View Post
I am concerned at the lack of cooling slots in the motor.
It really should have something like this.
Attachment 148629
If your doesn't then it not intended as a 'flight' motor and will probably not be able to produce the power you need to fly.
If you already have a brushed ESC (electronic speed control) you could give it a try, if not then you really would do best to buy a brushless motor and ESC.

If you could let us know what size and weight of plane you have in mind I am sure you will be advised what motor, ESC and prop would be suitable. It can be done quite cheaply.
Some of those "back yard fliers" can be powered by a geared brush type motor that will set you back perhaps $10 - $15 depending where you shop.

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