How to test an electric motor. - RC Groups
Apr 04, 2010, 02:50 AM
Registered User
Discussion

# How to test an electric motor.

Testing an Electric Motor.

When buying an electric motor, the first thing we do is try.
So check their performance, the engine is the one that bought and is in good condition.

To test covers the following:

ESC. Make sure it is of a rating above that are responsible.
Battery. In the appropriate cells and the necessary capacity.
Ammeter. Is connected in series to the battery to measure Amps. If you have better multimeter.
Support. For the motor.
Propellers
Battery Lamp
Tachometer.

First, assemble the engine, we put the connectors, the mounting of X and bolted to a foundation. (As I use a vise to hold the engine mounts to a piece of wood 3/4x2x6pulgadas.)

The base engine with the look of a vise, which is firmly bolted to a desk.

The engine if silver or gold bell, we put 2 black marks on opposite sides. Marker. And if we put 2 black white or yellow labels.
This is done so that we can measure the RPM when it has no propeller.

Turn on the radio, you connect the battery, and we hope to be armed.
I accelerate slowly, bumping the consumption of amperes, which must be very low because the engine has no load.
With a tachometer and pointing the lamp measure the RPM. (Light and tachometer have an angle as 30 degrees. View video)
Amper reading aim, if possible voltage and RPM.
If we read voltage, then we can calculate the KV.
Kv = rpm no load / volt.

The formula is more complicated, but the result is only slightly different. So it is not necessary to use it.

We hope that the manufacturer's specification and the measure obtained from KV are approximate.

Now we prove different propellers and with the same battery. Preferably, with propellers more small than recommended, to give us an idea of how I may have specified.
And reading tests are rapid, 10 to 15 seconds and checked the temperature of the engine.
If the engine burns when touched, then the propeller is very large. (See video)

A test can make is to put the engine about 30 sec. And if you can touch, then the engine is fine with that helix.
You have to consider when making this test, the amps are measured below the manufacturer recommends. (See Video)

As a rule, I try not to put a propeller that gives me less than 70% of the KV. or Ratio.
So a 1000kv motor. A 11 volts I put a helix of at least 7700rpm.
If given less I have to be more cautious, testing only for a few seconds, less than 10 and then let the engine cool.

All data engine gives me the points in a leaf and labeled with the name of the engine.
Feed data into the program Drive calc. And so I say as an official program with all the other propellerts and the limits to different voltages as well the main thing I check the efficiency.

En Espanol.

Manuel V.

### Images

Last edited by manuel v; Apr 04, 2010 at 03:01 AM.
Apr 04, 2010, 02:55 AM
Registered User
 Probando un Motor. No load. (0 min 43 sec)

 Probando un motor. Con helices. (3 min 10 sec)

 Probando un motor. 40 segundos. (1 min 37 sec)

Manuel V
 Apr 04, 2010, 07:53 AM An itch?. Scratch build. I usually just put it in a plane and go flying. But I'm sure what you have done will help someone.
 Apr 04, 2010, 07:58 AM Registered User Come on, Ray... you might not do the testing yourself, but I'll bet you check out the weight and the specs and any performance data you can get your hands on before fitting a Motor X into Plane Y. I can't see you fitting a heavy low Kv motor into a parkjet or a tiny high Kv motor into a draggy plane.
 Apr 04, 2010, 11:19 AM Suspended Account Hi Manuel, I think your post will be very helpful to many people who want to learn the steps and methods to pick the right motors for their planes. Thanks for taking the time to do this! Chuck
Apr 04, 2010, 02:14 PM
An itch?. Scratch build.
Quote:
 Originally Posted by Dr Kiwi Come on, Ray... you might not do the testing yourself, but I'll bet you check out the weight and the specs and any performance data you can get your hands on before fitting a Motor X into Plane Y. I can't see you fitting a heavy low Kv motor into a parkjet or a tiny high Kv motor into a draggy plane.
Agreed, but I would select/buy a motor that I was confident in to do the job in the first place.

If I had to test it after buying it to see if it was suitable, well then the above may come in useful.

There is enough information within the forums and threads to give a high probability that you will find the motor you need for just about any model, (most has probably been supplied by yourself, and much appreciated. Thank you.).
And yes, I have bought some motors in the past that haven't lived up to my expectations when airborne, but a bit late then.

As is often pointed out about thrust rigs, it doesn't neccessarily mean the plane will fly exactly how you want because you have all the static thrust information.

But if it all helps others to enjoy the hobby, no problem.

You have to remember I'm an 'Oldie', that mean I tend to disagree with everyone, myself included.
Apr 04, 2010, 02:20 PM
An itch?. Scratch build.
Quote:
 Originally Posted by Dr Kiwi Come on, Ray... ..................... I can't see you fitting a heavy low Kv motor into a parkjet or a tiny high Kv motor into a draggy plane.
Actually Doc, I have just done that, I replaced a lot of lead and a lightweight motor in my Avro 504k biplane, with a heavy low kv motor, needed to get the CG correct, and propped the motor to suit the models flying style.

We live and learn.
 Apr 04, 2010, 03:03 PM Registered User I understand, but an Avro 504K surely is no "parkjet".
 Apr 04, 2010, 06:59 PM Registered User This is good Thanks
Apr 04, 2010, 09:32 PM
Registered User
Here is my test set-up:

### Images

 Aug 15, 2010, 01:34 PM Registered User Manuel you gave me exactly what I was looking for, te doy gracias
Aug 16, 2010, 12:09 AM
Registered User
Quote:
 Originally Posted by oneofsharp Manuel you gave me exactly what I was looking for, te doy gracias
You are welcome.

eres casi mi vecino.
Donde vives, En Tucson.

Manuel V.
Aug 16, 2010, 01:00 AM
Registered Drug Free
Yes I always test the no load rpm first, and then run up a few of the props I intend to fly with, just to make sure there are no nasty surprises.

I just modded my IC engine break-in bench aka saw horse, to accommodate my electric motors, just a couple of plates welded together to fit a common aluminium motor box which is held to the horse by a standard tatone engine stand.

Mike.

### Images

Aug 16, 2010, 06:35 AM
Way to many airplanes!
Quote:
 Originally Posted by Dr Kiwi Here is my test set-up:

Doc,

Is the extra weight on the scale for better accuracy?

How do you use the flashlight?... Looks like some sort of opto device for the RPM but not obvious....

I like your setup and will try to do one like it. I also like to test my motors first, and sure enough, I kind of like buying mine from place like Hobby King. So mesuring trust is kind of must. Not that they sometime push their numbers a little....
Aug 16, 2010, 07:18 PM
Registered User
Quote:
 Originally Posted by LunaRendezvous Yes I always test the no load rpm first, and then run up a few of the props I intend to fly with, just to make sure there are no nasty surprises. I just modded my IC engine break-in bench aka saw horse, to accommodate my electric motors, just a couple of plates welded together to fit a common aluminium motor box which is held to the horse by a standard tatone engine stand. Mike.

Nice motor stand.

Manuel V.