Electric motor size.

[Stephen farrar]

Hi, I have several electric motors which have nothing on them to tell what size they are. Is there anyway of finding what they are?

[kc]

No

[Dickw]

Do the motors have two wires or three - 2 wires equals brushed, and 3 wires equals brushless.

For a brushless motor (3 wires) you can get a rough idea of the power handling capability if you weigh them and apply the "3 watts per gram" rule of thumb - crude but will give a reasonable result.

Spin them up with an electric drill and measure both rpm and the volts output by the motor and you can work out the kv.

Dick

[Geoff S]

Are they brushless or brushed can motors?

Brushed can motors come generally (though not exclusively) in 2 sizes 400 and 600. You can power them directly from a battery and measure the rpm off load to get an idea of the kv (rpm/volt). Try loading with a prop whilst monitoring the the current keeping it below (say) 30 amps for a 600 size or 10 for a 400 but monitor the temperature too.

You can undertake a similar exercise with brushless motors but you'll need an esc (the higher the current rating the better then you're unlikely to do any damage). You could weigh the motor and estimate its maximum input power rating using the rule of thumb 3 watts per gram. Then load the motor accordingly but carefully using a wattmeter to monitor the current.

So you can experiment and get a reasonable idea of the motor's potential though it is time consuming. However, time is what a lot of us have right now.

Geoff

[Piers Bowlan]

Stephen, a photo says a thousand words, even it it won't tell us their Kv, it is a start. Then tell us the diameter, length, and shaft size. From that someone may say, 'Hey, I have one of those, it's a ... ' They will require testing using a wattmeter to find out what they will do.

[Stephen farrar]

Hi, thanks for the advice. I will have a go at doing what is suggested. Thanks again.

Steve.