[JCALF]

I took out my quadcopter for the first time this Saturday. It was a pretty unsuccessful outing, as I crashed my quad on my very first flight, luckily it wasn't very high up or going that fast so there was really no damage to the frame or components. I went for round two: picked up my quad and was tyring to arm it again but it took a couple of tries before it armed. But something went wrong, the left- front motor started smoking! I immediately powered down and uplugged the battery. I looked handled the motor and noticed that the nut holding the propeller in place was loose, so the motor wasn't able to spin the propeller. My question is: can having a loose propeller cause the motor to burn up?

The frame I'm using is an HDFPV that I bought form hoverthings.com several years ago(I don't think they sell this frame anymore), so I've been buying motors from readytoflyquads.com because they seem to make these motors specially made for frames from hoverthings. I was wondering if I could fit other motors onto my frame? How do you know if they're able to be mounted on your frame?

Thanks,

[Mateusz]

Usually motors have markings which indicate motor size that also gives a clue about screws location. But you should always be able to find everything about motor including mounting holes in datasheet, if there is not datasheet, then really bad manufacturer. Most ESCs have overcurrent protection which cuts off the power when current is very high, as in the case of stalled propeller.  I believe your build is from not well matched props/motors/esc/battery and you probably exceed your motor power ratings, since it is not very common to burn motor just with high throttle, but of course can happen.

[JCALF]

Thanks for the info. Here are the components I'm using:
Motor:
http://www.readytoflyquads.com/brushless-outrunner-hacker-style-20-28m

ESC:
http://www.readytoflyquads.com/f-30a-fire-red-normal-esc-with-rapidesc-fw-for-multirotor

The battery is a 4 cell 25-50C Turnigy battery.
I'm not really sure what the propellers are, I think they're 8 inch props.

[TheOtherCliff]

Sorry when you take the props off, the electrical current drops. 

Loose prop nut will not cause burned motor.  You can run these brushless motors without props and they are just fine.  You can always "underprop" but you get overheating and problems if you "overprop".

Generally what happens is that a crash disconnects or breaks a wire.  The motor can't run with only 2 of 3 wires attached.  On next flight, if you give lots of power to try to start it, it will burn up.  If you only give a small amount of throttle and notice that a motor is not starting, you probably won't burn it up.

So at this point, you need to make sure the ESC is not damaged, or you may burn another motor when you hook it up.  I suggest a current limited power supply when you first run it again, or replace both the motor and ESC.  Simply inserting any large automotive light bulb in series with the battery will limit the current.