jollycub

My Feedback: (5)

I am struggling through the electric motor-esc-prop-battery learning curve. I had a Emax Grand Turbo 2215-15 1,470 KV electric motor on a slow stick. I am using a 2 cell, 1300 mah battery with it and an 18A ESC. I believe I was flying a 10.6 prop. It flew fine and I was happy with it. I broke one of the motor mounts so I ordered another mount.. In the meantime , I want to put a Turnigy motor (2370) rated at 1300kv on the same slow stick usnig the same battery. According to the KV rating, there is going to be around 1200 rpm difference between the motors. This difference between the motors with the way that I fly shouldn't be a problem. I guess I am asking if the prop is being turned at about the same rpm, shouldn't the plane fly about the same (less the rpm difference? )

Thanks

aeajr

My Feedback: (2)

First, this should be VERY helpful:

EVERYTHING YOU WANTED TO KNOW ABOUT ELECTRIC POWERED FLIGHT
http://www.rcuniverse.com/forum/m_7100376/tm.htm

kV is a rating of the speed the motor wants to turn per volt applied. So a 1300 kV motor wants to turn 30% faster than a 1000 kV motor when the same voltage is applied.

Now we add the prop, the load. If you put the same prop on each motor and the same battery the 1300 kV motor is going to draw more amps because it is trying to turn that prop 30% faster.

Is that bad? Well it might be.

If the motor can't handle that much amperage it will be damaged.
If it pulls more amps than the ESC can provide it will be damaged.
If it pulls more amps than the battery can safely provide then it will be damaged

Typically as we go up in kV we go down in prop size or pitch to maintain the same amp draw.

Note that power is stated in Watts. Watt= volts X amps. So a 11.1V battery driving a motor that is drawing 10 amps is delivering 111 watts.

Note that you can have a motor that is 1000 kV rated for 5 amps, another 1000 kV motor rated for 20 amps and another 1000 kV motor rated for 100 amps. All the same kV rating but VERY different power ratings. Very different watts but all with the same kV rating. The higher amp motors are typically spinning bigger props.

Read the book at the link above and it will make more sense but I hope this helps.

Dr Kiwi

If that is a 28g Turnigy 2730 versus a 59g E-max 2215.... you will get considerably lower RPM because of lower Kv, but even lower rpm than that because a tiny motor won't be able to swing a large prop as rapidly as a heavier motor could.... and you'll only be able to put half as much power (Watts) into the prop anyway.

jollycub

My Feedback: (5)

Thank you. This should be very helpful.