? can anyone explain the relationship between battery motor and prop size?

Hi all! Just curious about the relationship betweens motors batteries and prop size.

I am running a HT-FPV that came with 4 of the DJI 2212 970kv motors and 8x45 props and 3s 3300 battery and I am getting about 10-11 mins flight time. However I still dont have the FPV camera or Tx yet.

The DJI motor actually is marked 3S 1045 4s 8045 which if I understand means that with a 3s battery it should fly with 10x45 props and 4s the props should be 8x45.

Ultimately I want as long a flight time as I can get but ultimately I will need lifting capacity as well.
Thanks everyone!

 

Big relationships here.

All starts with the aircraft, how big is it, what it weighs, what type of flying will it do.

Then you get to decide what motor / propeller combo will give you the lift and performance you want, followed by battery size to give you the flight time your looking for (that then adds weight for bigger battery sizes....so you kind of want to know this too.

Basically, larger props like slower motors. They are more efficient at making lift. Slower normally means less vibration and better for FPV / Photography

Smaller propellers can use faster motors, and in some cases give you the same lift or more as the bigger propeller. Great for aircraft that need fast stick response, stunt flying.

The same amount of lift (or more) can be had by using a 4S battery on the same motor with smaller propellers, as the motor has more volts the RPMs will be higher. The Kv rating means RPM per volt, to make it easy that DJI 2212 970kv will turn 970 RPM with a 1 volt battery, a 10 volt battery would allow the motor to turn at 9700 RPM.

A 3S battery has 11.1 volts, a 4S has 14.8 volts.

Using the calculators at http://www.ecalc.ch/ the lift of a 4 rotor Quad (as you listed in your question, 3S battery and 10 4.5 propeller) with the would be about 860 grams per rotor ( 3440 total). With 4 S and 8 4.5 thrust is 905 grams per rotor (3620 total).

Flight times are estimated at 15.1 minutes for 3S and 17.3 minutes 4S..............but this would depend on aircraft weight. More or less the same lift and flight times.

Using those calculators you can play around with different setups and find a good choice for what you want. Add bigger batteries, change controllers, see what happens with 3 blade props....on and on. You will also see when things can go bad as the calculator will tell you if the controller or motor will over heat, or the prop wont generate enough lift.