DropDz

Hey all, first post. I am just getting into RC flight as of the last two weeks or so. A friend of mine has been very helpful, but I'm lacking some info.

I've been looking around and can't seem to find study material on the relationship between the motor/propeller/voltage/thrust.

For example:

How many RPMs will a given motor spin with a given voltage?
How many amps does it pull with a given prop?
How much thrust does it offer with everything combined?
When are you overloading your ESC?
When are you overloading your Motor?
When are you overloading your face? [:@]

ANY info would be GREATLY appreciated. In return... uhh... I'd reccomend you buy a steak and McCormik's Montreal Steak seasoning, and Lea and Perrins worschestehershershire and cook a big ole fat meal.... with mac & cheese.... with broccolli in it.

Thanks a bunch all mighty people with.... neurons. Man, do I stutter.

packyj

With a brushless motor you can see how many rpm's the motor will spin with a given voltage by looking at the rated Kilovolt rating... or Kv. If a motor says it has a 1000 kv rating it will produce 1000 rpm's for every volt of power it receives. By looking at the battery you will be powering this motor with you can then calculate roughly the rpm's the motor will turn.

The amps the motor pulls will vary with each different size prop you use.

thrust is best measured with a thrust stand made of equal length dowels at 90 degrees to one another and a digital scale. One end holds the motor/prop combo whilst the other end rests on the scale. Powering the motor tells you on the scale how many ounces of thrust you are producing.

Overloading the esc happens by drawing more amps from the battery to the motor than the esc can handle. Most esc's will shut down when this happens while others will just over heat and become useless and/or in some cases actually catch fire.

Most motors have a voltage range listed on them... pretty straightforward here. Stay under the recommended voltage and you will be okay.

Over loading of the face usually occurs at all-you-can-eat buffets... which has amazingly still not led to the all-you-should-eat buffet

I may or may not have this information listed correctly as I'm not thinking too clearly at the moment... others will post and show me if I am incorrect I am sure

An invaluable tool to use when calculating your planes setup is a wattmeter. I use the watts up meter and have enjoyed it so far. It will tell you how many amps, volts, etc you are drawing in real time... it is very useful especially when hunting for that perfect prop.

jdetray

Good info from packyj, with one exception. The kV rating for motors does not stand for "kilovolt." In this case, the "K" indicates that we're talking about a mathematical constant.

Otherwise, the explanation for kV is pretty good, though it should be noted that the kV rating is a no-load specification. That is, kV = RPM/volt without a prop.

In general terms, motors with a low kV are useful for spinning a relatively large prop at low RPM with high torque. This is good for slow flyers and 3D-type planes where thrust is important.

Motors with a high kV are useful for spinning a small prop at high RPM with low torque. This is good for fast-flying planes where speed is important and also for gearbox applications.

Both RPM and current (amps) will vary with the prop being used. As you increase prop size, RPM will decrease, and current will increase.

- Jeff

DropDz

Amazing! That made sense! I know it's kinda basic but I just wanted to see what some of y'all know about this stuff. I like to be detailed and I can never seem to move on if I'm missing one little thing.

One more question, though. Obviously you have too much power when you turn a rudder mid-flight and start an oragomi hobby. But besides that, is there ever too much power (with the proper ESC and reinforcement of course)? Or do you have to build a larger scale to use a larger motor? I'm not looking at the weight aspect of the motor, just thrust.

For example, let's say I have a slow flyer and slap a fat brushless on it and reinforce EVERYTHING and use a little of that 3 cell lipo topping. Will it become a 10 times better plane, or will it just go into orbit? Speaking of which, I should put my phone number on all my planes just in case on hits an honest guy's house.

Thanks alot, you guys put a rung in my jungle gym.

--Matt

DropDz

Better yet, a super small park flyer, if brushless would fit, would it ruin the flight characteristics if it were over powered?

jdetray

What do you mean by "better?"

If you make a plane heavier, it will have to fly faster to stay airborne. Pretty soon, a slow flyer won't be a slow flyer any more. It might still be a fun plane, but it won't have the gentle, floaty characteristics we associate with a slow flyer. So if you want a true slow flyer, keep it light, no matter what kind of motor you put in it. (Actually, it would be more accurate to say "keep the wing loading low," but you get the idea, I'm sure.)

- Jeff

DropDz

Well, better was a bad choice for an adjective. You still answered my question though. Thanks for the insight.

Campy

My Feedback: (1)

What MAY help you with your questions is MotoCalc. You can D/L a fully operational copy of the program and use it free for 30 days - then you either have to buy it or go back to guessing

You plug in the info on the plane, then it will provide suggested motor/prop/gearbox ratios/batteries and give you a performance rating. You can also play "what if" with the motors, props, batteries, gear ratios, etc.

I have found MotoCalc to be about 95% - 98% accurate in its predictions.

Hope this helps.