Interesting article that explains Electric stuff

[Trevor 25]

Ths article explained some things that I was confused about, might be useful to someone else.

 

http://www.gibbsguides.com/article51_Ho ... _campaign=[successful_Electrics_Issue_20]:_How_to_Choose_an_Electric_Power_System_

[Bravedan 106]

Well, having read both sections, twice, I can only say that I'm forced to disagree with some fundamental parts of it, especially the recommended order to choose the components.

 

Do I know better? Dunno, maybe not, but with eight years experience of modern EP, and currently over 150 EP models successfully built and flown, from ultra light indoor to brutal hotliner and ultra fast Delta, and only very rarely the need to revisit a set up after first choice, I must surely be doing something right?

 

One area I flinched over and started shouting at the screen ( ) was the recommended sequence of choosing a battery and Esc BEFORE the motor. Not in my lifetime it isn't! EP really is not that different to any other conventional tried and tested form of propulsion, and you don't set up any other by choosing the tank size first unless you have specific and abnormal space constraints!!

 

Then the 350W table that suggests as you want to go faster you either do not raise the kV or even lower it..............and at that point I wandered off shaking my head. A 930kV motor for a fast setup ? ? ....................

 

Here's just one example:-

 

The Mega 16 F5D brushless motor is designed for direct drive use in pylon racing models. When used with 11.1v 2200 or 3300 LiPo batteries and a Graupner CAM Speed 5.5 x 4.3 propeller, the current draw is around 35A.

 

Weight: 114g

Dimensions: 28 x 46.4mm

Shaft Diameter: 3.2mm

No Load Speed: 2650rpm/1V

Maximum Current: 50A

Resistance of armature: 7.5 mohm

Number of Poles: 6

Number of Winds: 2

 

Note:- 2650kV, 5.5x4.3, and a 35A draw, rather a long way from 930kV and a 10x10!!

 

Is it all off kilter then? Well no, but have to say I don't think very highly of it.

[Martin 0]

If you want something that shows all the possible variables in an electric power system and how they interact, have a look at the calculator on http://rcadvisor.com/. I've also got the book by the guy who runs this site and wrote the calculator, and it's pretty good on the subject of specifying electric power systems.

[alan 0]

Well, I only read the first page of the Gibbs Guide but I couldn't see anything wrong with it: It contains the two "rules of thumb" that will almost guarantee that a plane will fly ok (re. electric power)

!00 watts per pound as a starting point for power loading.

A battery with about 1/10 C of the expected max current.

 

What is more or less necessary then is to weigh the completed 'plane and to bench test it for power.

Bench testing by holding the motor in your hand is great fun but I once had a ESC fail and remain on full power! I had to put my knee on the battery so I could use my spare hand to disconnect.