Motor selection

[Fly Boy 3]

As an electric newbie I have tried to read as much asI can before asking silly questions.

  As a ic nut of over 50 years of flying, I could eye up a model, put a 40,60 or 90  motor plus right size prop and away to go. Not so with electrics lol.  Ok, for a start I use  the80-100w /lb for motor. I would like to use a 3s battery and appropriate sized esc. What I need now is a KV NUMBER TO FLY SPORT PLANES.  Would this be low around 950 1500 kv. I would then try a selection of props and a watt meter.  THANK YOU.

[Shaun Walsh]

33 minutes ago, Fly Boy 3 said:

As an electric newbie I have tried to read as much asI can before asking silly questions.

  As a ic nut of over 50 years of flying, I could eye up a model, put a 40,60 or 90  motor plus right size prop and away to go. Not so with electrics lol.  Ok, for a start I use  the80-100w /lb for motor. I would like to use a 3s battery and appropriate sized esc. What I need now is a KV NUMBER TO FLY SPORT PLANES.  Would this be low around 950 1500 kv. I would then try a selection of props and a watt meter.  THANK YOU.

It depends upon the type and size of model.

A small fast delta foamy with a pusher prop might need a 2200kv motor with a 5 inch prop.

A large slow trainer might need an 850kv motor with a 12 inch prop.

It also depends upon the current rating of the motor. Unsurprisingly,  motors with a higher current rating can turn a larger prop than a lower rated motor assuming that they have the same kv rating. 

I use propCalc to determine the best motor/esc/prop combination. 

[Duncan Disorderly]

https://www.ecalc.ch/setupfinder.php

[Philip Lewis 3]

1 hour ago, Fly Boy 3 said:

As a ic nut of over 50 years of flying, I could eye up a model, put a 40,60 or 90  motor plus right size prop and away to go. Not so with electrics lol.

There is a quick and dirty way to do this, E Flite motors are labelled as IC equivalents so a power 60 is equivalent to a .60 glow etc etc, and they cover pretty much the whole range from power 10 all the way up to power 160, just look at the can length KV and diameter and look for an equivalent the same if you don't want to pay E flite prices, 4 Max also have a chart for E Flite equivalents. Likewise Hobby King do or used to do the same with their easy match range i.e. G90 equivalent to a .90 glow.

 

The E Flite data sheets will give you suggested prop sizes.

Edited March 20 by Philip Lewis 3

[Simon Chaddock]

Of course by far the best starting point is to use a recommended motor and prop for the plane! 

 

But if you want to select one yourself the motor supplier usually has a typical prop selection giving the prop, pitch and thrust of each. Even if you chosen supplier does not a Google or Ebay search is likely to show one that does. The motor may have several kV options and that may be in the list as well.

From your past knowledge you will know what prop, pitch and rpm you might expect from a suitable IC so as a start you could select a motor with a kV and prop that gives as similar rpm. With electric rpm is kV x voltage say 11V under load for a 3s..

With electric there are many variables so there is always a bit of "suck it and see" to get the combination that best suits how you want to fly.

Just remember "over prop" an IC and it just does not perform well but with electric something will burn out. "Under prop" IC and it may over rev and do mechanical damage but with brushless electric you can even take the prop off and it will do harm at full power.

 

I could suggest that with IC in RC the motors are all "detuned" for throttle response and reliability to such a degree that within the 2 & 4 stroke categories there is little difference between the effective power from the various manufacturers. It was not always like this. 😉   

 

[Fly Boy 3]

Thanks all for your valuable information. It’s a bit of a learning curve for me  but I’m on the way due to my forum friends.  Cheere

[Cuban8]

Selecting the components for an electric setup is not difficult but does require a certain amount of electrical background know-how that some folks are either not interested in or find hard to grasp. Not suggesting that FB3 falls into that category of course.

A good alternative is to take a look at the comprehensive list of recomended setups for various models on the 4-Max website https://www.4-max.co.uk/recommended-setups.htm and find a similar model (or if you're lucky the same one) to that you wish to build or convert and go from there. You'll be well within the ballpark as regards power etc and perhaps only a slight change in prop size might be needed to match things up perfectly.

Edited March 21 by Cuban8