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Old 05-14-2017, 11:06 AM   #1
john kruger
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help please

im a definite beginner although ive built models for many years
i had looked at a program me to assist me to pick power options and props but i coulnt make it operate any advice were i can find a program-me made for dummies lol

cheers
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Old 05-14-2017, 11:51 AM   #2
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When I was starting into electric set ups, http://headsuphobby.com/
was one of the biggest sources for info. Their motor and prop data gives you a very good idea what style, weight and flight characteristics, most of the motors they sell, will support.

Welcome aboard John!


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Old 05-14-2017, 12:57 PM   #3
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+1 on Heads Up. Send them a note about what you're doing, and they can suggest a motor, battery, prop, and ESC for you.

For general info, though, it's hard to beat this:

http://www.wattflyer.com/forums/showthread.php?t=31071

What goes up, must come down. The trick is to keep it in one piece.
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Old 05-14-2017, 04:44 PM   #4
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Originally Posted by john kruger View Post
... im a definite beginner ...
...

Originally Posted by scirocco View Post
While an absolutely critical part of the system ...
Kv is actually the item one should choose last.
  1. Decide your peak power requirement based on the weight of the model and how you want to fly it.
  2. Pick a preferred cell count (voltage) and pack capacity for how to deliver the power.
  3. Pick a prop that will a) fit on the model and b) fly the model how you want - often as big as will fit is a good choice, but if high speed is the goal, a smaller diameter higher pitch prop will be more appropriate.
  4. Look for a size class of motors that will handle the peak power - a very conservative guide is to allow 1 gram motor weight for every 3 watts peak power.
  5. Then, look for a motor in that weight range that has the Kv to achieve the power desired with the props you can use - a calculator such as Ecalc allows very quick trial and error zooming in on a decent choice. For a desired power and prop, you'd need higher Kv if using a 3 cell pack compared to a 4 cell pack. Or for a desired power and cell count, you'd need higher Kv if driving a smaller diameter high speed prop compared to a larger prop for a slow model.
The reason I suggest picking Kv last is that prop choices have bounds - the diameter that will physically fit and the minimum size that can absorb the power you want. OTOH, combinations of voltage and Kv are much less constrained - at least before you purchase the components.

So Kv is not a figure of merit, in that higher or lower is better, it is simply a motor characteristic that you exploit to make your power system do what you want, within the constraints you have, eg limited prop diameter if it's a pusher, or you already have a bunch of 3S packs and don't want to buy more, and so on.

Minor lay-out changes by RvS
So ...
What plane? Weight? Span? Type? Link?

Prettig weekend Ron

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Old 05-14-2017, 04:47 PM   #5
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Originally Posted by john kruger View Post
... i had looked at a program me to assist me to pick power options and props ...
You need a bit of prior e-flight knowledge to use those e-calculators, otherwise, as with all software, garbage in, garbage out.
Because current is proportional to voltage squared, and proportional to Kv cubed, and because power is proportional to voltage cubed and Kv⁴, little changes in input voltage, battery resistance or Kv can have a huge effect on output numbers.
e-flight calculators (compilation) (sticky)

Also, calculators will only get you in the ball park, always check a new/changed setup with a watt-meter. Without one you're in the dark, until something starts to glow.

Some well-structured reading and handy e-tools for rainy/windy days. Will save you, and us , a lot of questions. Notably the 'what went wrong?' kind of questions
Will also prevent you from burning up several controllers and/or motors and/or battery:
E-flight primer and tools

And please, do your RC equipment, wallet, ego, battery, controller, motor, house/garage/car a big favour ... get a watt-meter. It will more than pay for itself, will save you at least one fried motor and one fried controller. Will also help you finding the optimal setup.

Vriendelijke groeten Ron

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Old 05-14-2017, 05:17 PM   #6
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https://ecalc.ch/motorcalc.php

...... simple and does the job.

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