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Old Jul 09, 2003, 01:21 AM
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gouch's Avatar
Lake Macquarie, Aust.
Joined Dec 2002
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need some thoughts on understanding motor specs

I posted this in parkflyers but with no response, thought this would be a better place.


I'm having some trouble deciding on a motor/ batt setup for a foam wing.

Its a taipan2, an aussie made ( i think) eps wing. 48"
I have one as a sloper and i have some cores to make an elec one from.

I want a faaast wing, not brushless fast, due to funds but here's where i get confused.

The speed 400/480 offerings from graupner seem hard to determine what is the go.

When looking at the charts on the specs what makes a fast power source?
Is rpm the most important?

The comparo between the 400 6 volt shows more thrust compared with the 480 BB yet the wattage? is higher on the 480.

But i'm sure the 480 would be more powerfull.
Am i confusing power and top speed? the fact that the 480 is pulling another 5000 odd revs would suggest it's the go.
What does thrust figure actually indicate?

How many cells? I understand the more cells the more rpm, but there obv. is a point were motor life and extra weight begin to detract from the performance from lesser cells?

As you can see i am totally confused with all this and even if you could post a link to somewhere explaining how to determine/understand setups would be muchly appreciated.

Should i go for two motors? I love the sound and i can get 2 sp400 motors for less than the price of a 480.
What size speed controller would 2 motors need, and how many cells would be advised?

WHAT WOULD YOU GUYS DO?



Cheers
Paul
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Old Jul 09, 2003, 09:11 AM
Balsa Flies Better!
Stamford, CT
Joined Oct 2000
6,719 Posts
You're doing it backwards.

Pick batteries and props first. Worry about pitch speed, not thrust- i.e rpm x pitch in inches relates to airspeed. Then pick motors. Most of us use watts to figure out which motor puts out more.

Sam
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Old Jul 09, 2003, 09:45 AM
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North Highland,ca
Joined Dec 2002
551 Posts
The brushed motor is measured in mm then add a 0 40mm + 0=
400 most of the time. Brushless normaly the diameter of the stator in mm then who knows sometimes thickness. CU
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Old Jul 09, 2003, 10:27 AM
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East Anglia, UK
Joined Sep 2002
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Speed 400's start to get hot and inneficient over 10A, the long can 480's will do 12A, and tend to like 8+ cells to do it on, whereas the Graupner 480's will do 15A plus, tho they really need 10 cells to do it.

The Graupner (sagami) 480 is a different class of motor altogether. Heavier, well made, good magnets etc. You need somethiong like 10xCP1300 or better to do it justice, but it will deliver the goods.

a 6x4 and 10 CP1300's will probably get you a screaming 50mph+ jet like plane: Stick a 3:1 box and an 11x7 on it and it will not be quite as fast, but will climb like a homesick angel.

2:1 and a 9x6 prop is between...fast and still bags of climb.

If its a powered sailplane you want, consider a 4:1 box and a 13x8 or 14x7 prop.
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Old Jul 09, 2003, 04:58 PM
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Lake Macquarie, Aust.
Joined Dec 2002
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Thanks guys, i'd like a twin setup if only for the sound!.
I would prefer to use DD to keep costs down so i'm thinking
from your reccomendations 2 graupner 480 with 10 CP1300 with the 6*4 props. Sound fast?


Are the cp1300 you are mentioning a sub c size?
[edit] I just found some half sub c cp1300. are these the cells
you reccomend?


I read somewhere else on these pages about using a single esc
what current esc would do this safely?

Also i read about fitting the motors in series, won't this halve the voltage to each motor? I would have thought parrallell was the way to go. or is it different than the light globe experiments we did in school?

Also has anyone used the permax 480? they are 13 grams lighter, a decent saving on 2, the price is $29 aus as opposed to the graupner which is $45 aus, so there is a weight and a decent money saving.
This web page from Peter Pine shows different shaft sizes, the graupner having a 3.2mm shaft to the permax 2.3mm. Now if this is the case do i need adapters to fit the props?

http://www.flyelectric.com/400motors.html

Cheers
Paul
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Last edited by gouch; Jul 09, 2003 at 05:14 PM.
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