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motor- esc- battery- formula

Old 09-02-2009, 07:37 PM
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jim34
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Default motor- esc- battery- formula

Could someone please explain to me (in layman terms) how I choose what motor with what esc and what battery. I have three 11.1v 910mAh lipos laying around and would like to build some Depron park jets or planes.
Old 09-02-2009, 11:15 PM
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tIANci
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Default RE: motor- esc- battery- formula

You want to make sure all 3 items match up to the amount of power that is being drawn. So nothing burns or fails. Now what affects the amount of power being drawn?

i. motor (size and KV);
ii. propeller size (diameter and pitch); and
iii. input voltage (how many cells).

You want an ESC that of course can handle the amount of amps and voltage. Your best friend will be a WATT METER and then to know what prop matches to which motor and how many cells you can use MotorCalc or read from the forums. Get info from those who have done it (and burnt it).

Smaller motors have a higher KV rating than the bigger ones
High KV motor can spin a small prop at very high speed or spin a bigger prop using less cells
Low KV motor is good to use when you want to fly with a big prop or want to use more cells with a smaller prop

I have the DualSky Breeze ES, the 2826-10 motor is 1,400KV and turns a 9x3.8 on a 3S 800 mAh pack. For a parkjet you want to turn something in the 5x5 to 7x6 range, depending on what type of plane and what sort of performance. So if you were to use the same motor size you want to take the KV up to perhaps about 1,700 for maybe a 8x6 or even 2,300 for perhaps a 5x5 prop.

Any headaches so far?
Old 09-04-2009, 09:51 AM
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ron_van_sommeren
 
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Default RE: motor- esc- battery- formula

* Choosing a power setup
http://www.rcgroups.com/forums/showthread.php?t=739069
http://www.wattflyer.com/forums/showthread.php?t=27019

* E-flight calculators, notably Web-O-Calc, D-Calc, MM_Calc (and derivatives) and Rod Badcock's calculators
http://www.rcgroups.com/forums/showthread.php?t=606703

* Get a current/Watt-meter, it will save you money and will more than pay for itself!
3$ diy Watt-meter:
http://www.rcgroups.com/forums/showthread.php?t=949923


For a rainy day ...

* Presentation: de-mystifying Electric Flight
http://www.rcaircrafters.org/The%20Electric%20Show.pdf

* http://www.ampaviators.com
-> Beginner Guide

* E-book: Everything You Wanted To Know About Electric Powered Flight
http://homepage.mac.com/kmyersefo/ev...ng-e-power.pdf
Corresponding discussion:
http://www.wattflyer.com/forums/showthread.php?t=31071

* Several Wiki's
http://www.wattflyer.com/forums/vbglossar.php

* E-flight calculators, a compilation
http://www.rcgroups.com/forums/showthread.php?t=606703

Get a current/Watt-meter

* http://www.ezonemag.com
-> Faq

* System wiring diagrams:
http://scriptasylum.com/rc_speed/_wiring.html
* LiPo pack and balancer cable wiring:
http://scriptasylum.com/rc_speed/_lipo.html

* Monthly Ampeer newsletter, on paper and online available. Excellent articles in the archives by e-flight pioneers Ken Meyers and Keith Shaw a.o.
http://homepage.mac.com/kmyersefo

Get a current/Watt-meter

* Brushless motor animations and simulations. Mostly outrunners but inrunners are just outrunners turned inside out, nothing fancy:
http://www.rcgroups.com/forums/showthread.php?t=216928

Get a current/Watt-meter

* Current, voltage, Watt, battery-types and -C-rating explained
http://www.rcgroups.com/forums/showthread.php?t=417868

Get a current/Watt-meter

* 'Dry' testing brushless motors after a mishap:
http://www.wattflyer.com/forums/showthread.php?t=35216
http://www.rcgroups.com/forums/showthread.php?t=240993

Get a current/Watt-meter

* How to repair a brushless motor
http://www.rcgroups.com/forums/showthread.php?t=1079423

Get a current/Watt-meter

* Motor_rewinding_101, about poles, winds, delta, star
http://www.gobrushless.com
-> knowledge base
-> basic overview (1-5)

* And I almost forgot, get a current/Watt-meter

Prettig weekend Ron
Old 09-07-2009, 07:52 PM
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Silver182
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Default RE: motor- esc- battery- formula

ron...

I have a twin vectored D/F SU-34 Full Back from Hobby Lobby...it flies great. The problem I'm having is Battery failures. It comes with a 4cell 3000ma 20c Lipo pack. Today I measured the Watts..close to 1000 actually 960. The amp meter said I was drawing about 63 amps.

OK I tried a Rhino 4cell 20c 3700ma pack today..and it provided almost full power for a full 4 minutes..something that I can not get out of the batteries that come with the SU-34. Both have 20c displayed on the pack but one is a much stronger and actually works.

What kind of battery pack should I be using for long lasting performance.
Lee
Old 09-07-2009, 08:13 PM
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speedy72vega
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Default RE: motor- esc- battery- formula


ORIGINAL: Silver182

ron...

I have a twin vectored D/F SU-34 Full Back from Hobby Lobby...it flies great. The problem I'm having is Battery failures. It comes with a 4cell 3000ma 20c Lipo pack. Today I measured the Watts..close to 1000 actually 960. The amp meter said I was drawing about 63 amps.

OK I tried a Rhino 4cell 20c 3700ma pack today..and it provided almost full power for a full 4 minutes..something that I can not get out of the batteries that come with the SU-34. Both have 20c displayed on the pack but one is a much stronger and actually works.

What kind of battery pack should I be using for long lasting performance.
Lee
Hey Lee, it's Rob. I'm the one who loaned you the 3700ma Rhino. I got home and finished charging that pack, it ended up taking 3112ma total, after the 4 min flight. That explains why your packs are dead already, it damages the LiPo cells if over-discharged. Your 4 min flight took the batteries all the way down, being only 3000ma capacity.
So, either one of two things: Either the designers of the plane never intended the plane to be flown at or very near full throttle the entire time, or their study on the proper capacity packs for the power system are flawed.
In either case, once you receive your 3700 packs, you should be ok as long as you don't go past your 4 min flight time, as there should be somewhere close to 588ma left in the pack, not over-discharged.
I also strongly recommend increasing the wire size from the ESC splices to the battery connector, as the increased resistance from the wires geting so hot will also stress your power system. In my opinion, 14ga wire isn't sufficient to sustain a constant 65 amp draw at over 15 volts, 12ga would be much better. You might even notice a slight performance increase also.

Rob.
Old 09-07-2009, 08:32 PM
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speedy72vega
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Default RE: motor- esc- battery- formula

Jim, sorry, I didn't mean to go off topic on your thread, I was helping Lee over the weekend with his plane.
In response to your question, what motor and ESC you choose to run with those batteries is going to depend first on the discharge rate of those packs, as this will kind of give you an idea of how much current they can deliver. A 3S 910ma pack is most likely going to be either a 10C or 15C discharge rate (you didn't specify), so to get a rough idea of your power available, 10C = 10x discharge rate = .910 amp x 10 = 9.1 amp constant. .910 amp x 15C = 13.65 amps constant. Next, you need to find a motor that operates within this range, and look at the wattage rating. That will kinda give you an idea of the total weight of the plane you can fly with it.
Generally, you want aroound 100 watts/lb for general trainer/sport type flying, 150 watts/lb for sport/light 3D, and 200 watts/lb and up for advanced 3D type flying. You can pretty much figure how much plane you fly with this info.
As far as the ESC, you will want to get one that can handle the current draw of your motor/prop combo. In other words, if your motor/prop draw 10 amps constant, you would be ok with a 15 amp ESC. You want to go a little bit higher capacity ESC than your system will draw to prevent burning it up.
You will definitely want to invest in a watt meter so you can see what your system is drawing. Changing props will significantly affect current draw, and it's very easy to overdraw and burn up your ESC or motor.
Hope this helps.
Old 09-08-2009, 09:49 PM
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Default RE: motor- esc- battery- formula

Hi Rob,
Thanks for the help this last weekend and for the detailed info here on-line...makes all the since in the world not to ever drain a LiPo down below it's rated capacity.
Lee
Old 08-11-2014, 01:39 PM
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