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Old 03-11-2013, 02:27 AM
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kyleservicetech
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Location: Wisconsin, USA
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Originally Posted by fhhuber View Post
Look up the AXi 4120-18. on 6S it will pull about 45-50 amps with the correct prop.

Don't pick the motor by trying to match the glow power prop size it will be wrong for electric. You may need to go to a 3-blade for ground clearance.

I used a 4120/18 in a "60-90" size pattern ship with good results. I plan to put that power system into a King Kobra.

Use 2X 3S packs in series. You can then use the 3S for other planes too. I commonly fly planes that call for 3S 2200 mah with 3S 5000 mah packs. Just makes tjhem handle wind a little better :p

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Note: I have had very bad results with Turnigy motors... they get up to about 140F and the magnets come unglued.
Very bad when using a 5000 watt power system and a 22 inch prop

The AXi is fine at 150F
The E-Flite power 160 (same KV, same size, same weight) has no trouble with the same prop, esc and batteries as what destroyed the Turnigy motors.
You do get what you pay for...
IMHO, when your motors get into the multi-thousand watt range, you've really got to watch the motor's efficiency ratings. A program such as www.motocalc.com will give approximate info on this. The quality motors in this power range are running around 90% efficiency. Even so, with a 5000 watt motor, that is 500 watts of power lost in the motor itself. No matter what motor you are using, that motor had better have a lot of cooling air.

My opinion, especially with these larger motors, is, if the supplier does not furnish their motors winding resistance, go look elsewhere for a motor supplier. The winding resistance is critical with regards to motor efficiency, and it is quite easy to measure. (http://www.wattflyer.com/forums/showthread.php?t=50740)

A fairly safe rule on these larger motors is to run them at no more than 100 watts per ounce of motor weight. That would put the 5000 watt motor at around 50 ounces. Any mfg'r that claims 5000 watts with a motor that weighs 30 ounces is likely to have problems if the user actually runs their motor at the specified power level.
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