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Other › How do you know what the correct RPM is
02-09-2006 11:46 AM  12 years agoPost 1
JLundberg

rrApprentice

Denham Springs, Louisiana

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Hi everyone,

I had a question a while ago regarding my 1105 on 3s being hot. I was told to make sure I was running the correct rpm to get it in it's best work range.... How do I find the "correct rpm range"

Thanks ,

John

T-Rex 450X (modified), 450th, CC35, TP2100, CCPM, 9CHP,

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02-09-2006 02:51 PM  12 years agoPost 2
darrens

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United Kingdom

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If the transmission is free then what pinion are you running? Also be aware that a 3s system pulls high current which equals heat whereas a 4s system has high voltage but lower current draw and less heat.....4s is by far my preference for the Trex and has awsome power on my 1105 with a 9t pinion.

He who dies with the most toys is the winner!

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02-09-2006 06:08 PM  12 years agoPost 3
Showstopper

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pensacola, Fl

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I fly 4s on my motor. I run a 450th on 4s. While you fellas are de-maging your motor due to heat our stuff runs nice and cool.

Neil

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02-09-2006 06:19 PM  12 years agoPost 4
keyz

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, UK

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i goto agree with finless here
i run a 3s setup (evo 20's) with an AON 3500 13t which gives me excessive power , no bogging at all for 3D and i can only get battery/esc/motor luke warm
gives me plenty of power and 8 mins of flight time which i feel is plenty (could push it more but dont see the point)
i know this is not the motor the post is about but for a 3s setup is great and cost effective compared to 4s
this setup tac's around 2700 rpm if my tac works correctly !!!
sounds beastly on climbouts

If you need to get high , go and fly !

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02-09-2006 06:42 PM  12 years agoPost 5
Ozydego

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Westerville, Ohio

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Agreed about the 3s setup, My motor after a hard run is about 140° not nearly up to the 240° point where the magnets start demagnetizing... it sounds to me like a flimsy excuse to buy more expensive batteries.

Now, as far as JL's question, for most sport flying, you want to push for a 2400rpm headspeed. Now how do you get that... With a tach like finless suggested, or to get a fairly close number, use the headspeed calculation:

(Kv * voltage) * efficency rating * (pin / main) = headspeed

Specifically like for my setup... (3550Kv rating on my motor)times (11.1volt lipo) times efficiency (I use 85% or .85) times (pinion divided by main gear: 13 divided by 150) = my headspeed -->

(3550 x 11.1) x .85 x (13/150) -->
39405 x .85 x .0867 = 2904
Or roughly a 2900 rpm at 100% throttle....

Give or take 50 and your pretty close...

I have started to fly with a higher headspeed, , but if I were to use say an 11 tooth pinion, it would bring the rpms back down to the 2400 mark.

But Honey, I can't live with just stock.....

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02-09-2006 07:00 PM  12 years agoPost 6
JLundberg

rrApprentice

Denham Springs, Louisiana

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Thanks for all the info.

My motor was getting up to 140 during easy flying and I was worried if I was pushing it with 3s

I can't go 4s right now... I would have to buy chargers, lipos etc to go that road.

I know some of you are running the NEU 1107 on 3s with success and I was wondering if I made a mistake getting the 1105-3y

John

T-Rex 450X (modified), 450th, CC35, TP2100, CCPM, 9CHP,

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02-10-2006 10:36 AM  12 years agoPost 7
darrens

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United Kingdom

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Finless, your comment is treated with the contempt it deserves. Who would turn away from more power if it is a cost effective option and you have no idea of my flying capability. I'm not suggesting I am at any given standard, just that you have no idea where that is and should therefore reserve such comment.
Obviously by running higher voltage you get the same run times out of a lower capacity battery, so the battery cost is about the same. With the fact that neither the motor or battery are getting even warm, then it would be fair to assume this "no stress" condition will make them last longer that a 3s set up. All said and done, the 4s/3s comparison re cost is about the same, but the performance, well that's a different thing all together.

He who dies with the most toys is the winner!

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