Help with Tiger motor selection

[Eggbeater]

I have narrowed my motor selection for my 925-950 scratch built Hex to two Tiger motors. MT3515-15 (400kv) and MN4014-11 (330kv). I am leaning towards the MN4014. Looked at the specs and ran some eCalcs. They seem pretty close. Anyone wanna help me decide?

Some details: 6S 12000mah 35C, 40a ESC's, WK-M, Flying weights: 5.5kg naked...7.5kg max'd. 15.5 CF props seem most effecient but I really like my 14x8 Graupners for stability and stength on an S800. FYTI, I didlose 1.5min or so of flight time with the Graupners but so far worth it.

 

[Bartman]

what do the charts at the Tiger site say about efficiency of each motor at the target hover RPM for each motor?

 

[Eggbeater]

Bartman,
Tiger uses diff. charts for the two motors. One lists 50%-100% THROTTLE (so I read the 50% line) and the other doesn't break down the throttle but lists 1-14 settings for the amperage (so I used #7 hoping it was 50% throttle). I am listing these results as "Tiger" below and also listing eCalcs. In all cases, the MT3515-15 seems more effcient. You agree? On heli's I have an approx target headspeed. Not sure what you mean by target rpm so I listed both the 50% thottle hover as well as compared like/kind rpm's.

MT3515-15
Tiger. 50% throttle. 14x4.7 prop. 4045rpm. 10.27% and 0.36% effciencies
eCalc. Used same variables for both motors. 88.9% effeciency at Hover

MN4014-11
Tiger. 50% amp (mid chart). 14x4.7 prop. 4520rpm. 8.49% and 0.30% effeciencies
Comparing similar rpm's to above 4065rpm 9.37% and 0.33% effeciencies
eCalc. Used same variables for both motors. 69.7% effeciency at Hover

 

[Bartman]

i generally design to a target hover weight and then size things from there. divide your target 7.5 kg by the number of motors and then go to the charts to find a motor that is running in the 50 to 65% range while generating your target-per-motor thrust.

 

[Eggbeater]

Bartman,

You just scrambled my brain. I used two target weights for all of my calculations...5.5kg (fun fly) and 7.5kg (max payload). I then compare motor charts or eCalc's to see which motor has the best effeciency, flight times and a few other things I understand. Such variables as RPM vs. Amperage vs thrust vs prop sizes etc go beyond my current gray matter. Too much thinking and not enuff flying. Ha. Based upon all I see, the MT3515's outperform the MN4014. Now one may have bigger and better bearings or something else I don't know.

With all due respect can you just answer my stupid question? I know you are really trying to help with my overall understanding but you only have so much to work with here (me). I was hoping for a "I like the xxxx motor because xxx" kinda answer.

 

[Bartman]

with a name like eggbeater, i'd guess your brain comes pre-scrambled, no?

if 7.5kg is your target weight on the high end, then 7.5/6 is what each motor is going to have to carry when hovering. It should happen around 65 to 70% throttle.

It sucks that
A. there isn't complete data for the MN4010 using 6 cell packs
B. the Tiger website is so freakin' slow!

I'd go with the MN4012-11 motors with their 30A ESC's. The ESC's don't have a BEC so you have to bring power to the receiver some other way, I'm pulling 3S power through the balancing tap and using a regulator to bring it to a level the receiver can handle.

The MT-3515 motors are powerful but they're heavy compared to the MN4012 motor. I've got 4 of the MN4012 waiting to go on a quad and 2 of the MN4010 on the way so I can run them on the bench and see what they do with 6S packs.

Good luck,
Bart

 

[Eggbeater]

Yes. The scrambled brain did not come on suddenly. It took years to get this way.

Did you make a typo? What happened to the MN4014-11? You don;t like it? Why the 4012-11 instead?

Was planning on using the WK-M's regulator for RX/Controller circuit.

 

[Bartman]

what weight will you fly at most often? the 14 in MN4014 means the stator in the motor is 14mm high, the 12 is 12, the 10 is 10. the 14 makes more power but if it's power you don't really need then it's just excess weight and the 12 is sufficient. i tend to be weight obsessive so things have to be simple and light or have a really really good reason for not being simple and light to make it onto the heli. big motors don't go on unless there's a pressing reason to have them. you said 7.5kg max for a hexa, i think the MN4012 will get you there and they're lighter than the MT3515.

for the Rx, power is power so get it wherever it's appropriate.

 

[helloman1976]

i generally design to a target hover weight and then size things from there. divide your target 7.5 kg by the number of motors and then go to the charts to find a motor that is running in the 50 to 65% range while generating your target-per-motor thrust.

Good one, never thought of it that way but good one. I have recently learned, thanks to help from users on this forum, how to use eCalc. Think that might help here?

 

[Eggbeater]

Very cool and thanks BARTDUDE for the education. I will consider the MN series and 40 series but take into account the stator size and weight. Good to know. Will be getting back with results too once this thing flies. Money and /or parts always welcomed. Ha.