1104 motors but which kv?

[aburn09]

 I'm looking for some new 1104 motors for my latest micro build but I'm a little confused as to what kv I should go for ?
Just as an example if I chose a motor from this Banggood page should I go for higher or lower kv ? Some are around 5000kv where others are 7000kv which should be better ?
I'm going to be running a 3s battery.

https://m.banggood.com/search/1104%20Brushless%20Motor.html

[Cheredanine]

Props mate?

[aburn09]

 :embarrassed   oops yes might help if you knew the props I was running which are Gemfan 2035 
This is the micro stack i'm using......
http://vi.raptor.ebaydesc.com/ws/eBayISAPI.dll?ViewItemDescV4&item=142513855807&category=182213&pm=1&ds=0&t=1507175242000&ver=0&cspheader=1

These motors were a possible option too ?
https://m.ebay.co.uk/itm/4x-EMAX-RS1106-4500KV-6000KV-7500KV-MINI-Brushless-Motor-RC-FPV-Racing-MINI/172816261014?ssPageName=STRK%3AMEBIDX%3AIT&var=471598752804&_trksid=p2060353.m1438.l2649

[Paul01]

 Hi aburn09,

Have a look at fpvmodel.com they have dragonfly 1105 7500kv which are awesome on gemfan 2035 quad blades. They are also very well made motors.

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[Elmattbo]

For 3s I’d say as a rule you’re looking at the ~7000kv ones. I’ve got the 4500kv emax but that’s on 4s.


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[aburn09]

I already have emax red bottom motors on my 5" and it does give it a nice punch out.......So if I went with the emax 1106 they come in 4500,6000,7500kv I assume the higher kv will give better performance but less flight time than if I went with the 4500kv ?
I will be flying with 3s.......but the set up could take 4s ? 

[Elmattbo]

Not quite. You need to match the kv with the battery and prop. As a rule, you need to drop the kv with higher cell count batteries or they will burn out with the higher current draw. Also more aggressive props will demand higher current too.
With micro builds, 3s and even 2s can perform really well, particularly since higher cell count batteries weigh a lot more.
However, if it’s 4s your after then you probably need the lower kv ones. I have read people use the 6000kv ones on 4s, but they won’t last too well and you’ll have to be careful with props.


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[aburn09]

Thanks Elmattbo I realistically will only be using 3s so with the gemafan 2035 as a maximum angled prop I'll be using I'll probably go for the emax 7500kv motors 

[mo_miah]

whats the rule with quad motors kv - battery V - props?

with RC cars we aim for set rpm (30-50k rpm max) at the pinion/motor and gear for torque/speed
if the motors cant handle the gearing we gear down or drop kv and increase the supply the voltage

[Cheredanine]

As a basic rule the cell count of the lipo governs the voltage

The motor kv is the rpm per volt it will try and spin at when at wide open throttle

The prop puts load on the motor, how much load depends on the weight o& the prop, the number of blades, the pitch of the blades, the flexibility of the blades and the shape of the blade. That is a lot of variables.

The load on the motor from the props makes the motor need more force, force comes from electrical power, which means the motor drags more amps and ultimately won’t meet the target kv

Just to complicate it even more, as the motor increases the rpm and it’s amp draw increases, the lipo tries to provide this, and in doing so the voltage sags, a# the voltage sags, the speed the motor tries to hit drops etc

A lot complex varriables there that can not realistically be modelled.
So you need some sort of reference.
Manufacturers specs help however they are not always accurate (understatement)
Manufacturers like xnova understate their specs so you are very safe and the motors will outperform expectations. Less reputable or cheaper motor manufacturers overstate to make their motors seem appealing, this can result in underpowered quads or burned out motors

So a far better reference is independent thrust tests.
For 5 inch quads the undisputed god of this is Ryan Howell and miniquadtestbench.

For smaller quads the best I know of is Engineerx who runs a YouTube channel with tests (and also posts on rc groups)

Get the test, match the motor and prop, look at the thrust and amp draw for your cell count. Bear in mind you have 4 motors and you will lose something like 30% off the amp draw in the air rather than on the bench. Then make sure your lipo can handle that.

Also watch the review, Engineerx is pretty good at pointing out sweet spots and the quality of motors, just because he tested a motor or prop combo doesn’t mean it is a good idea and he will point it out.

[daich]

those rs1106 are heavy and amp hungry.  if you're going 2" and will be around 60-70g I'd go 1104 7500kv on 3s
once you get 90-100g then you should go 1106 but at that weight I would go 2.5" or even 3" prop

edit: I'm talking final weight before adding the battery