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Suggestion: Episode regarding brushless motors and esc´s.

#1
There is a common doubt between us, the noobs.

Will this "XX" Amp ESC run my "YY" without burning him? How far i can go im AMP´S? What happens if i have a powerfull motor and an small ESC?

Most of times when we go after a new power set, we need to dig thousands of webpages after suggestions from others, but what if we could figure in advance wich is the best and the maximum configurantion a brushless motor can take?

Please, share your toughts!
 

ananas1301

Crazy flyer/crasher :D
#2
That is true. It would make a good episode for those still trying to get into thoses sizes, so mostly beginners.

After while when you keep looking at power systems you kinda get a feel of what motor which size should have etc.

But I think it would make a nice educational episode.
 

SunShine

not crazy, just stupid
#3
I support the idea of a motor focused show. showing us how to rewind the motors to different kVs and eventually even try to make a motor with switchable kV (by making multiple windings and switching between serial and paralleled connections, have never done it myself, but should work in theory. then you could make a plane where you first learn to fly it slow with a big prop and when you learned that, then you can by a smaller higher pitched prop and fly fast). but thats just an idea.
-so please don't make it just for the beginners, there is already allot of that on the web.
 

ananas1301

Crazy flyer/crasher :D
#4
I support the idea of a motor focused show. showing us how to rewind the motors to different kVs and eventually even try to make a motor with switchable kV (by making multiple windings and switching between serial and paralleled connections, have never done it myself, but should work in theory. then you could make a plane where you first learn to fly it slow with a big prop and when you learned that, then you can by a smaller higher pitched prop and fly fast). but thats just an idea.
-so please don't make it just for the beginners, there is already allot of that on the web.
I'd appreciate that version a lot!!!
This was it still will be interesting for both beginners and advanced pilots. Good suggestion SunShine!
 

jdog1001

Junior Member
#5
I would really appreciate an episode that goes over picking a motor, specifically from hobbykings.com site. How do you go about picking a motor when you know you need 700w of power, just as an example.
 

pgerts

Old age member
Mentor
#6
I would really appreciate an episode that goes over picking a motor, specifically from hobbykings.com site. How do you go about picking a motor when you know you need 700w of power, just as an example.
This is what i had done (just did it actually):
The motor is for an "ordinary" plane, not a really slow flyer or a fast (jet).
If I want 700 W a can get something for a 3 cell Lipo with about 70 Amp or something for a 4 cell Lipo coming down to 50A - (lower amps are normally preferred).
I need a motor for about 700W
I need a controller for minimum 50 A and more if i want 3 cells.
I need a battery .... I want to fly 10 minutes but not on max power. 3000 mAh 4 cell will give enough at 20C but i want to fly in the winter so i choose 40C.
I go to HK and brushless motors by sice 46 and larger.
What to choose? I am a light flyer so i sort by weight and find The 480G as a possible choice - but slightly big with 1000 W
480G.jpg
Go back to outrunner by size - 15-40
15-40.jpg
Check the first one - Donkey 194 grams with 680W 11*5 prop.
donkey.jpg
Limited to front mounting and need a collet adapter.
Next down in the list is Turnigy 3542 130 grams with 1250 KV and 8*6e prop giving 800W according to Frank´s review
tgy3542.jpg
OK my plane is a light combat/pylon trainer so i choose the Turnigy. If i had a high wing trainer/cub the choice would have been the Donkey with lower revs and bigger prop. Both are about the size i wanted. The Turnigy can be mounted in front of or behind the fire wall and comes with a collet adapter.

The controller :
40-79 Amps will be something to go from.
esc.jpg
The first is the red brick - it will be fine. 5A bec will be more than needed for my small plane.
rb.jpg
But i have a lot of Turnigy Plush that have worked perfect for me many years.
The 60A will also be a good choice. 3A bec is perfect but for my combat/pylon trainer i will get the red brick.

The battery:
Well - after many years and a lot of batteries i go directly to the nanotech and select 4 cell.
nt.jpg
the size already selected give me a 4 cell 3300 mAh battery for 42 dollars - expensive.
An alternative could be the Zippy Flightmax 4s1p 40C for 29 dollars.
33.jpg

I need 4 mm bullet plugs to the controller.
http://www.hobbyking.com/hobbyking/store/__9283__HXT_4mm_Gold_Connector_w_Protector_10pcs_set_.html
I need some shrink tube and soldering help to finish the job.
Some propellers according to the reviews. This is a lot of power - i do not want any slow fly or GWS props to this motor.

This is just one of many possible ways to select a working motor-esc-battery.
 
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nibnobsam

I like big leccy planes
Mentor
#7
The advantage of HobbyKing is they list the maximum current, recommended voltage and kv of the motors. Other sites I used before discovering HK just listed the size of the motors instead of the current and even often listed the wrong specs for a motor. (p.s. josh and josh, use current and power instead of amperage and wattage:D)
 

teflyer

Full Circle
#9
I would really appreciate an episode on matching battery, esc, and motor also.

Right now my method to matching esc and battery is look at how thick the wires are on the battery and the esc, which depends on how much current the battery can output and how much current the esc can handle, and if the wire thicknesses are close, the battery and esc most likely will work together without making the esc very hot! :)

For the motor, I just look at Hobby King's information as noted above. :D
 

pgerts

Old age member
Mentor
#10
Right now my method to matching esc and battery is look at how thick the wires are on the battery and the esc,
That is one way but not the best.

You need an ESC that can cope with the highest currents the motor will take.
The problem might be that the motor can be overloaded with a to big propeller or trying to run the motor if the propeller is stuck in the grass or something. The best is if you can get an ESC with enough but not a lot more amps than the motor.

An example :
The Hextronic 24 gram "indoor motor". The specification says max load 7 A (and load current 9A).
You will typically run 6 minutes on a 300 mAh battery.
10C tells that you get 1/10 of an hour = 6 minutes. 10C on a 300mAh tells that your load is 3A from the battery.
That is if you are using your motor with an average of 3A but can burst up to 7A (or more if your propeller is stuck or over sized).
To be on the safe side i would choose an ESC for 8A or 10A or 12A. Anything bigger than that is dead weight and normally loss off efficiency. (some will say that a bigger esc have lower internal resistance and less losses).

You need a battery that can supply the maximum current the motor will take.

In the example with the Hextronic 24 gram motor i need a battery that can deliver 7A continuously although i will normally only need 3A. This i can get from a 1C 7000 mAh battery (you will not find a 1C LiPo), I will also get the same current from a 10C 700 mAh battery or a 20C 350 mAh battery (or a 40 C 175 mAh battery).

Another question is how long time i want to fly on a battery.
As seen in the first example most people don't run the plane on maximum power all the time if it is not going to hover.
I want my flights to be about 5 minutes if i am flying pattern (loops, rolls, spins, wing-overs a.s.o.).
If i am flying a motor glider (thermal) then i am using 100% power but only for maximum 30 seconds every 4 minutes or so.
If i was flying FPV then i would perhaps wanted a battery for longer flight times. An FPV is often draggy and heavy with all equipment and will also need power for the extra camera and transmitter. Get a big battery to that kind of flying.

Aeroplanes normally fly better if they are light so i will use 2 or 3 batteries to replace rather than one battery 3 times as big.

As for the C-rating, more C is often an indicator of quality. Hi C means low internal resistance in the battery - cooler battery - less losses in heat and better when it is cold.

Wire thickness :
This is something that is hard to get if you are an electrician used to the "standards" in AC home cables.
In a plane you will normally run more than 10 times the current in the same wire as you have in your home.
Reasons are : short distances, short time with highest currents, good cooling, "gold" connectors.
You don't want to thin wires as the can get hot (and give you losses). You don't want thick wires as they are heavy.


 
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colorex

Rotor Riot!
Mentor
#12
Thanks from me as well, pgerts!

The Hextronic 24 gram "indoor motor". The specification says max load 7 A (and load current 9A).
You will typically run 6 minutes on a 300 mAh battery.
On a tri, would this mean that a 1300mAh battery would last about 8 minutes?
 

pgerts

Old age member
Mentor
#13
On a tri, would this mean that a 1300mAh battery would last about 8 minutes?
You can never tell the amps on a copter unless you know the total weight and the drag. It is better to measure "live".
1300/3 gives 433 mAh per motor. I assume that you can get 70% of that with a Hi C battery (nanotech) before the voltage is going down to much. If you need 6 amps then you will get about 3 minutes of good flying. I would go for something like 2400 mAh for a tri but i think you shall drop undcon a question as he has a lot of experience in multicopters need of power.
 

ananas1301

Crazy flyer/crasher :D
#14
Thanks from me as well, pgerts!



On a tri, would this mean that a 1300mAh battery would last about 8 minutes?
You will have to take into account that you won´t be flying your Tricopter on full throttle all the time. Let´s assume you´ll be pulling 3 A out of each motor while hovering. (should be around midstick, I didn´t want to take 3,5 as I can´t be bothered to calculate :D )
So 9A in total constantly.

With a 1300mAh battery this would mean that you:
If you are contantly pulling 1,3A you´ll have a flight of an hour.
If you are taking out of it roughly 9,1A you´ll have probably a seventh of the time because 1,3*7 is 9,1 which is approximately 9)

A seventh of an hour is something around 8,5 Minutes if my head isn´t wrong. So you´re right Colorex.
 

colorex

Rotor Riot!
Mentor
#15
Yeah, that's kind of what I expected. Though I'll probably test my Bixler's battery time by running full throttle with a timer, and then see when the ESC cuts off. That will be my flying limit.

I read somewhere that you shouldn't run the motor up without letting the plane go, and that you shouldn't run the motor without a prop. Is this true?
 
#16
I think the prop puts some load on the motor so there will be increased current going into the motor.

So if you want an accurate runtime of the battery with the full setup, I think you would leave the prop on.

However, if you want to see if the setup is working properly, i.e. right motor direction, I would suggest leaving the propeller off to be safe.

Also check out this Flitetest episode at 11:57


If you have the prop on, never let go of the plane.:D
 
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colorex

Rotor Riot!
Mentor
#17
I think the prop puts some load on the motor so there will be increased current going into the motor.

So if you want an accurate runtime of the battery with the full setup, I think you would leave the prop on.

However, if you want to see if the setup is working properly, i.e. right motor direction, I would suggest leaving the propeller off to be safe.

of course I may be totally wrong since a fast moving prop is dangerous. :p

If you have the prop on, never let go of the plane.:D
Yes (thanks) but is it OK for the motor?
 
#18
Do you mean will the motor be okay if the prop is not on it while you run it up or do you mean will the motor be okay is the prop is on it while you run it up?
Either way I would think so.
 

colorex

Rotor Riot!
Mentor
#19
Do you mean will the motor be okay if the prop is not on it while you run it up or do you mean will the motor be okay is the prop is on it while you run it up?
Either way I would think so.
Actually, both.

I think motors start screaming if running without load... But if you say so... Thanks :)
 

pgerts

Old age member
Mentor
#20
Yeah, that's kind of what I expected. Though I'll probably test my Bixler's battery time by running full throttle with a timer, and then see when the ESC cuts off. That will be my flying limit.

I read somewhere that you shouldn't run the motor up without letting the plane go, and that you shouldn't run the motor without a prop. Is this true?
Running your plane at full throttle with a timer will not give you anything useful.
The average power to the motor is normally less than 50% of full throttle.
Better is to put your timer on 10 minutes and fly "normal" then see how much there is left in the battery when done.
Much of your flying will be cruising or even better getting a thermal and gliding.
You will be warned in good time when flying.
1 - the ESC will reduce power to the motor so that you will "feel" when there is little left to bring your plane back.
2 - the ECS will cut of the power - then you have to turn down the throttle stick 2 seconds and slowly start again to get your plane home.
* - there will always be enough power left in the battery for the receiver and servos several minutes after the power to the motor has shut down.

The reason not to put the prop on is that you shall not accidentally harm you when setting up the plane.
The motor will not "scream" or something bad if there is no prop.
You will also need the prop on to determine the rotational direction unless you are really good at looking at hi speed rotating things. It is hard to get the motor to rotate really slow so you can see the direction.

IMPORTANT - put the prop on in the right direction - backwards normally have a lot less efficiency.

Running the motor up to 100% without letting it go before start is smart - you will see that everything is working fine.
Starting at half throttle and then advancing to rise and realize that you have forgotten to put the newly charged battery in the plane can be "annoying" if starting in the wrong place and have no place to land straight forward ;-)
 
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