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  • September 20, 2019, 06:56:21 AM

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Author Topic: Brushless motor  (Read 640 times)

Offline cory colquhoun

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Brushless motor
« on: August 18, 2019, 08:52:00 PM »
Hi all, wondering higher or lower Kv for control line stunt ?

Offline Crist Rigotti

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Re: Brushless motor
« Reply #1 on: August 18, 2019, 11:07:30 PM »
KV depends on the number of cells you wish to use.
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Offline cory colquhoun

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Re: Brushless motor
« Reply #2 on: August 19, 2019, 02:50:09 AM »
KV depends on the number of cells you wish to use.
I have 4s 2700 batteries which I would like to use , but get a little confused when it comes to motor choice, I have an eflite 15 in an accentor and it performs well , was after a suitable motor for a Cardinal I have almost finished approx weight 45 -55 oz flying weight , maybe a cheaper brand from hk

Cory

Offline John Rist

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Re: Brushless motor
« Reply #3 on: August 19, 2019, 07:46:27 AM »
I have had good luck with Cobra motors.  Priced in the $40 to $60 range.  A 4 cell setup needs a KV in the 900 to 1000 range.   I have 3 Cobras right now.  A 3529/10.  KV 980 @ around $58.  It is in a SV-11.  I have a 2820/12 KV 970 @ $43 and a 2826/10  KV 930 $49 in a pair of Cavalier.   All work well on a 4C setup.   Good bang for the buck.

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Offline Tim Wescott

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Re: Brushless motor
« Reply #4 on: August 19, 2019, 09:15:27 AM »
Hi all, wondering higher or lower Kv for control line stunt ?

High or low depends on how you hold your mouth.  You should size the system so that when the battery voltage is hovering around 3.3V or 3.2V per cell and you still need lots of poop in the overhead 8 and the clover it's there.  For a fixed-speed setup (Hubin & KR timers) you want your set speed divided by Kv to be about 75% of your nominal pack voltage (meaning, pack voltage computed at 3.7V/cell).  For variable-speed setups like the Fioretti and Burger timers you want more (because they ask for more speed when the airplane is on top), but I'm not sure how much.

If that works out to "high Kv" for you, then you want "high Kv".  If that works out to "astonishingly low Kv" for you, then you want low Kv.

You probably do want a higher cell count for a motor than is typical or recommended for RC -- the recommendations for motor/prop combinations in the catalogs assume that at some point you'll nail the throttle to the top of the transmitter and bore holes in the sky.  With a typical top-level competition stunt setup, this would burn out the motor or ESC.  It works for us because the timer/governor combinations we use keep the motor from running at full throttle until the end of the flight, when the battery is starting to go flat.

If this is all making you want to scream and run around the room bouncing off the walls, just look in the "list your setup" thread, and pay attention to the timer used, the number of cells, and the Kv of the motor.  Then copy something that works.
« Last Edit: August 19, 2019, 02:26:38 PM by Tim Wescott »
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Offline cory colquhoun

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Re: Brushless motor
« Reply #5 on: August 19, 2019, 10:15:49 AM »
I have had good luck with Cobra motors.  Priced in the $40 to $60 range.  A 4 cell setup needs a KV in the 900 to 1000 range.   I have 3 Cobras right now.  A 3529/10.  KV 980 @ around $58.  It is in a SV-11.  I have a 2820/12 KV 970 @ $43 and a 2826/10  KV 930 $49 in a pair of Cavalier.   All work well on a 4C setup.   Good bang for the buck.
https://innov8tivedesigns.com/
Thanks John ,will check them out!

Offline cory colquhoun

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Re: Brushless motor
« Reply #6 on: August 19, 2019, 10:23:14 AM »
High or low depends on how you hold your mouth.  You should size the system so that when the battery voltage is hovering around 3.3V or 3.2V per cell and you still need lots of poop in the overhead 8 and the clover it's there.  For a fixed-speed setup (Hubin & KR timers) you want your set speed times Kv to be about 75% of your nominal pack voltage (meaning, pack voltage computed at 3.7V/cell).  For variable-speed setups like the Fioretti and Burger timers you want more (because they ask for more speed when the airplane is on top), but I'm not sure how much.

If that works out to "high Kv" for you, then you want "high Kv".  If that works out to "astonishingly low Kv" for you, then you want low Kv.

You probably do want a higher cell count for a motor than is typical or recommended for RC -- the recommendations for motor/prop combinations in the catalogs assume that at some point you'll nail the throttle to the top of the transmitter and bore holes in the sky.  With a typical top-level competition stunt setup, this would burn out the motor or ESC.  It works for us because the timer/governor combinations we use keep the motor from running at full throttle until the end of the flight, when the battery is starting to go flat.

If this is all making you want to scream and run around the room bouncing off the walls, just look in the "list your setup" thread, and pay attention to the timer used, the number of cells, and the Kv of the motor.  Then copy something that works.
  Helpful information thank you Tim.

Offline David Hoover

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Re: Brushless motor
« Reply #7 on: August 19, 2019, 10:25:37 AM »
Tim,
I think you need to divide "your set speed times Kv" by 1000 to get a number that makes sense relative to pack voltage.
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Offline Tim Wescott

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Re: Brushless motor
« Reply #8 on: August 19, 2019, 11:53:46 AM »
Tim,
I think you need to divide "your set speed times Kv" by 1000 to get a number that makes sense relative to pack voltage.

Kv is in units of RPM/volt.  All specifications for hobby products are loosy-goosy, but if you have a Kv = 1000 it should mean that the motor would turn 11,100 RPM on a 11.1V (3S, 3.7V) pack without a prop installed.

So, no, I don't think you need to divide by 1000 -- just keep track of units.
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Online Ken Culbertson

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Re: Brushless motor
« Reply #9 on: August 19, 2019, 12:24:57 PM »
I have 4s 2700 batteries which I would like to use , but get a little confused when it comes to motor choice, I have an eflite 15 in an accentor and it performs well , was after a suitable motor for a Cardinal I have almost finished approx weight 45 -55 oz flying weight , maybe a cheaper brand from hk

Cory
I am running a Cobra 2820/12 on a 51oz profile.  The motor performs flawlessly.  I run a 4s 2800 setup and have about 30%  - 36% at the end using a 11-6 three blade Master Airscrew prop.   The same setup running a 12-6 APC runs me down to 15%.  My point is that 2700 is cutting it close.  I run 5:30 to give me about 10 5.4 extra laps.  if I want to go around again.  5:20 would probably work out OK since I have never added 8 laps extra to a pattern. 

Ken
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Offline Tim Wescott

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Re: Brushless motor
« Reply #10 on: August 19, 2019, 01:00:28 PM »
I am running a Cobra 2820/12 on a 51oz profile.  The motor performs flawlessly.  I run a 4s 2800 setup and have about 30%  - 36% at the end using a 11-6 three blade Master Airscrew prop.   The same setup running a 12-6 APC runs me down to 15%.  My point is that 2700 is cutting it close.  I run 5:30 to give me about 10 5.4 extra laps.  if I want to go around again.  5:20 would probably work out OK since I have never added 8 laps extra to a pattern. 

Ken

This reminds me: any of this stuff is a starting point -- just like a new plane with a new engine, you're going to have to experiment with your setup to get it dialed in.
AMA 64232

The problem with electric is that once you get the smoke generator and sound system installed, the plane is too heavy.

Online Ken Culbertson

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Re: Brushless motor
« Reply #11 on: August 19, 2019, 01:36:27 PM »
Cory:

Not sure your original question got answered.  The range most of our mortors fall in is 700-1000.  Another FYI, I just received two 4s 3000 30c batteries I ordered to replace two aging 2800's.  I use Turnigy.  Not top of the line but they are still very good for the price.  I get about 50 cycles.  Point is that these batteries are 20 grams lighter at 3000 then the 2800's were.  Make sure you check the dimensions and weights.  They are all over the board.  I weigh every one I get and tape on some weights to make all of the ones I use for a particular plane weigh the same. 

Ken
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Offline David Hoover

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Re: Brushless motor
« Reply #12 on: August 19, 2019, 01:38:03 PM »
Kv is in units of RPM/volt.  All specifications for hobby products are loosy-goosy, but if you have a Kv = 1000 it should mean that the motor would turn 11,100 RPM on a 11.1V (3S, 3.7V) pack without a prop installed.

So, no, I don't think you need to divide by 1000 -- just keep track of units.

In this case, you need to run at about 8300 rpm to stay above 75% of pack voltage.  Which means it's set speed (in rpm) divided by Kv to find the resulting voltage.  I was having trouble understanding how you could multiply a number in the thousands (rpm) by another number that's about 1000 and get a number that resembled pack voltage.
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Best, Hoovie

Offline Tim Wescott

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Re: Brushless motor
« Reply #13 on: August 19, 2019, 02:27:32 PM »
In this case, you need to run at about 8300 rpm to stay above 75% of pack voltage.  Which means it's set speed (in rpm) divided by Kv to find the resulting voltage.  I was having trouble understanding how you could multiply a number in the thousands (rpm) by another number that's about 1000 and get a number that resembled pack voltage.

Thanks for catching my error, and being persistent about it.  I've edited the spot that I got wrong.
AMA 64232

The problem with electric is that once you get the smoke generator and sound system installed, the plane is too heavy.

Offline David Hoover

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Re: Brushless motor
« Reply #14 on: August 19, 2019, 03:03:21 PM »
No problemmo.
Life is simple. Eat. Sleep. Fly!
Best, Hoovie

Offline cory colquhoun

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Re: Brushless motor
« Reply #15 on: August 22, 2019, 08:40:48 PM »
Thanks for all the input guys, cobra motors seem hard to source here in oz unfortunately, so I have ordered a 3548 1000kv Turinigy to try on  the cardinal see how it goes

Thanks Cory

Offline John Rist

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Re: Brushless motor
« Reply #16 on: August 24, 2019, 02:15:05 PM »
Thanks for all the input guys, cobra motors seem hard to source here in oz unfortunately, so I have ordered a 3548 1000kv Turinigy to try on  the cardinal see how it goes

Thanks Cory
Looks like a good choice - should work.  What speed controller and timer are you using?  I have had good luck with the KR timers from RSM
      http://www.rsmdistribution.com/index.php
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Offline cory colquhoun

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Re: Brushless motor
« Reply #17 on: August 28, 2019, 03:51:55 PM »
Looks like a good choice - should work.  What speed controller and timer are you using?  I have had good luck with the KR timers from RSM
      http://www.rsmdistribution.com/index.php
Hi John, I have a pheonix ice lite 50, and an fm 9 timer, I wish to get more involved and learn more about ecl, will checkout that link ,

Cory


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