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Old 08-25-2013, 08:47 PM   #1
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Question Matching Brushless Motors for Twins, Quads

Hi Everyone I Contacted Jeff at Heads Up Rc, to get some information on how to Match brushless motors for twins and Quads, Jeff Has a KV Meter that he can do that with, but he does not sell them, I was wondering if a Tach could be used to match Different motors with too, If anyone has any info on how to Match Motors with, Please Post it, and I am Sure it will help a lot of other people too, Including Myself Here is the Message that Jeff from Heads up Rc left. Take care and Have Fun, Chellie

Hi Chellie,
Nice to hear from you!
The easiest way to match two brushless motors to be used in a twin is to check the motor KV with a KV meter (we do not sell these, but they are available elsewhere).
Generally, it's not necessary to check the motor KV if the motors are from the same "batch". Motors from the same batch are generally very consistent in KV. Even if the motors are from two different batches, the difference in KV is not likely to be enough to cause a problem (though it is a possibility).

We have a KV meter at the shop, and we will check the KV of two motors for a twin if a customer requests it.

For quad copters, there really is no need to check the motor KV, as the flight control board adjusts the rpm of each motor continuously, and this automatically compensates for any difference in motor KV. There would need to be a very large difference in the motor KV to cause a problem.

We rarely post on the forums, but you can certainly share the comments above if you wish.
Best regards,
Jeff

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Old 08-25-2013, 08:49 PM   #2
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Cool but I must say after MANY twins matching KV closely is not important. I learned that when I started to play with differential thrust. It is AMAZING how much power you need to get that!

Quads - excellent idea!

Mike
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Old 08-25-2013, 08:53 PM   #3
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Thumbs up A Nice Find :)


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Old 08-25-2013, 09:01 PM   #4
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MAtch the motors and then the minor variations in the props will cause them to still operate at slightly different rpm...

The real goal is matching thrust.

It was proven long ago that having mismatched motors/engines on a twin wasn't all that big of an issue. Someone flew a glow power twin with a .40 on one side and .46 on the other. In fact when doing glow twins it is recommended to not even try to tune the engines identically... just tune each to run right.

With quads you'll be varying power to each prop in order to maneuver. Its unlikely for all 4 to be turning the same RPM at any time.
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Old 08-28-2013, 01:14 AM   #5
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Originally Posted by CHELLIE View Post
I'm just nit-picking for the sake of it, but the HK meter gives you only a "raw Kv" (no-load RPM/volts)...true Kv will always be somewhat higher. However, if you are using it to match motors, it will be fine since each motor will be measured by the same instrument, in exactly the same way!
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Old 08-28-2013, 09:55 AM   #6
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Thank You Everyone For Your Feed Back Great Information, Take care, Chellie

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Old 10-12-2013, 04:02 PM   #7
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Originally Posted by fhhuber View Post
.........In fact when doing glow twins it is recommended to not even try to tune the engines identically... just tune each to run right.....................
True as you don't want one to conk out as too lean or rich .... but that is not the end of the set-up ... as being a Glow flyer of years ago and recently started glow again ...

Once engines are set on their needles to run sweet ... you then harmonise the throttles so that each sings at similar RPM through throttle range ... What it basically comes down to is matching the engines at the fastest cruise setting ... accepting a slight inbalance at top end / bottom.

Easy to do without tacho if necessary - I had a tacho so was a doddle as I do now ... How ? Sound .... You know when they sing together as it's a definite sound change without the pulsing sound of out of step ...

If you really want to get deep into this ... then an old tape-recorder is the bees knees ... where it has the Magic Green eye for sound level ... watch the two green bits moving towards / away from each other ... Basically you have a probe mic and hold over intake ... adjust throttle for the magic green bars ... to match the same as the other engine ...

But of course as many of us did most of the time ... start the engines ... check they are similar on the tacho ... and fly !!

For my Twin Parkjet ... my laser tacho was used .. and no significant difference found ... well not enough to make me consider mucking about with it ! I fitted, connected up ... got rotation correct - I have contra props - and ran up against the tacho ... End of Story.

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Old 10-12-2013, 06:41 PM   #8
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Originally Posted by CHELLIE View Post
Thank You Everyone For Your Feed Back Great Information, Take care, Chellie

"Judge each day not by the harvest you reap but by the seeds you plant."

and gal, you plant a lot of seeds on here......thank you!
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Old 10-13-2013, 08:49 AM   #9
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Chellie, I've built and flown a number of twins and a four engined model all based on a basic 1800KV HK motor.
All are hand launched and none of them has an operating rudder, however, all are equipped with differential thrust.
I have to say that from my own limited personal experience with this type of model there appears to be no miss matched thrust issue at all and as rcers stated you actually have to apply a significant amount of differential to influence the attitude of the model in flight.

Barry
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Old 10-13-2013, 09:16 AM   #10
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Originally Posted by DEG View Post
"Judge each day not by the harvest you reap but by the seeds you plant."

and gal, you plant a lot of seeds on here......thank you!
Thank you for the complement

Originally Posted by baz49exe View Post
Chellie, I've built and flown a number of twins and a four engined model all based on a basic 1800KV HK motor.
All are hand launched and none of them has an operating rudder, however, all are equipped with differential thrust.
I have to say that from my own limited personal experience with this type of model there appears to be no miss matched thrust issue at all and as rcers stated you actually have to apply a significant amount of differential to influence the attitude of the model in flight.

Barry
Hi Barry Thats good to Know I have heard of some pilots having issues once in a while with mis Matched motors causing them some problems with more than one motor being used, and I was wondering if it would be a big issue with Quads, I Know the quads have a on board computer per say to control the motors and such, but i was wondering if a motor was to far out of KV Calibration how much that would affect a Quad to fly, The Quads are neet, I will have to make one soon Take care, Chellie

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Old 10-13-2013, 10:14 AM   #11
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Hi Barry Thats good to Know I have heard of some pilots having issues once in a while with mis Matched motors causing them some problems with more than one motor being used, and I was wondering if it would be a big issue with Quads, I Know the quads have a on board computer per say to control the motors and such, but i was wondering if a motor was to far out of KV Calibration how much that would affect a Quad to fly, The Quads are neet, I will have to make one soon Take care, Chellie[/QUOTE]

Me too! I'll have to have a go at one especially as it seems an obvious choice of machine for flying in the back yard and other limited spaces. It takes me a while to get around to something new though.
I hope you are correct in assuming that the on board computer can handle the differences in motor output.
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Old 10-13-2013, 10:20 AM   #12
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Originally Posted by baz49exe View Post
Hi Barry Thats good to Know I have heard of some pilots having issues once in a while with mis Matched motors causing them some problems with more than one motor being used, and I was wondering if it would be a big issue with Quads, I Know the quads have a on board computer per say to control the motors and such, but i was wondering if a motor was to far out of KV Calibration how much that would affect a Quad to fly, The Quads are neet, I will have to make one soon Take care, Chellie
Me too! I'll have to have a go at one especially as it seems an obvious choice of machine for flying in the back yard and other limited spaces. It takes me a while to get around to something new though.
I hope you are correct in assuming that the on board computer can handle the differences in motor output. [/QUOTE]



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Old 10-13-2013, 10:24 AM   #13
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Old 10-14-2013, 09:02 AM   #14
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Thanks for the links Chellie. Very informative tutorials;- makes taking the first step less of a giant leap.
Now it's definitely something to seriously consider doing.
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Old 10-14-2013, 02:30 PM   #15
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Originally Posted by baz49exe View Post
......
Me too! I'll have to have a go at one especially as it seems an obvious choice of machine for flying in the back yard and other limited spaces. It takes me a while to get around to something new though.......
Seems we are thinking same !! I look at the ones pals around me fly ... doesn't really get me excited - but as you say - small spaces etc.

Part of the reason why I went back into Helis ... and actually just bought a V911-1 micro heli.

I may have 3.5 acres (14,200 sq.m) of land - but with over 200 trees ... makes it impossible to fly anything else.

Nigel

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