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Author Topic: OH MY! Electric Motors Can get so confusing?  (Read 1477 times)

Offline Kevin Muckleroy

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OH MY! Electric Motors Can get so confusing?
« on: December 25, 2018, 08:51:00 PM »
OH MY! Electric Motors Can get so confusing
IE: Brodak BH-2076 aka: Electric Motor 2826 aka:C-35-48) KV950.
RSM Black Tiger Advertised as BK3548C 900kv but when you get it is marked as 950kv
Both of these motors appear identical. number of magnets and poles. length and diameter
Erics RSM Designations make sense. Why duz Brodak have so many different descriptions for the same size motor?
What I am getting at is some one will be talking about a Brodak 2826 so in my mind be thinking its 28mm diameter by 26mm length when its actually 35mm diameter by 48mm length.
Someday I will get to understanding all this E-Power stuff. Too stubborn to give up on learning
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Online Fred Underwood

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Re: OH MY! Electric Motors Can get so confusing?
« Reply #1 on: December 25, 2018, 08:59:54 PM »
Here is a place to start

https://rcdude.com/cobra-c-2826-10-930kv-brushless-motor.html

Find the "28" and "26," for their classification and then look at outside motor dimensions.  Then realize that not every manufacturer or seller uses the same system.  Look at weights and outer dimensions and kv's and you can eventually get an idea.  Or find a brand and learn that system.  For reasonably priced motors, Cobra seems to work well front mounted.
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Offline Mike Haverly

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Re: OH MY! Electric Motors Can get so confusing?
« Reply #2 on: December 25, 2018, 10:40:53 PM »
Good advice Fred.  I try to pay attention to kV, dia and watts.  That usually keeps me out of trouble.  Or I just ask someone who knows!
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Mike

Offline Target

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Re: OH MY! Electric Motors Can get so confusing?
« Reply #3 on: December 26, 2018, 05:23:35 AM »
I think some measure the outer case and some are measuring an inner part of the motor.
That causes your confusion. And I'll agree that THAT is confusing.
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Offline Jim Mynes

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Re: OH MY! Electric Motors Can get so confusing?
« Reply #4 on: December 26, 2018, 06:21:32 AM »
The “Industry Standard” is that there is no standard.
I have struggled with the same head scratching confusion, having bought Arrowind, RSM, Turnigy, and Cobra motors for one reason or another.
Since I’ve had great results with Cobra motors I decided to settle on that brand, and I have my four favorite sizes that I know will fly a given size airplane.
I’ve also settled on 4S batteries (although I’m open to 5S if needed) and Castle Creations Edge Lite ESCs.
Timers are a different story. I find it hard to choose between KR or Hubin timers, they both work very well and have good features.
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Offline Kevin Muckleroy

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Re: OH MY! Electric Motors Can get so confusing?
« Reply #5 on: December 26, 2018, 09:50:44 AM »
T-Rex E-Conversion post newer than 2010?
Trying to figure out from the 3 motors I already have which combo would work best in a T-Rex. Prefer a 4s system (Have 8 batteries from 3500mah to 3800Mah)
BUT If better off with 5s no problem going that way.
Also willing to buy different motor if 4s is viable?

Motor Choices:
Brodak BH-2078 3520 / 950kv
RSM BK4250C / 750kv
Scorpion SII-3026 / 710kv

No Clue on Prop size 12x6E?

Useing:
ZTW 65a ESC
KR-2 Timer/Governor
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Offline Target

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Re: OH MY! Electric Motors Can get so confusing?
« Reply #6 on: December 26, 2018, 11:21:50 AM »
I would suspect that you will want to stay with 900KV with a 4S battery.
The 700 kv's would likely be better with a 5S I would think.
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Chris
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Offline Tim Wescott

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Re: OH MY! Electric Motors Can get so confusing?
« Reply #7 on: December 26, 2018, 11:55:32 AM »
  • Some companies classify by outer dimensions of the rotor, some by the dimensions of the armature.
  • Two identical motors with different windings can have the same power ratings, but different Kv ratings (basically, if you fill the available space with copper the motor will have the same power in to power out behavior, but with everything scaled as a function of the number of turns)
  • If a motor is built as light as possible using iron, copper, and the strongest magnets around, its power/weight ratio will be the same as the next motor over.
  • El-cheapo motors will have el-cheapo bearings, less precise machining, and el-cheapo methods of fixing magnets in place.  Caviat emptor -- and buyer beware of vendors speaking Latin!

Bottom line -- most motors on the market have around the same power/weight ratio.  Which, unfortunately, I can never remember.  I always have to go look at half a dozen motors on the web and re-calculate it.  But if you have two motors that weigh about the same, they're going to have about the same power capability.  If you have two 3522 motors that have markedly different weights, then one is probably an outside-dimension motor, and the other's probably an armature-dimension motor.
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Online Fred Underwood

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Re: OH MY! Electric Motors Can get so confusing?
« Reply #8 on: December 26, 2018, 03:38:18 PM »
IIRC, T-Rex is in the 650 square inch range.  That size plane can do well with 6 cell packs, and about 700kv motors, my preference.  Cobra 3520 700kv works well.  5 Cell and Cobra 3520 820kv or perhaps 700kv.  You are getting more watts in a fairly light battery in the 2700 - 2800 mah packs going from 5 to 6 cells.  4 cells can work also, so you have lots of choices.
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Fred
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Offline Jim Mynes

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Re: OH MY! Electric Motors Can get so confusing?
« Reply #9 on: December 27, 2018, 12:46:14 PM »
Quote from: Kevin Muckleroy on December 26, 2018, 09:50:44 AM
T-Rex E-Conversion post newer than 2010?
Trying to figure out from the 3 motors I already have which combo would work best in a T-Rex. Prefer a 4s system (Have 8 batteries from 3500mah to 3800Mah)
BUT If better off with 5s no problem going that way.
Also willing to buy different motor if 4s is viable?

Motor Choices:
Brodak BH-2078 3520 / 950kv
RSM BK4250C / 750kv
Scorpion SII-3026 / 710kv

No Clue on Prop size 12x6E?

Useing:
ZTW 65a ESC
KR-2 Timer/Governor

I would use the Brodak motor. Brodak’s web site says they used that motor on the SV-11 which has almost identical wing span and area as the T-Rex. Combined with your 4S 3500 and a 12x6E prop you should have a winning combo.
That Brodak motor is nearly identical to the Cobra 3520/10 that I bought to put in my SV-11 ARF. I haven’t put it together yet, but I expect it to be a good match.
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Offline Kevin Muckleroy

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Re: OH MY! Electric Motors Can get so confusing?
« Reply #10 on: December 27, 2018, 01:30:16 PM »
Quote from: Jim Mynes on December 27, 2018, 12:46:14 PM
I would use the Brodak motor. Brodak’s web site says they used that motor on the SV-11 which has almost identical wing span and area as the T-Rex. Combined with your 4S 3500 and a 12x6E prop you should have a winning combo.
That Brodak motor is nearly identical to the Cobra 3520/10 that I bought to put in my SV-11 ARF. I haven’t put it together yet, but I expect it to be a good match.
That is what I was thinking about the SVII. It is worth a try. They both have the same mounting pattern on "X" Bracket. And I have to make a new Bulkhead to mount either anyway.
Build it to fit 4s, 5s, and 6s Battery and just get some flying in. Woild like to change it to a nose mount with a Hunt Mount.
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