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Numbers on Hobby King NTM motors

#1
What exactly do these numbers mean? I have an NTM 28-26 1200kv motor on my Bloody Wonder, Versa and Duster. I printed out the plans for my 2nd Versa at 130% so its slightly larger so I can load it with two batteries for longer FPV flight and carry my go pro in the water proof case in case I dump it in a body of water. I have seen where David put that 38-36 1800kv in the Speed Challenge but i wanted to work my way up in between those two motors. I understand what the KV does, but there are many on HKs web site. Can anyone explain what those numbers mean so I can make incremental upgrades to test out performance in the planes? Thanks again folks.

Oh and I do have a HK Mega Meter to test out motor/esc/prop combination and any input regarding that would also be great, thanks
 
#2
First number 28: is the stator or can diameter
Second number 26: is the stator or can length
In essence they are just basic info on size of motor, the more you get accustomed to seeing them the faster you can tell motor apart. Inrunners from outrunners and general idea of overall power of a given motor.

KV: is the the RPM per volt without load (i know you said you understood this but just rehashing)

Sometimes you will see a fifth number....for example a popular one....RCTimers 2826-6:
That last "6" denotes the number of wire turns around motor's pole. Basic rule of thumb on turns:
Lower number= higher top speed, less torque
Higher number= more torque, less top speed

I think you need to roughly work out what your all up weight will be on new larger versa with extra lipos. Even with a rough guess you can then sort out proper motor and prop combo.
 
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rcspaceflight

creator of virtual planes
#3
I know David explained exactly what those numbers mean once. I can't remember when/where. I want to say that it was the third podcast, but I could be wrong. I think the first number is the diameter of the motor and the second number is how many times the wire is wrapped around each pole. Basically, the bigger the numbers, the more powerful they are and the more power they require. But that's kind of obvious. Those numbers really aren't as informative as you'd think they are. They almost don't actually mean anything and are only for comparing.
 
#4
Once you have a basic idea of weight of new craft apply the following rule when choosing power plant.

70-90 watts/lb. Trainer and slow flying aerobatic models.

90-110 watts/lb. Sport aerobatic and fast flying scale models.

110-130 watts/lb. advanced aerobatic and high speed models

130-150 watts/lb. Lightly loaded 3D models and ducted fans.

150-200+ watts/lb. Unlimited performance 3D models.
 
#5
That all being said, that NTM 3836 1800kv is a monster motor. It powers my scratchbuilt 52" 68oz wing around on a 9x6 prop all day long without issue.

Wing in background behind 800mm pusher jet, just for comparison

IMG_0063.JPG
 
#6
You guys are AWSOME !!! thanks for all the input, I wish I could weigh it but I can't until I install the motor lol. I have several 3S 2200 packs, but I recently purchased two 3S 3300s as per Davids recommendation on the Versa Pusher conversion video. The 130% enlargement allows me to mount either 1 of the two stated batteries right behind the go pro, or even two on each side of the gopro within the wing behind the leading edge. Since the enlargement is a prototype, I understand I may have to cut it figuring this out until its structurally unsound to fly, but at $4 of DT foam board....... its aight, the second one will be the flight ready one. I am not sure if the 28-26 1800 will give me acceptable performance, my goal isn't blazing fast speeds, rather long flight times with a go pro H3, FPV transmitter and even an autopilot when the new Pixhawk is released. The reason for the slight increase in size os to be able to handle the payload and slightly better handling of wind
 
#7
Here are the pics of the internal layout so far of the 130% Versa, that battery is the 3300 and the second pic is the original sized Versa with the enlarged one in the back 1380201_10151780868456359_871700304_n.jpg 1383720_10151780738431359_338736916_n.jpg
 

Craftydan

Hostage Taker of Quads
Moderator
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#9
Rigo,

You *are* planning on taking out the battery *before* you glue up that monster wing, right?!? ;)

That looks like a nice build! looking forward to seeing $4 fly!
 
#10
#11
LOL yes Dan, I will be cutting a hatch to remove/install the battery(ies) into the fuselage. Of course with the two battery setup I will have 2 hatches adjacent from the camera
 

Craftydan

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#12
An additional question regarding the K-Force 100A ESC http://www.hobbyking.com/hobbyking/..._Force_100A_Brushless_ESC_USA_warehouse_.html used with the http://www.hobbyking.com/hobbyking/...Series_35_36A_1800Kv_875w_USA_Warehouse_.html motor, on the description it shows the motors max current is 65Amp but is paired with a 100Amp SC, what prevents the ESC from burning up with motor with 100A of power? do you have to program the ESC to top out at a certain point?

Very few ESC's are smart enough to current limit. Most ESCs will simply let the power flow until they burn out -- that's a fancy one, and will thermally limit (turn off if it gets too hot) but I wouldn't trust it to save the ESC from burning out. It's up to you to select and test the power system to ensure the prop isn't too hard for the motor to turn, The motor's draw won't be too big for the ESC and the current draw isn't too fast for the battery.

The positive side? So long as you don't over-prop that motor, that ESC should be happy with that motor.
 

Craftydan

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#14
Almost certainly, but I also wouldn't use a $60 ESC as a fuse to save an $18 motor.

If I were to choose which I'd rather burn out, the ESC or the motor, I'd choose neither. The way you pick that option, short of following other reported setups, is a Watt meter on a bench. Hard mount the motor on an arm, and connect up the meter. if you're over the spec'ed limits at WOT, or after 30s at WOT either is really hot, think carefully about stepping down the prop size.
 

vk2dxn

Senior Member
#15
Hang on a min...
If you have a motor designed to operate to a max current draw of 65amp max and powering it by a 100amp esc then it is a good combo. The esc will supply the current needed by the motor, What I mean by that statement is that if the motor only drew say 10amp then the "100amp" esc will only provide 10amp to the motor. Now my only advice for the setup that you intend to run is that you do not over prop the motor and cause it to draw in eccess of 65amp because you will let the magic smoke out of the motor.
 

Craftydan

Hostage Taker of Quads
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#16
Vk2dxn,

Agreed! It's a good combo, so long as the prop size picked isn't to hard for that motor to throw. (sorry, Rigo, if I wasn't clear)
 
#17
You guys are the greatest, vk2dxn stated it the way I understood, (kind of a newbie after returning to the hobby after 20 years and I never did electric) thanks to you both, I was just waiting for that answer since I was going to order that 100A esc and the 3836
 

rcspaceflight

creator of virtual planes
#18
Most ESC's over 30AMP don't have a built in BEC, be sure to double check and get a separate BEC if you need it. Otherwise you are going to fry your Rx instantly!
 

jetpackninja

More combat please...
Mentor
#19
The motor is what uses the amps- the motor draws the amp from the esc- if the motor/prop/battery combination can only pull 65amps
the 100 amp esc will only pass 65 amps.