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« on: June 25, 2018, 06:01:34 PM »
Imperial fire
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so i recently got new motors from a reputable brand. i had invested a lot and expected them to be top quality.

recently i decided to move to a 4 in 1 esc.. so i got rid of the separate esc and rewired the long wires.

i later observed that my motors were not spinning freely. i was FURIOUS. ' should have bought emax i thought to myself'

but there was no friction, no noise, just a resistance to spinning when spun freely. almost like a brake on a cycle. spend lots if time opening and cleaning all 4 motors. ( sometimes they would spin free sometimes they wouldnt , so  i just couldnt zero in on the problem)

found the devil - when the wires of the motors are connected to each other as shown in the pic, for some reason the motor brakes and when separated. they spin freely!!! simple as that.
i dont know what exactly is going on here but its a interesting find and had to share with u guys
 Hats Off

IMG_20180625_174710.jpg
eureka.... motor ocd cured.
* IMG_20180625_174710.jpg (35.56 KB, 448x336 - viewed 118 times.)
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« Reply #1 on: June 25, 2018, 06:16:09 PM »
shirsa2001
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Are those bullet ends soldered? they are open Huh?
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« Reply #2 on: June 25, 2018, 06:50:14 PM »
K K Iyer
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If those exposed joints can touch each other, imagine what would happen if the lipo was connected...
PLEASE COVER WITH HEAT SHRINK TUBE.
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« Reply #3 on: June 25, 2018, 07:34:43 PM »
Imperial fire
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Oh ...I am going to isolate them using heatsink tube ...I just took the motors off to resolder the long wire...
When I took em off and finished resoldering I realised that they were not free.

They will smoke my esc if kept like that..
(Image was just for representation) ...
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« Reply #4 on: June 25, 2018, 07:35:59 PM »
kiran rc
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@imperial fire
When you rotate the bell of the motor with hand, it induces a 'back emf'. Now, when two of the three wires are connected, the current in the coil increases which contributes to the resistance against rotation.

You may also notice the same observation after disconnecting the battery(even with battery connected) . In this case the capacitor in the ESC still remains charged and causes the mosfet to remain in the switched condition for a short period of time. Again, two of the wires get shorted and same phenomenon is observed.

For eg., consider delta/wye configuration.(Refer pic below)
1) wye-
Original resistance(b/w N1 and N2) -  2R/3 = 0.66R
New resistance after shorting - R/2=0.5R

2) delta
Original resistance - 2R
New resistance -3R/2= 1.5R

In both the case,  resistance decreases. From V=IR, current is inversely related to resistance.
Hence, there's increase in current.
magnetic field strength ∝ current
Due to greater field strength, braking torque increases.



images (2).jpg
Re: eureka.... motor ocd cured.
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« Last Edit: June 25, 2018, 10:44:11 PM by kiran rc » Logged
 

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« Reply #5 on: June 25, 2018, 07:50:46 PM »
K K Iyer
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@kiran rc
A meaningful clarification, as expected from you.

Would you consider rephrasing this part?
”the current gets shorted”
Regards
« Last Edit: June 25, 2018, 08:01:04 PM by K K Iyer » Logged
 

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« Reply #6 on: June 25, 2018, 08:29:37 PM »
Balakrishna Reddy
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@Imperial fire.
Whenever the motor rotates an emf is generated which is termed as back emf(so many things are going behind). Whenever the wires get shorted the back emf will lead to flow of current and thus creating an electro magnetic field counteracting the force(actual magnetic field) that created it(Lenz law). Due to this the motor is hard to rotate when the wires are connected to each other. This is same principle used in ESC designed for miniquads. You can check more about that here. Beautiful explanation
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« Reply #7 on: June 25, 2018, 09:03:36 PM »
Imperial fire
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.it's almost generating electricity like a little generator.

Interesting explanation...god only knows how many more incorrect assumptions I have about the things i use.
Should not have chosen arts.
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« Reply #8 on: June 25, 2018, 09:08:48 PM »
Balakrishna Reddy
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You are absolutely right @Imperial fire.
A BLDC motor/machine is both motor and generator. It is just how we use them. You connect the motor to a turbine and its a 3 phase generator and if you connect 3 phase supply(T&C apply) then its a motor.
So many things are happening inside motor and I don't want to confuse you by posting all those stuff.
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« Reply #9 on: June 25, 2018, 09:37:56 PM »
K K Iyer
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God only knows how many more incorrect assumptions I have about the things i use.
Should not have chosen arts.

Hit a very important point, knowingly or otherwise .
I do wish that:
Arts/Humanities students got some exposure to physics, chemistry and maths, and
Science/Engg students got some exposure to Economics, Political Science, Sociology, Accountancy etc
Some day, hopefully!
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« Reply #10 on: June 25, 2018, 10:48:57 PM »
kiran rc
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Edited reply #4 with more details.
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