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        Discussion Cogging issue with Car BL Inrunner

#1 Beau0090_99 Dec 12, 2012 05:01 PM

Cogging issue with Car BL Inrunner
I have a Turnigy Sensored 9.5T inrunner that I have put in a car. I am using a sensorless ESC to spin it. When starting, the motor is really tough to get started. Once it starts moving, then it has power and seems to run smoothly. My question is if you suspect something wrong with the motor, or is it the fact that I have a sensorless ESC conencted to it? I have the same ESC in another car with a sensorless motor in it and it runs smoothly. I am on the fence between it being a design issue with the sensored motor/sensorless ESC or a bad winding. I took the motor apart. Each winding is wrapped around a singly tooth on the stator(not sure the proper term). The rotor has one single north and one single south pole. Wuld this be a 2 pole motor then? It seems unimagineable that this could spin. I haven't seen something with so many poles.

I welcome your feedback.

#2 modisc Dec 13, 2012 12:22 AM

you need to post pics of the winding. and show how many nodes are there on the stator. Normally it will be distributed winding ,rather than concentrated windings as you indicated: each coil takes one tooth.

#3 Beau0090_99 Dec 13, 2012 07:42 AM

That's what is strange. This one has three nodes on the entire stator. Each phase is wound around one node only. I thought it was strange too.

#4 jackerbes Dec 13, 2012 08:46 AM

That is this in runner here, right?


As I understand in runner motors, the windings should be slightly over lapping each other and wrapped around the inside of the "can" or motor housing. And the rotating part is the magnets so count the number of those will tell you the pole count.

Each of the magnets will have a North pole on one end and a South pole on the other but the pole count will be the number of magnets, not the number of N and S ends.

Can you do some basic trouble shooting with a multimeter? If so, check the resistance on the three terminating lugs (1-2, 1-3, 2-3) and see if they are all the same and that they have steady readings. And then check each of the lugs for shorts to the housing.


#5 KenSt Dec 13, 2012 11:36 AM

Sounds to me as if you have a two pole three phase, one tooth per phase motor. This combo can be found in the chart at post #4 of this thread. It is the least number of poles and teeth possible for a three phase motor.

I believe this combination runs a little rough because the two "on" phases are not symetrical to any other phase as would be the case of a winding around say six teeth.

As a result, I would try a sensored controller with it. It should eliminate the start up stutter typical of a sensorless control.

#6 modisc Dec 13, 2012 03:17 PM


Originally Posted by Beau0090_99 (Post 23516221)
That's what is strange. This one has three nodes on the entire stator. Each phase is wound around one node only. I thought it was strange too.

Then nothing is strange.
3N2P is using concentrated winding. winding factor is 0.866.
That is why you need to post pics, or states everything clear.

#7 KenSt Dec 13, 2012 03:32 PM

I'm just assuming that is what it is from his description. I have no first hand knowledge of this motor. Even so, Turnigy instructions say it can use a sensorless ESC. Maybe it really can't???

#8 Beau0090_99 Dec 13, 2012 07:10 PM

Thanks all,
I thought that a 2 pole motor would have two magnets on the rotor, with 2 sets of North and 2 sets of south poles. This thing only has one magnet on the rotor. The rotor is integrated. I wonder if it got magnetized wrong at the factory. I took readings with a multi-meter, but then pulled it apart. All of them were stable and there did not seem to be a short to the stator housing. I am going to rewind it anyway, just to increase the kV a bit and if there was a hi-pot short that I couldn't detect, then hopefully I can remedy that.

Jack, that is the correct motor. The motor is (was) capable of moving, but severely stuttered, and sometimes would not get started at all, unless you gave it a bit of a kick.

Thanks again.


#9 Beau0090_99 Dec 13, 2012 07:29 PM

2 Attachment(s)
Here are some photos of the stator and rotor.

#10 modisc Dec 13, 2012 08:13 PM

6 Attachment(s)

Originally Posted by Beau0090_99 (Post 23521284)
Here are some photos of the stator and rotor.

THere you go. it will be much clearer to post pics. The motor looks well, a good 3N2P inrunner. The rotor which is one-axial magnetically charged to be a 2-pole rotor, is mechanically favored. This type of one-piece rotor is very commonly seen in servo motors. In servo inrunner motors, the rotor can be 3-axial charged or 4-axial charged to be a single magnetic rod of 6-pole and 8-pole respectively, which has a sinosodial magnetic property.

I thought these servo motors, used ones, are also cheap in US. But just now i looked at ebay, these stuff are sold quite expensive. The third pic showing an 8-pole rotor, is a 100W tamagawa servo motor, which cost only 15-25 USD in China but much more on ebay. This rotor is a perfect fit for Neu 1515 sized stator, given the air-gap to be only 0.2mm.

#11 KenSt Dec 14, 2012 08:42 AM

Hi Curtis,
the rotor can't be magnetized wrong. The magnetizing field around the magnet during magnetizing MUST be North and South. However, as Modisc pointed out, they can be magnetized with multiple poles. The easiest way to check is to get a magnet and go around the rotor. It should pull and repel as it passes over the poles in the rotor. Your only possibilities are one North and South or two. (4 pole)

#12 gkamysz Dec 14, 2012 08:55 AM

Which ESC was being used? Do they have a good reputation for starting this type of motor? Did you try another ESC? Such a simple motor is not likely to have a fault especially if the only issue is startup.


#13 Beau0090_99 Dec 14, 2012 05:29 PM

It only has one North and one South. My thought was that it was meant to go into a 4 pole motor and was magnetized in a 2 pole magnetizer. I am using the Trackstar 60A sensorless ESC, and I don't know if they can startup a motor like this very well. One thing is that it doesn't have any adjustable timing, which I thought might help. I'll see what I can come up with, I have a couple of airplane ESC's I can try at least as a test. I only have the Trackstar ESC for a car.

#14 hoghead5150 Dec 14, 2012 06:54 PM

it's normal.

from my experience with brushless truck/car motors what you are seeing is normal.

usually the sensored brushless motors have a little less timing in them. this retarded timing is not a problem IF your running sensored esc and a sensor cable. the sensors help smooth out the start up and usually if set up right there is virtually no cogging.

with a sensorless motor there is a little more timing in the motor. this advanced timing helps startup but it still will have slight cogging compaired to a sensored setup.

the gearing in the truck/car can also either help or hurt cogging. the higher geared the vehicle the more cogging you will usually get. the lower geared the less.

#15 KenSt Dec 16, 2012 12:19 PM

Sensors are the norm and required in many industrial applications for brushless motors. They provide maximum torque at a stalled condition just like a brushed motor and won't switch to the next set of phases until the rotor gets there. Ideal for RC cars.

Sensorless works in RC planes because we don't care if the motor stutters SLIGHTLY at start up and the prop doesn't need maximum torque to start spinning.

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