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Coreless Servos

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Old 10-10-2003, 10:23 AM
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Default Coreless Servos

What does that mean...Coreless? I assume it means something about the motor. Is this a good thing or bad?
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Old 10-10-2003, 11:50 AM
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Troy Newman
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Default RE: Coreless Servos

Coreless servos have a much higher quality motor in them...no brushes is a good analogy, but theres more to it. In general the motors are smoother, faster, and more efficient than those of non-coreless servos.

They are a better quality and last much longer. The high end servos with faster speed and more torque are usually coreless. This provides better resolution and precision than those of the regular motors.

The Coreless technology comes at a small price increase but is very much worth the advantages. I fly competition Aerobatics and can tell a huge difference in servo performance. The higher end coreless ball bear servos is all I use in my models. To me servo performance is very important. It makes my flying better and gives a better feel to the model.

The current crop of std servos is better than 10 years ago for sure....but the higher end servos really outperform the stds even in smaller 40 sized planes.

You will be able to tell the difference in servos when flying them. Also it is very important as the models grow in size that you get the right servo for the task. Many people use std servos because this is what came with the radio gear....These servos are not always the best for the application....once you leave the 40-60 sized models and go bigger or faster you need to look long at hard at servo choices....Just because the surface moves when you wiggle the TX sticks doesn't mean the servo will handle the loads in flight and perform as you need. Also you are sticking hundreds and in some cases thousands of bucks in it is it worth it to you to have enough power to realy do the job.

Sometimes undersized servos can lead to flight failures. You would be surprised at the number of modelers that build their dream model a P-38 100" span or a B-25 or the like and stick standard servos in it.....Then they have a failure and loose the model.


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Old 10-10-2003, 05:40 PM
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Default RE: Coreless Servos

If I am not mistaken:
Normal servos have several coil windings (poles) on the armature and permanent magnets along the outer case. This excessive wire is heavy. Coreless motors have magnets in the center and the coil wires are along the case. Coreless are lighter but cost more for the same power output. Also like stated above, since you don't have to convey power to the armature, brushes are not needed.
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Old 10-10-2003, 05:51 PM
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Default RE: Coreless Servos

Well, I ask because someone said I should get 57 oz torque servos for the flaps on my plane and I can't really find them. After the 44 oz standard servos, you have to go to coreless to get the next best price and they are like 3 times as much. I just need more torque....
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Old 10-10-2003, 06:02 PM
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Default RE: Coreless Servos

HiTec HS-425BB servos will put out 57 at 6v.

If you want the absolute best servo, coreless digitals
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Old 10-10-2003, 06:08 PM
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Default RE: Coreless Servos

No I don't...I want the next cheapest ones that will do the trick above 44 oz....but they are all like special function. I don't need digital servos for flaps that are usually set and forget....well thats all my radio is going to allow anyway.
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Old 10-10-2003, 09:27 PM
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Default RE: Coreless Servos

The JR DS811 servos would be perfect in a sport model on Flaps They are like 54-55in-oz of torque...non-coreless servos digital technology so they have great holding power and centering....And they are $48 each....this is a great setup at a really low cost... I would say these are the best solution if you're on the budget....another solution would be the JR531 Its $40 and has about 51 in-oz

Like stated before if you really want 57in-oz you can run on 6V 5 cell packs.

If 57in-oz is the goal you are very close with the 531's.....The 811's digitals will perform better as they have like 5X the holding power of a normal analog servo....This is important for flaps as they are usually large and hang down deflecting large amount of air and usually large flight forces applied to them...The 811's will be perfect.

Yes the cost is about double the cost of a standard servo but you are getting a much better servo in the process, and you are demanding more out of your equipment running things like flaps.


Just my advice worth what you paid for it.

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Old 10-11-2003, 07:52 AM
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Default RE: Coreless Servos

run your standard servos on 5 cells and you will get your 57oz of torque.


ORIGINAL: ComCity
Well, I ask because someone said I should get 57 oz torque servos for the flaps on my plane and I can't really find them. After the 44 oz standard servos, you have to go to coreless to get the next best price and they are like 3 times as much. I just need more torque....
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Old 10-11-2003, 08:00 AM
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Default RE: Coreless Servos

"If I am not mistaken:
Normal servos have several coil windings (poles) on the armature and permanent magnets along the outer case. This excessive wire is heavy. Coreless motors have magnets in the center and the coil wires are along the case. Coreless are lighter but cost more for the same power output. Also like stated above, since you don't have to convey power to the armature, brushes are not needed."

If you have found a way to eliminate the brushes in a DC motor you have made the greatest discovery since the Wright Brothers. A brushless motor is an AC motor with a DC to AC converter.
A coreless motor is a more efficient but less reliable DC motor that costs about 3 times a standard motor.
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Old 10-11-2003, 08:20 AM
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Default RE: Coreless Servos

If I am wrong, I stand corrected! (but I don't think that I am)
These are the brushless motors I am familiar with which are DC and have magnets on the armature. http://www.micromo.com/Products/cate...iveTab=English

So I guess someone beat me to it

ORIGINAL: dirtybird

"If I am not mistaken:
Normal servos have several coil windings (poles) on the armature and permanent magnets along the outer case. This excessive wire is heavy. Coreless motors have magnets in the center and the coil wires are along the case. Coreless are lighter but cost more for the same power output. Also like stated above, since you don't have to convey power to the armature, brushes are not needed."

If you have found a way to eliminate the brushes in a DC motor you have made the greatest discovery since the Wright Brothers. A brushless motor is an AC motor with a DC to AC converter.
A coreless motor is a more efficient but less reliable DC motor that costs about 3 times a standard motor.
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Old 10-11-2003, 06:02 PM
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Default RE: Coreless Servos

That is an AC motor with a built in DC to AC converter.

There are several ways to get a brushless motor to run if you convert the DC to AC. The easiest way is to convert it to 3 phase AC and use a squrrel cage rotor. You then have a synchronous 3 phase motor that you can control the speed by changing the frequency of the converter. Its a very efficient motor if you don't lose too much in the conversion process.

In a permanent magnet motor the magnet fixed. There is no way to get the magnetic flux developed by the direct current to reverse without swiching the current direction. You have to get the magnetic flux to reverse or the motor will only rotate 180 degrees and stop

I repeat:
If you have found a way to eliminate the brushes in a DC motor you have made the greatest discovery since the Wright Brothers.
Run out quickly and get a patent on it.

Lets get back to the original question.
A coreless motor is an inside out motor. The magnet is placed inside the armeture and is fixed to the motor end piece. The armeture is wound in a cup shape and fitted over the magnet and supported by a bearing in the opposite motor end piece so it is held close to the magnet without touching it. The armeture is wound from copper wire held together with epoxi and contains no metal other than the copper winding. The outside of the motor is a metal cylinder fitted over the armeture and the magnet in such a way that the armeture is in air space betweem the magnet and the outside cylinder.
The motor is more efficient because the armeture has less inertia as there is less rotating metal. It is less reliable because the armeture can only be supported at one end. The armeture still carries current that must be switched.
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Old 10-12-2003, 05:47 PM
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Default RE: Coreless Servos

dirtybird is correct.
There are Brushed and Brushless motors.
The Brushed motors are feed with DC power and controlled by means of Pulse Width Modulation (PWM).
These motors consist mainly of a cylindrical metal case containing a stator and a rotor.
The stator consists usually of two permanent magnets (north and south pole) mounted close to the metal case.
The rotor is mounted on the motor shaft, which rotates inside the stator.
The rotor has several coils (poles) that may either have an iron core or are Coreless.
The Coreless motor has the rotor coils not wrapped around an iron core but just fastened into shape with glue, which makes the rotor much lighter and faster to accelerate and thus suitable for servos.
Since the Coreless don't have iron core they have much less iron losses, which make them more efficient than cored motors.
However, the Coreless motors will not stand continuous high r.p.m. and/or loads without falling apart.
That's why they are generally rather small, with low speed and low power.
As flight power motors the Corless are only used with small indoor planes.

The Brushless motors (don't mix up with Coreless) are 3-phase AC synchronous motors.
Three alternated voltages are applied to the stator's coils sequentially (by phase shift) creating a rotating magnetic field which is followed by the rotor.
It's required an electronic speed controller specially designed for the Brushless motors, which converts the battery's DC voltage into three pulsed voltage lines that are 120deg. out of phase.
The brushless motor's r.p.m. is dependent on the 3-phase's frequency and on the number of poles:
r.p.m. = 2 * frequency * 60/no. of poles.
Increasing the number of poles decreases the r.p.m. but increases the torque.
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Old 10-13-2003, 11:05 AM
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Default RE: Coreless Servos

Dirty Bird and Adam_one are correct. Coreless do use brushes and brushless motors require that the dc power be converted to multiphased pulsed voltage.
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Old 10-13-2003, 06:50 PM
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Default RE: Coreless Servos

i've been dreaming of brushless potless servos for years now. wonder how much they would cost if someone actually produced them?

dave
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Old 10-13-2003, 07:15 PM
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Default RE: Coreless Servos

Hitec HS77BB

Overthrow--Go with the Hitec HS77BB. Give you 61 oz of torque at 4.8 volts, are low profile, and plenty strong. Have used them for years with no problems.

OK all you Hitec haters, I've got my fireproof longjohns on...
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Old 10-14-2003, 07:52 AM
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Default RE: Coreless Servos

You certainly dont need a corless motor servo for flaps. I would recommend the Hitec 625 or 645. The HS 77's would work but just to let you know over the last few years I have burnt up the motors in 4 hs 77's, yes I use them hard but the smaller motor doesnt hold up as well.
Personally for flaps I would just get some cheapy hitec 605's, there strong and cheap. Some have centering issues after continued use but It wont be an issue on flaps. I actually use Hitec 225 minis on the flaps of my GSP corsair (1 on each) They are strong for minis and dont get used much so they should hold up a while
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Old 10-19-2003, 07:48 PM
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Default RE: Coreless Servos

I've been a recent convert to Hitec Digital Servos due to the great centering, holding torque, and programmable features that (with the programmer) greatly simplifies the setup of the plane as well as simplifying the radio programming. For the guys who fly 3D where you have fast wide swings with the servos the coreless may be necessary. For my pattern flying, I've decided to stick with the standard cored Hitec digital servos.
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Old 11-05-2003, 01:08 PM
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Default RE: Coreless Servos

Go to [link]http://www.servohut.com[/link] an get some numbers on servos that meet that torque your looking for with a reasonalbe price tag.
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Old 11-05-2003, 03:09 PM
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Default RE: Coreless Servos

What makes one servo center more accurately than another ? the coreless motor versus 3pole or 5 pole? How does the " digital" come into play?
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Old 11-05-2003, 04:03 PM
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Default RE: Coreless Servos

I have been doing some testing of servos. I cannot find a lot of difference between the centering accuracy of coreless and non coreless motors. That is under a loaded condition. In the no load condition the coreless servo appears to be better.
The digital servo is a lot better than the non digital servo. An explaination of why is on the Futaba WEB site under digital servos. Again I can't find a lot of difference between the coreless or non coreless digital servo.
For why the 5 pole motor is better than the 3 pole motor go to the library and check out a book on DC motors. You won't find an explaination of coreless motors in the book because outside of our field they are rarely used.
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