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  1. #1

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    Brushless Servos

    Could a small brushless motor be used in a large DC servo application? What would be involved in integrating a brushless motor and controller into the existing circuity of a conventional giant scale servo? Can you purchase controllers to operate in both directions FULLY proportionally? (not just partial reverse like some existing controllers) A servo application would require maximum resolution and range in both directions, not *** number forward and ** backward.
    I don't like the fact that so many giant scale planes are operating with 3, 4 or 5 servos on a single surface just to produce the necessary torque. There are much stronger servos out there, (seiko sp?) etc, but I have heard (no experience) that they lack the precision and centering capabilities of the high end hobby servos.
    In a giant scale application (40%50%+) where size is not necessarily an extreme burden, could a large servo be made with a brushless motor? If an outrunner type motor was used, which in and of it's self produces phenomenal torque already, it would not need to be geared down to the extent that the small servo motors are. With a lower gear ratio it would also be very quick. If it was geared more, there could be the incredible torque required of the controls on a large aerobatic aircraft with the oversized surfaces that are so common. If such a motor was connected to an existing circuit board of a high end hobby servo, could you operate that brushless motor and controller through the potentiometer on the outputshaft? What about all of this AND the digital processor of a hobby servo? Is it possible?!?
    This servo would certainly be larger than most, but with brushless equipment getting smaller and smaller almost by the month, it may be more practical. A servo with these components would definitely be expensive, but look at what people are using now. It is not uncommon to see say 3 JR 8611 on a large rudder. Ok now that is almost $350 on that ONE surface. 3 more on each aileron,...two on the elevator halves........... see where this is going? I have done a few searches, and there are lots of industrial AC brushless servo motors, but I have not found a hobby DC unit. I may have just missed it. I really haven't looked thoroughly.
    Anyway,....I was just thinking about this the other day during school. Anyone have any input,..practical?..possible?
    Thanks

  2. #2

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    RE: Brushless Servos


  3. #3

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    RE: Brushless Servos

    Hi guys,
    coreless servos contain brushless motors or not? Somebody could explain the difference (if not)?

    Thanks!

  4. #4

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    RE: Brushless Servos

    I have never seen a coreless servo disassembled. Are they true brushless motors? I thought they were just regular motors turned inside out. Does a coreless motor have brushes? Does it have the brushless controller like a regular brushless motor? Maybe I'm just confused.
    If they are then, couldn't you use a larger brushless outrunner type motor in a giant scale servo?

  5. #5

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    RE: Brushless Servos

    A coreless motor is not a brushless motor It has brushes just like any other PM DC motor.
    A brushless motor is a three phase AC motor. The three phase AC is generated in the controller.
    The three phase motor produces best efficiency at its operating speed. This makes it a good choice for driving a propeller. It is not easily controlled as to speed and direction. It is not a good choice for a servo. The advances in electronics may overcome these limitations but it would take determined developement program.
    The coreless motor developes its maximum torque a 0 RPM and is easily controlled as to speed and direction. This makes it the best choice for servos. Overheating of the armeture in the larger sizes is a problem so it is not a good choice for driving a propeller with the high current requirements. Otherwise it might be just as efficient as the brushless motor but the brushes would have to be well shielded.
    dirty old men need love too.

  6. #6

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    RE: Brushless Servos

    Ok, a few years ago I was thinking about the question of brushless servos and finally got around to posting it a little over a year ago. Futaba now offers brushless digital servos. Anyone know how this was accomplished, considering the aforementioned problems with brushless motor torque at 0RPM?

    Thanks

  7. #7
    Silent-AV8R's Avatar
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    RE: Brushless Servos

    Futaba will soon have three new brush less servos out. Here is what they have released about them:

    BLS451 has a torque of 139 oz-in and speed of .11 @ 6V
    BLS351 has a torque of 194 oz-in with a speed of .13 @ 6V
    BLS251 has a torque of 51 oz-in and speed of .06 @ 4.8V

    1. The brushless servos offer greatly improved response time over
    other servos. Specifically, the response time on the brushless
    servos has been decreased from 10ms to 7ms. This means that the
    servos will react much, much faster to any control input.

    2. Significantly increased life span. The new brushless servo
    motors will last more than five times longer than servos that include
    brushed motors.

    3. Lower operating temperatures. As there are not any brushes on
    the motor armature, there is no spark produced when the servo motor
    is in operation. Thus, the temperature remains very constant within
    the servo rather than increasing as they do in a brushed motor
    servo.

    Furthermore, thanks to the motor design, the outer coils act as a
    heat sink dissipating any heat that does occur. As an added benefit,
    Futaba is able to increase the torque or speed of the servos without
    increasing the case dimensions.

    4. Vibration & Shock. Unlike servos that used brushed motors, the
    brushless servos from Futaba are less susceptible to the effects of
    vibration and/or shock. While we don't want the modeler to abandon
    the use of the servo grommets and rubber mounts, these servos are
    simply less apt to experience difficulties from poor or improper
    installation.

    Additionally, the inertia of the standard motors also facilitates the
    effects of vibration on the servo's performance. By eliminating this
    inertia in a brushless servo, Futaba has reduced this possibility.

    5. Power consumption. Brushless servos consume approximately the
    same amount of power as their digital servo counterparts.

    6. Centering. Centering is the same as it is with the digital
    servos. The dead band is also equal to the digitals.

    7. Case size. Brushless servos are the same as a standard-size
    servo.

    8. Increased resolution (specifics to be confirmed later) for
    smoother operation.

    9. Samarium Cobalt magnet for better performance and increased
    holding power.

    10. Dual ball bearings.
    Team Futaba - RClipos.com

  8. #8
    Hibrass's Avatar
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    RE: Brushless Servos

    Damn those servo specs look nice....

    The next big question.... Price of those bad boys....?

    Hibrass
    Ed \"Hibrass\" Harley Club Saito #457
    \"If you don\'t know the Dog, don\'t yank his chain.\"

  9. #9
    Silent-AV8R's Avatar
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    RE: Brushless Servos

    Nothing has been said about price or dates that they will be available.
    Team Futaba - RClipos.com

  10. #10
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    RE: Brushless Servos

    Hi Dirtybird,
    Bear with me, I have to get my 2 cents in on what makes a motor "brushless"
    Actually AC motors, either single or polyphase, are not "brushless" motors at all, the industry term "brushless" refers to motors that are electronically "commutated" and function with the characteristics of a brushed motor (KV??? timing?????), the industry designation for these motors is "brushless DC motors"
    The motors we use, while they may look a lot like a 3 phase ac motor, are an anomaly as motors go, they cannot be used without some form of controller, either a variable frequency drive or a brushless controller, they are basically unusable on fixed frequency ac (50/60Hz) as they lack the ability to self start under those conditions.
    Our brushless controllers are not a dv/ac inverter, as they do not create ac independant of the motor, they provide commutation to the motor, which is a closed loop system, using feedback from the motor to time the switching/commutation (yes, dc brushed motors internally are ac motors, but we call them dc, since that's what we feed them)
    Motors used with a BLDC contoller have their RPM determined by the voltage applied (in our case PWM), just as their brushed counterparts, hence the use of a KV rating.
    AC motors (non-commutated) have their RPM determined by the line frequency, rather than voltage. That's why oour Dremel tools must use a series wound brushed motor to gives us 30KRPM an ac induction motor on 60Hz has a max no-load RPM of about 3550 (assuming 2 pole) no way will it spin faster without increasing the frequency.

    Holiday cheers,
    Pete
    \"If the woman don\'\'\'\'\'\'\'\'t find you handsome, they should at least find you handy\"

    [Red Green]

  11. #11

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    RE: Brushless Servos


    ORIGINAL: pilotpete2

    Hi Dirtybird,
    Bear with me, I have to get my 2 cents in on what makes a motor "brushless"
    Actually AC motors, either single or polyphase, are not "brushless" motors at all, the industry term "brushless" refers to motors that are electronically "commutated" and function with the characteristics of a brushed motor (KV??? timing?????), the industry designation for these motors is "brushless DC motors"
    The motors we use, while they may look a lot like a 3 phase ac motor, are an anomaly as motors go, they cannot be used without some form of controller, either a variable frequency drive or a brushless controller, they are basically unusable on fixed frequency ac (50/60Hz) as they lack the ability to self start under those conditions.
    Our brushless controllers are not a dv/ac inverter, as they do not create ac independant of the motor, they provide commutation to the motor, which is a closed loop system, using feedback from the motor to time the switching/commutation (yes, dc brushed motors internally are ac motors, but we call them dc, since that's what we feed them)
    Motors used with a BLDC contoller have their RPM determined by the voltage applied (in our case PWM), just as their brushed counterparts, hence the use of a KV rating.
    AC motors (non-commutated) have their RPM determined by the line frequency, rather than voltage. That's why oour Dremel tools must use a series wound brushed motor to gives us 30KRPM an ac induction motor on 60Hz has a max no-load RPM of about 3550 (assuming 2 pole) no way will it spin faster without increasing the frequency.

    Holiday cheers,
    Pete
    Polyphase AC motors have no brushes. Therefore they are true brushless motors. The driving force is provided by the rotating magnetic field provided by the polyphase AC. The armeture is a shorted wire loop. The generaric name is a squirrel cage motor. They start of thier on accord when provided three phase AC. Your statement that they are not usable is only true when used on single phase. Even then they work if something starts them. Your washer machine motor is probably a squirrel cage motor with a capacitor that is switched out after the motor starts. The capacitor creates two phases that starts the motor.
    You can make a brushless motor by creating the required multiphase AC and using the squirrel cage motor but it is not easily controlled.
    I don't know what the new Futaba servos are. I would like to get ahold of one and test it.
    dirty old men need love too.

  12. #12
    pilotpete2's Avatar
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    RE: Brushless Servos

    Hi Dirtybird,e
    This will be an interesting development to watch as to the brushless servos.
    But back to motors.
    "Polyphase AC motors have no brushes. Therefore they are true brushless motors."
    No, brushless motors were not developed till the 1970's roughly, induction motors single and polyphase have been around for over a century, (if you called an AC induction motor "brushless" in front of an electrician years ago, he would kinda look at you strange and say something to the effect that " well no, they don't have brushes, they're induction motors" or maybe "Brooshes! I don't need no steenking brooshes!!) the fact that they have no brushes does not make them "brushless" as that term is incomplete and is not used outside of the R/C world, in the industries that use them and developed them they are always designated as "brushless DC motors" The term "brushless" on it's own is confusing as it created the impression that any motor that has no brushes is "brushless" but the term should be reserved for motors that are commutated motors without mechanical brushes, so in effect they are "brushless motors", that still run in commutated mode, and since the voltage scorce is DC before commutation, the term "brushless DC motor" makes a bit more sense.
    As to the nature of the BLDC motors we use, while the 3 phase winding is consistant with a normal ac motor design, the fact we have a rotor made up of permanent magnets is not consistant with ac motor design, it would have to run in synch with the magnetic field and would have no ability to self start, functional synchronous ac motors use an asynchronous element to spin it up near to synch speed, when it goes into synch the asynch part no longer has current flow, one exception to this are the "funky" synchronous reluctance motors used in cheap ac analog clocks (remember those) they of course will start bassakwards 50% of the time, so they have a clever mechanism to stall the rotor, then kick it back in the correct direction, a real "Rube Goldberg" design.
    Here are a couple of links with some good info.
    http://www.electricmotors.machinedes...m/BDEList.aspx
    http://en.wikipedia.org/wiki/Brushle...electric_motor
    I believe the reason the confusion of the way the brushless motor works arrises when folks look at the currents between the motor and the controller, they see AC, well thats exactly what you would see in the same place in a Mabuchi can motor, with a brushless motor if you look at the current at motor terminals, you are literaly "inside" the motor as you are looking at the product of commutation, the controller runs in a closed loop with the physical motor, in this arrangement they can only be viewed as one, and not as a separate motor and voltage supply, neither functions without the other.
    Well I have been more than a bit guilty of taking this thread off topic, so I should appologize.
    The idea of brushless servos deffinitly has "cool" factor, recently when the idea of brushless motors in cordless tools was brought up, my attitude was like "well maybe down the road, but not anytime soon", yeah right, seems they are already on the market, maybe the market will be driven this way as the cost of the electronic controlls keeps going down, while the cost of the mechanical brushes/commutator mechanisms keep going up.
    Best wishe fo the Holidays
    Pete
    \"If the woman don\'\'\'\'\'\'\'\'t find you handsome, they should at least find you handy\"

    [Red Green]

  13. #13

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    RE: Brushless Servos

    So you are saying an induction motor is not a brushless motor just because the term brushless was not coined until years after the induction motor was invented even though they have no brushes?
    OK I give up
    dirty old men need love too.

  14. #14
    pilotpete2's Avatar
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    RE: Brushless Servos

    Hi Dirtybird,
    We'll just have to agree to disagree on this one But I'll stick by my guns that "brushless" refers to brushless commutated motors, or more specifically brushless dc motors. The fact that ac induction motors have no brushes is stating the obvious, but these motors also have nothing in common with the brushless motors we use in the hobby, our computers etc.
    Have a great Holiday,
    Pete
    \"If the woman don\'\'\'\'\'\'\'\'t find you handsome, they should at least find you handy\"

    [Red Green]

  15. #15

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    RE: Brushless Servos

    Thanks. This is exactly the type of discussion I was looking for a year ago. Any hypotheses on what specifically futaba is releasing as a brushless motor in the new servos? Speculation on current consumption, practicality, etc?

  16. #16

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    RE: Brushless Servos

    OK here is a good question, will they run on an unregulated 7.2 Li-poly??? if not, they should. The DX-7 reciever will, now we just need servos that will

    John
    If we all think the same, only one of us is necessary

  17. #17

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    RE: Brushless Servos

    The discussion about "brushless and/or coreless" is interesting, and I appreciate the knowledge you guys have....I just have this question:
    Are the Futaba "Brushless Servos" good servos and are they a good value?
    The specs on the BLS451 look very good and I'm thinking of getting some of these to use with my 12FG.
    I plan to use the A123 6.4 volt battery with these servos.
    For those of you who already have these servos...how do you like them?
    How are these servos performing in the "real world"
    Are you glad you bought them and do you recommend them?
    I would appreciate any advice or information.

    Regards
    JC
    Regards
    JC

  18. #18

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    RE: Brushless Servos

    Is anybody in here?
    Regards
    JC

  19. #19
    Flying Geezer's Avatar
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    RE: Brushless Servos

    I saw the bl451 on the Tower site, I think. $89.00.
    Flying Geezer

  20. #20

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    RE: Brushless Servos

    Hi Geezer,
    Good to hear from you. That young man in the big hat sure reminds me of my oldest son at that age.
    About the servos: I'm just wondering if anyone in here is using these "Brushless" servos and if so,
    how are they working out?
    Regards JC
    Regards
    JC

  21. #21

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    RE: Brushless Servos

    I just ordered three of them from Tower, they will arrive next week. I'll put them in my Compass Model Knight Sport to control the CCPM. I'll post what happens

  22. #22

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    RE: Brushless Servos

    Wow, this is the thread that won't die. Original post in 2005, revived in 2006, 2007, missed 2008 and now 2009.

    As a note, I have the BLS451's in my Trex600N Pro and they work great.


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